how brain works

8/8/2019 How Brain Works

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How does the brain work?Question: How does the brain work?N Scherer

Answer:Mechanically or conceptually? A subway system works mechanically by

cars on steel wheels, rails, and 500 volts of electricity shunted hitherand yon on overhead wires. Conceptually though it's a widget to get folksfrom where they live to where they work, and it works by figuring out thepaths they take, assigning trains to those routes, and discounting faresoff-peak to even out the rush-hour crowds.

Mechanically the brain is billions of cells called neurons that canproduce little bursts of electricity that can be passed from cell to cell.(Brain neurons are densely interconnected.) These bursts produce weakelectric fields at the surface of the head that can be recorded, hence theEEG ("electro-encephalogram", Greek for recording (gram) of head (cephalus)electricity, aha.) Coarse features in the EEG are found to be related tobroad categories of brain activity: larger, slowly-varying electric fields

indicate sleep, smaller, faster-varying fields alertness, etc. More subtlemeasurements map increased electrical activity in certain *regions* of thebrain when people remember, speak, or blow their nose, and directelectrical stimulation of certain areas of exposed brains producessensations, movement, memories of the Kennedy Administration, etc. Thusthe wide assumption is that it is the pattern of the electrical bursts ofthe neurons that constitute thought, along with perhaps chemical changes ineach neuron to account for memory, learning, personality and otherslowly-changing brain behavior. An article in the April 1994 issue of"Scientific American" details some recent nifty experiments on mappingbrain activity and correlating action and thought. Also consider the booksof Oliver Sacks on brain dysfunction.

You'd think knowing how the brain works mechanically would tell youipso facto how it works conceptually. Alas no. Conceptual understanding ofbrain function is much more incomplete. Doubtlessly the most influentialthought on thought (argh), and a major force shaping social currents in the20th century, is the hypothesis of the division into conscious andunconscious mind. Much is known about learning and problem-solvingtechniques of the conscious mind, and its organization of basic thinkingtasks (e.g. remembering, planning, perception), but we don't know themechanics of, and cannot duplicate ourselves, the two most outstandingfeatures of the mind: its ability to respond originally, i.e. create, andits self-awareness, i.e. consciousness. For amusing essays on the latterconsider "The Mind's I" by Daniel Dennett and Douglas Hofstadter, or theshort stories of Stanislaw Lem. One of the most popularly influentialrecent books is Julian Jaynes' "The Origin of Consciousness in theBreakdown of the Bicameral Mind," which has left us with left- and right-

brainedness on the brain. My favorite paradigm is that *intelligence*consists of having a mental model of the world in which to try out newideas for future action off-line (which as Karl Popper says enables"our hypotheses to die in our stead"), while *consciousness* consists ofincluding in that mental model a little model of *ourselves* as well. Tobe conscious is then to be able to watch yourself watch the world. Yow.Christopher Grayce


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How Brain Cells Work. Part II The Action Potential

Silvia Helena Cardoso, PhD, Luciana Christante de Mello, MSc and Renato M.E.Sabbatini,PhD

Animation and Art: Andr Malavazzi

E lectricity is a natural phenomenon in our body and it is involved in the specific functions of certain special cells in the brain and in smooth and striated muscles. Each pattern of light, sound,heat, pain, each twinkle, finger snap, each thought translates into a sequence of electric pulses.How does it happen?

N erve cells possess properties similar to other cells in many aspects: they feed, breed, undergoprocesses of diffusion and osmosis in their membranes andso on, but they differ in a major aspect: they process information. The ability of nerve cells to process information relies upon thespecial properties of the neuron membrane, which controls the flow of substances to the inner cell (sodium, calcium and potassium ions and so on).

N eurons do not exist in isolation: they also connect themselves to each other,forming the so-called neural chains, which transmit information to other neurons or muscles. The nerve impulsespropagates throughout these chains.Two kinds of phenomena are involved in the nervousimpulse: electric and chemical. The electrical events propagate a signal inside a neuron, and thechemical events transmit the signal from one neuron to another or to a muscle cell. The cellcontact or junction between one neuron and the next, or between a neuron and a muscle cell iscalled synapse ,which will be dealt with in future articles.

The nervous impulse

A nervous impulse is the transmission of an electric change along the membrane of a neuronbeginning at the point of stimulus. The normal direction of the impulse in organism is from the

body cell to the axon (see the article on the structure of the neuron on Brain & Mind issue #7).

This nervous impulse or action potential ,is a propagated, sudden and rapid change intransmembrane potential. N ormally,as we have seen in the previous article in this series, theneuron membrane is polarized at rest, with a negative potential ( -70 mV). The action potentialconsists of a rapid reduction of the negativity of the membrane to 0mV and the inversion of thispotential to values up to some +30mV, followed by a very quick return to value somehow more


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negative than the potential at rest of -70mV.

Potencial de ao exibido em um osciloscpio.

The nervous impulse is known as actionpotential. The action potential is aphenomenon of electro-chemical nature andoccurs due to the changes in the permeabilityin the neuron membrane. These changes inpermeability allow the flow of ions from oneside of the membrane to the other. Given thatthe ions are electrically charged particles,changes in the electric field generated bythese charges take place.

One way we could visualize the actionpotential is by means of a thousand-foldelectronic amplification of the electric changescaptured by an electro deplaced in contactwith the neuron and representing theamplitude in volts,as a function of time, thanksto a piece of equipment calledoscilloscope. On the screen on the left, thegreen line represents the evolution of actionpotential in a point in the neuron (from left toright). The initial straight line corresponds tothe voltage of the resting potential of themembrane. The first alteration is an artifactcaused by the beginning of electricstimulation. After a certain lag, the potentialstarts to increase (depolarization phase) andthen to decrease (repolarization phase). After ashort excess repolarization, the membranepotential returns to the value prior tostimulation. All these phenomena added upoccur injust over two miliseconds.

To imagine how thenervous impulse

happens, observe thefigure on the left.Theperception of acute painwhen a sharp objectpenetrates your foot iscaused by the generationof certain action potentialin some nervous fiber


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in the skin. It is believedthat the membranes of these cells have sodiumchannels that open whennerve terminals of the cellare stretched.The initialchain of events is:

1.Sharp object penetratesthe skin; 2 .The membranes of nerve fibers in the skinare stretched; 3.Channels permeable tosodium ( N a +)are opened.

Due to the concentrationgradient and negative

charge in extracellular fluid,ions enter the fiber by means of thesechannels. Sodiumentrance(yellow balls)depolarizes themembrane, that is, theside of membrane bathedby extracellular fluidbecomes less negative inrelation to the cellinterior. If thisdepolarization, called

generator potential ,reaches a critical point,the membrane thengenerates an actionpotential. The criticalpoint of depolarizationthat must be overcome inorder to fire an actionpotential is calledthreshold .The actionpotentials are caused bydepolarization of themembrane above thethreshold.

In the repolarizationphase, the sodiumchannel is deactivatedand the conductivity of membrane for potassiumincreases. These positiveions follow its chemical and


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electrical gradient andexit from the cell, thusgradually inverting themembrane potential(green balls)

In the recovery phase, theactive sodium/potassionpump (blue channel in thefigure) restablishes theionic levels which werealtered during the actionpotential: for each sodimion which is transportedfrom the inside to theoutside, a correspondingpotassium is transportedin the opposite direction.

F ig.1.Simple Reflex -Human feet in contactwith a tack (externalstimulus). M edula espinhal =spinal cord; Para oCrebro= to the brain

(Click on the button "Re-start"to see the animation).

The skin perforation is transduced into signals that travel upwards viasensorial nerves (direction of information flow shown by arrows). Thisinformation arrives at the spinal chord and is distributed to interneurons(neurons that provide intermediate connections with other neuron chains).Some of these neurons send axons to the sensorial region of the brainwhere the sensation of pain is registered. Other make synapses with motor neurons,which send signals downward to the muscles. The motor

junctions command the muscle contraction and withdrawal of the foot.

This is an example of a neuron chain called reflex arc.

How the Action Potential Works

Local or Generator Potential

As we have seen in the previous article of this series, the membrane of non-stimulated neuron(at rest)presents a difference of electrical potential between the interior and exterior of the cell of approximately 70 mV; a potential, which is maintained while the cell, is alive. This constitutes thepotential of membrane potential at rest. How is it possible that the potential at rest can be

disturbed up to generating an action potential? When a stimulus is applied to the membrane, a temporary unbalance takes places between theelectric charges of the membrane and the ions concentration in each side of the membrane, whatis called a local potential . Whenever the membrane, starting at a potential at rest, is depolarized toaround -50 mV, action potentials are generated. The potential that launches the action potential iscalled threshold (see figure above). At this threshold potential, the membrane is unstable. Itspontaneously diminishes its polarity, very quickly and generally reaches an inversion of polarity:then follows a rapid increase(ascending curve) of the action potential that goes beyond potentialzero and goes to an "overshoot". This state of diminishing charge, initiated at threshold levels, is


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spontaneous and progressive. It is also called an "excitation" The excitation has a short duration,normally less than one 1 ms (milisecond), being comparable to an explosion that rapidlydissipates itself.

A stimulus that tends to diminish the natural polarity of the membrane is called depolarizingstimulus. One stimulus that tends to increase the natural polarity is called polarizing stimulus.

The local potential does not propagate, that is, it remains limited to the neighboring membrane atthe local of the stimulus.

Properties of Generator Potentials

The local potential is very important to the functioning of the neuron. As we have seen in thechapter on neuronmorphology , the nerve cell has many short extension of cell bodycalled dendrites .A neuron can receive simultaneously many depolarizing and hyperpolarizingstimuli coming from other neurons or from external sources of stimulation, in several parts of thedendrites and the cell body. Each stimulus generally provokes a small change in the localpotential. When two local potential are very close (physically) they can "overlap" that is, there is asum of their amplitudes). Or they can cancel each other, when they are in opposite directions.This is called a " spatial sum ".It can happen also that two successive stimuli, separated from eachother by a very short interval of time, occur at the same point in the membrane.Then, before thelocal potential caused by the first stimulus returns to normal, the second stimulus intervenes,either by summing or subtracting to the previous one. This is called a " temporal sum ".

What the neuron does is a "summing up" of all local potentials. If the result is towards a major depolarization, from a certain threshold on,then a very important event takes place, which is theaction potential.Let see why and how it occurs.

Initial Steps

When a stimulus reaches the membrane of the neuron, there is a small local depolarization.Thisstimulus can be of a photic, chemical, physical or pharmacological nature, depending on the

sensibility of the cell. The depolarization provokes the opening of N a+ and K+ channels that arevoltage dependent and allow the flow of ionic current from one side to the other side of thecell.Simultaneously there a flow of N a+ from the outside to the inside (as we have seen in theprevious chapter, there is a higher concentration of sodium outside), which tends to further depolarize the membrane; and a flow ofK+ from the inside to the outside that tends to repolarizethe membrane.

"All or N one"

There is, however, an important difference between N a+ and K+ channels: N a+ channels openmuch more rapidly than the K+ channels. Therefore, the depolarization causes a feedback effect:the more sodium enters the channel, the more is become permeable. It is like an avalanche of depolarization that eventually leads to a point when N a+ depolarizing current is much higher thanK+ repolarizing current; this point is called THRESHOLD POTE N TIAL.From the moment it isreached, the process can not be reverted again and there is an abrupt inversion of membranepolarity, that is , the action potential. In the majority of neurons, the value of threshold potential isaround -30mV.

Once the threshold is attained, the action potential occurs with a fixed amplitude and duration. If the threshold is not attained, that is, if the depolarization of the sodium intake was not strongenough, there is no action potential.That is why the scientist called this an " allor none "phenomenon, much alike a digital mechanism (0 or 1)


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Back to N ormal

The depolarization phase of action potential is abrupt and very rapid: in takes place in less thanone milisecond. Soon after reaching the maximum peak of depolarization ( which inverts themembrane potential to some +10 to+ 2 0 mV), it begins to return to normal, that is, towards itsvalue at rest. This phenomenon is called repolarization ,and something very important takes place:

while this recovery is going on, the neuron remains insensitive to new stimuli (the refractoryperiod ).

Why does it happen? To understand it, we have to know another importance differencebetween N a+ e K+ channels: the first undergoes inactivation but not the latter.

After the action potential occurs, the N a+ channels change to an inactive state during which theyare unable to respond to a new stimulus, that is, they remain close to new intakes of sodium.Meanwhile, the K+ channels, that are still opening themselves, due to its characteristic slowness,remain open and allow an import out flow of K+ ions. This leads to the repolarization of themembrane, that we mentioned above. It can "undershoot" in its final phase, provokind a small andtransient hyperpolarization .

Sodium channels can only be stimulated again after the membranes are completely repolarized. If there is no sufficient number of N a+ channels in this situation,it is possible to stimulate theneuron, but it will respond only if the intensity is much higher. This constitutes the so-called relative refractory period . When the channels are completely closed and it is impossible tostimulate the neuron, no matter how intense may be the stimulus, we call it the absolute refractoryperiod.

See also: " How N erve Cells Work. Part I

See in the next Installment of the series: The propagation of action potential throughout the nerveFiber (mielinic and amielinic fiber, continuous and saltatory conduction. Composite actionpotential (fibers). The speed of action potential and how it can be measured.Clinical relevance.

The Authors


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Silvia HelenaCardoso ,PhD.Psychobiologist, master and doctor inSciences, Founder andeditor-in-chief,Brain andMind Magazine, StateUniversity of Campinas.

Luciana Christante deMello , MSc. inNeuroscience,Doctoral student,Faculty of MedicalSciences, State

University of Campinas. AssociateResearcher, Centerfor BiomedicalInformatics,

Renato M.E.Sabbatini ,PhD.Doctorin Sciences(Neurophysiology) bythe State University of So Paulo Associate

Director of the Centerfor BiomedicalInformatics of theState University of Campinas, Brazil, andpresident of theEditorial Board,Brain &Mind Magazine.

Andr Malavazzi Designer,Instute of Arts and Centerfor BiomedicalInformatics, StateUniversity of Campinas.

Copyright (c) 2000 State University of Campinas , BrazilAn initiative: Center for Biomedical Informatics

Published: 15.Jan.2000


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Caution: The image inside the brain are neurons, but they are not placed in this manner. Click here to see how the brain looks like in this view.

N eurons: Our Internal Galaxy

Silvia Helena Cardoso, PhD

Not only the stars in the Universefascinate Man with its impressivenumbers. In another universe, our

own, biological one, a gigantic "galaxy" with billions of small

neural cells forms our brain and the rest of the nervous system, and

communicate among themselvesby means of flashes of

electrochemical pulses. They areresposible for everything: our

feelings, thinking, emotions, pain,dreams, movements and sensations, and many other mental

and physical functions. Without them, it would be impossible to

achieve our rich internal world and to communicate with the

surrounding environment, by means of sound, smell, taste,

touch and light; including that of the stars in our Universe.

.

Contents:

Structure of the N euron Parts of the N erve Cell and Their Functions

The Brain is Grey and White.Why?


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What Make N eurons Different From Other Cells?

Anatomical Diversity of N eurons Gallery of N eurons

All stimuli of our environment causing sensations such as pain and hot, allfeelings, thoughts, programming of motor and emotional responses, neural basesof learning and memory, actions of psychoactive drugs, causes of mentaldisorders, and any other action or sensation of the human being cannot beunderstanding without the knowledge of the fascinating process of communication between neurons.

N eurons are specialized cells. They are made to receive certains specificconnections, to perform appropriate functions and pass their decision of aparticular event to other neurons which are also concerned with those events.These specializations include a cell membrane, which is specialized to conveynerve signals as electrochemical pulses; the dendrite, (from the Greek dendron,or tree) which gets and delivers the signals, the axon (from the Greek axoon , or axis), the conducting cable of electrical signals, and points of synaptic contacts, where information can be passed on from one cell to another (see fig.1).

Fig.1. The structure of the neuron. A typical neuron has four morphologically defined regions: dendrites (1), cell body ( 2 ),axon (3), and presynaptic terminals (5).

N eurons receive nervesignals from axons of other neurons. Mostsignals are delivered todendrites (1). Thesignals generated by aneuron are carried awayfrom its cell body ( 2 ),which contains the

nucleus ( 2 a), thestorehouse of geneticinformation. Axons (3)are the main conductingunit of the neuron. Theaxon hillock ( 2 b) is thesite at which the cell's


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signs are initiated.Schwann cells (6),which are not a part of anerve cell, but one of the types of glial cells ,perform the importantfunction of insulatingaxons by wrapping their membranous processesaround the axon in athight spiral, forming amyelin sheath (7), afatty, white substancewhich helps axonstransmit messages

faster thanunmyelinated ones.Themyelin is broken atvarious points by thenodes of Ranvier (4), sothat in cross-section itlooks rather like a stringof sausages. Branchesof the axon of oneneuron (the presynapticneuron) transmitsignals to another neuron (thepostsynaptical cell) at asite called the synapse(5). The branches of asingle axon may formsynapses with as manyas 1000 other neurons.

See also: Parts of the N erve Cell and Their Functions

What Make N eurons Different from Other Cells?

Just like other cells, neurons feed, breath, have the same genes, the samebiochemical mechanisms and the same organelles. So, what makes the neurondifferent ? N eurons differ from other cells in one important respect: they processinformation . They must gather information about the internal state of the


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organism and his external environment, evaluate this information, and coordinateactivities appropriate to the situation and to the person's current needs.

The information is processed through an event known as the nerve impulse .Anerve impulse is the transmission of a coded signal from a given stimulus along

the membrane of the neuron, from the point that it was stimulated.Two types of phenomena are involved in processing the nerve impulse: electrical andchemical . Electrical events propagate a signal within a neuron, and chemicalprocesses transmit the signal from one neuron to another or to a muscle cell. Thechemical process on interaction between neurons occurs at the end of the axon,called synapse . Touching intimately against the dendrite of other cell (but withoutmaterial continuity between both cells), the axon releases chemical substancescalled neurotransmitters , which attach themselves to chemical receptors in themembrane of the following neuron.

The Brain is Grey and White. Why?

Maybe you have heard the term "grey matter" for the brain; there is also "whitematter". In a section made through the brain, it is easy to see both grey and whiteareas. The cortex and other nerve centres are grey, the regions in between, white.The grey coloration is produced by the aggregation of thousands of cell bodies,while the white is the color of myelin. The white color reveals the presence of bundles of axons passing through the brain, rather than areas in whichconnections are being made. N o neuron has direct conection with any other. Atthe far end of the axon are a number of terminal filaments, and these run up close

to other neurons. They may be close to the dendrites of the other neuron(sometimes to special structures called dendritic spines, or close to the cell bodyitself. Where the first neuron comes close to the second neuron, a synapse isformed, a space acreoss which the first neuron communicate with the second.N ext: Anatomical Diversity of N eurons

Resources


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The Brain and the N ervous System Types of N eurons The Biological N euron The N euron Lights, Camera, Action Potential!! How Animals Transmit Informations Gallery of N eurons

References: N euroscience: Exploring the Brain. Bear, M.F.; Connors, Barry W. e Paradiso, Michael (eds.)-Williams & Wilkins, 1996.

Human Mind Expalined - A. A. Greenfield (ed) - Henry Holt And Company, 1996. 1

The Author

Silvia Helena Cardoso , PhD, Psychobiologist, Director and Editor-in-chief, Brain & Mind.

Reviewed by the neuroanatomist Dr. N orberto Cysne Coimbra , MD, PhD.Laboratory of N euroanatomy and N europsychobiology, School of Medicine of Ribeiro Preto, University of So Paulo (USP), Ribeiro Preto, Brazil

fMRI response in medial frontal cortex that depends on the temporal frequency of visual input fMRI


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Realistic shaped Boundary element Model (BEM) of the head Model(BEM)

Topography of ADHD group coherence elevation at 8 Hz in the alert interval ADHD 8 Hz

Neuroscientists , along with researchers from allied disciplines, study how the human brainworks. , ,

. Such research has expandedconsiderably in recent decades.

. The "Decade of the Brain ", an initiative of the United States Government in the1990s, is considered to have marked much of this increase in research. [ 14 ]

, 1990, .[14]

Information about the structure and function of the human brain comes from a variety of

experimental methods. . Most information about th

cellular components of the brain and how they work comes from studies of animal subjects,using techniques described in the brain article.

, . Some techniques,

however, are used mainly in humans, and therefore are described here. ,, , .


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Computed tomography of human brain, from base of the skull to top, taken with intravenous contrastmedium , ,

[ edit ] EEG [ ] EEG

By placing electrodes on the scalp it is possible to record the summed electrical activity of thecortex, in a technique known as electroencephalography (EEG). [ 15 ] EEG measures masschanges in population synaptic activity from the cerebral cortex, but can only detect changesover large areas of the brain, with very little sensitivity for sub-cortical activity.

,

, (EEG).[15]

EEG

, - . EEG recordings can detect events

lasting only a few thousandths of a second. EEG . EEG recordings have goo

temporal resolution, but poor spatial resolution. EEG , .

[ edit ] MEG [ ] MEG

Apart from measuring the electric field around the skull it is possible to measure the magneticfield directly in a technique known as magnetoencephalography (MEG). [ 16 ] This technique hasthe same temporal resolution as EEG but much better spatial resolution, although not as good asMRI. ,

(MEG). [16] , EEG,

, MRI. The greatest disadvantage of MEG isthat, because the magnetic fields generated by neural activity are very weak, the method is only


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capable of picking up signals from near the surface of the cortex, and even then, only neuronslocated in the depths of cortical folds ( sulci ) have dendrites oriented in a way that gives rise todetectable magnetic fields outside the skull. MEG ,

,

, , (sulci) .

[ edit ] Structural and functional imaging [ ]

Main article: Neuroimaging :

A scan of the brain using fMRI fMRI

There are several methods for detecting brain activity changes by three-dimensional imaging of local changes in blood flow.

. The older methods are SPECT and PET , which depend on injection of radioactive

tracers into the bloodstream. SPECT , . The newest metho

functional magnetic resonance imaging (fMRI), has considerably better spatial resolution andinvolves no radioactivity. [ 17 ] Using the most powerful magnets currently available, fMRI canlocalize brain activity changes to regions as small as one cubic millimeter. ,

(fMRI), .[17]

, fMRI . The downside is that the temporal resolution is poor: when brain

activity increases, the blood flow response is delayed by 15 seconds and lasts for at least10 seconds. :

, 1-5 10 . Thus, fMRI is a very useful tool fo

learning which brain regions are involved in a given behavior, but gives little information aboutthe temporal dynamics of their responses. , fMRI

, ,

. A major advantage for fMRI is that, because it is non-invasive, it can readily be used on


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human subjects. fMRI , , .

[ edit ] Effects of brain damage [ ] Main article: Neuropsychology :

A key source of information about the function of brain regions is the effects of damage to them.[ 18 ] In humans, strokes have long provided a "natural laboratory" for studying the effects of braindamage.

.[18] ,

. Most strokes result from a blood clot lodging in the brain and blocking the local bloodsupply, causing damage or destruction of nearby brain tissue: the range of possible blockages isvery wide, leading to a great diversity of stroke symptoms.

,

, . Analysis of strokes is limited by the fact that damage often crossesinto multiple regions of the brain, not along clear-cut borders, making it difficult to draw firmconclusions.

, , .

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Electrocorticography Electrocorticography

From Wikipedia, the free encyclopedia , Jump to: navigation , search : ,

El ectrocorticography (ECoG) is the practice of using electrodes placed directly on the exposedsurface of the brain to record electrical activity from the cerebral cortex . El ectrocorticography (ECOG)


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. ECoG may be performed either in the operating room during surgery(intraoperative ECoG) or outside of surgery (extraoperative ECoG). ECOG

( ECOG) (extraoperative ECOG). Because acraniotomy (a surgical incision into

the skull) is required to implant the electrode grid, ECoG is an invasive procedure.

( ) , ECOG . ECoG is currently considered to be the goldstandard for defining epileptogenic zones in clinical practice. ECOG " " epileptogenic .

C ontents

[hide ]

y 1 History 1 y 2 Electrophysiological basis 2 y 3 Procedure 3 y 4 DCES 4 DCES y 5 Clinical applications 5

o 5.1 Intractable epilepsy 5,1 y 6 Research applications 6 y 7 Recent advances in ECoG technology 7 ECOG y 8 References 8 y 9 See also 9 . y 10 External links 10

[ edit ] History [ ]

ECoG was pioneered in the early 1950's by Wilder Penfield and Herbert Jasper , neurosurgeonsat the Montreal Neurological Institute . [ 1 ] The two developed ECoG as part of their groundbreaking Montreal procedure , a surgical protocol used to treat patients with severeepilepsy . ECOG 1950 Wilder Penfield

Herbert Jasper , . [1] ECOG ,

. The cortical potentials recorded by ECoG were used to identify epileptogenic zones regions of the cortex

that generate epileptic seizures . ECOG epileptogenic - . These zones would then be surgically removed from the cortex

during resectioning, thus destroying the brain tissue where epileptic seizures had originated.

resectioning, . Penfield and Jasper also used electrical stimulation during ECoG recordings in

patients undergoing epilepsy surgery under local anesthesia . [ 2 ] This procedure was used to


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explore the functional anatomy of the brain, mapping speech areas and identifying thesomatosensory and somatomotor cortex areas to be excluded from surgical removal. Penfield Jasper ECOG

. [2]

, somatomotor .

[ edit ] El ectrophysio logica l basis [ ]

ECoG signals are composed of synchronized postsynaptic potentials (local field potentials),recorded directly from the exposed surface of the cortex. ECOG

( ), . The potentials occur primarily in cortical

pyramidal cells , and thus must be conducted through several layers of the cerebral cortex,cerebrospinal fluid (CSF), pia mater , and arachnoid mater before reaching subdural recordingelectrodes placed just below the dura mater (outer cranial membrane).

, ,

( ), mater Pia , mater (

) . However, to reach the scalp electrodes of an electroencephalogram (EEG), electricalsignals must also be conducted through the skull , where potentials rapidly attenuate due to thelow conductivity of bone . ,

(EEG), , . For

this reason, the spatial resolution of ECoG is much higher than EEG, a critical imagingadvantage for presurgical planning. [ 3 ] ECoG offers a temporal resolution of approximately 5 msand a spatial resolution of 1 cm. [ 4 ] , ECOG

EEG, presurgical [3] ECOG 5 ms 1 cm.[4]

Using depth electrodes, the local field potential gives a measure of a neural population in asphere with a radius of 0.5-3 mm around the tip of the electrode. [ 5 ] With a sufficiently highsampling rate (more than about 10 kHz), depth electrodes can also measure action potentials . [ 6 ] In which case the spatial resolution is down to individual neurons, and the field of view of anindividual electrode is approximately 0.05-0.35 mm. [ 5 ] ,

0,5 3 .[5]

( 10 kHz), . [6] ,

, 0,05 - 0,35 mm.[5]

[ edit ] Procedure [ ]


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The ECoG recording is performed from electrodes placed on the exposed cortex. ECOG . In to access the cortex, a surgeon must first perform a craniotomy, removing a part of the skull toexpose the brain surface. ,

,

. This procedure may be performed either under general anesthesia or under local anesthesia if patient interaction is required for functional cortical mapping. ,

.Electrodes are then surgically implanted on the surface of the cortex, with placement guided bythe results of preoperative EEG and magnetic resonance imaging (MRI).

, EEG

(MRI). Electrodes may either be placed outside the dura mater (epidural) or under the dura mater (subdural). ( )

( ). ECoG electrode arrays typically consist of

sixteen sterile, disposable stainless steel, carbon tip, platinum, or gold ball electrodes, eachmounted on a ball and socket joint for ease in positioning. ECOG , , , ,

. These electrodes are attached to anoverlying frame in a crown or halo configuration. [ 7 ] Subdural strip and grid electrodes arealso widely used in various dimensions, having anywhere from 4 to 64 electrode contacts.

.[7], , ,

, 4 64 . The grids are transparent, flexible, and numbered at each electrode contact.

, , . Standard spa between grid electrodes is 1 cm; individual electrodes are typically 5 mm in diameter. Standard

1 ? . The electrodes sit lightly on the cortical surface, and are

designed with enough flexibility to ensure that normal movements of the brain do not causeinjury. ,

. A key advantage of strip and grid electrode arrays is that they may be slid

underneath the dura mater into cortical regions not exposed by the craniotomy.

Strip electrodes and crown arrays may be used in any combination desired.

Depth electrodes may also be used to record activity from deeper structures such as thehippocampus .

, .

[ edit ] D C ES [ ] D C ES


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Direct cortical electrical stimulation (DCES) is frequently performed in concurrence with ECoGrecording for functional mapping of the cortex and identification of critical cortical structures. [ 7 ] When using a crown configuration, a handheld wand bipolar stimulator may be used at anylocation along the electrode array. (DCES)

ECOG

.[7]

, . However, when using a subdural strip, stimulation must be applied

between pairs of adjacent electrodes due to the nonconductive material connecting the electrodeson the grid. , ,

nonconductive . Electrical stimulating currents applied to the cortexare relatively low, between 2 to 4 mA for somatosensory stimulation, and near 15 mA for cognitive stimulation. [ 7 ]

, 2 4 mA , 15 mA .[7]

The functions most commonly mapped through DCES are primary motor, primary sensory, andlanguage. DCES

, , . The patient must be alert andinteractive for mapping procedures, though patient involvement varies with each mapping

procedure. ,

. Language mapping may involve naming, reading aloud, repetition, and oralcomprehension; somatosensory mapping requires that the patient describe sensationsexperienced across the face and extremities as the surgeon stimulates different cortical regions. [ 7] , ,

, ? ,

.[7]

[ edit ] C l inica l app l ications [ ]

Since its development in the 1950's, ECoG has been used to localize epileptogenic zones during presurgical planning, map out cortical functions, and to predict the success of epileptic surgicalresectioning. 1950, ECOG

epileptogenic presurgical , ,

resectioning. ECoG offers several advantages over alternative diagnostic modalities: ECOG :

y Flexible placement of recording and stimulating electrodes [ 2 ] [2]


22/45

y Can be performed at any stage before, during, and after a surgery ,

y Allows for direct electrical stimulation of the brain, identifying critical regions of the cortex to beavoided during surgery ,

y Greater precision and sensitivity than an EEG scalp recording - spatial resolution is higher andsignal-to-noise ratio is superior due to greater proximity to neural activity

-

Limitations of ECoG include: ECOG :

y Limited sampling time seizures ( ictal events) may not be recorded during the ECoG recordingperiod - (ictal )

ECOGy Limited field of view electrode placement is limited by the area of exposed cortex and surgery

time, sampling errors may occur -

, y Recording is subject to the influence of anesthetics, narcotic analgesics, and the surgery itself [ 2 ]

, , [2]

[ edit ] Intractable epilepsy [ ]

Epilepsy is currently ranked as the third most commonly diagnosed neurological disorder,afflicting approximately 2.5 million people in the United States alone. [ 8 ] Epileptic seizures arechronic and unrelated to any immediately treatable causes, such as toxins or infectious diseases,and may vary widely based on etiology, clinical symptoms, and site of origin within the brain.

, 2,5

.[8] , ,

, , , . For patients with intractable epilepsy epilepsy that is unresponsive to

anticonvulsants surgical treatment may be a viable treatment option. - -

.

Extraoperative ECoG Extraoperative ECOG

Before a patient can be identified as a candidate for resectioning surgery, MRI must be performed to demonstrate the presence of a structural lesion within the cortex, supported by EEGevidence of epileptogenic tissue. [ 2 ] Once a lesion has been identified, ECoG may be performedto determine the location and extent of the legion and surrounding irritative region.


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resectioning ,

, EEG epilepto.] [2 , ECOG

. The

EEG, while a valuable diagnostic tool, lacks the precision necessary to localize the epileptogenicregion. , , epileptogenic

ECoG is considered to be the gold standard for assessing neuronal activity in patients withepilepsy, and is widely used for presurgical planning to guide surgical resection of the lesion andepileptogenic zone. [ 9 ] , [ 10 ] The success of the surgery depends on accurate localization andremoval of the epileptogenic zone. ECOG

, presurgical epileptogenic

. [9] , [10] epileptogenic . ECoG data is assessed with regard to ictal spike activity

diffuse fast wave activity recorded during a seizure and interictal epileptiform activity(IEA), brief bursts of neuronal activity recorded between epileptic events. ECOG ictal - "

- interictal (IEA),

. ECoG is also performed following the resectioning surgery todetect any remaining epileptiform activity, and to determine the success of the surgery. ECOG

resectioning ,

. Residual spikes on the ECoG, unaltered by the resection, indicate poor seizurecontrol, and incomplete neutralization of the epileptogenic cortical zone.

ECOG, , , epileptogenic . Additional surgery

may be necessary to completely eradicate seizure activity. .

Intraoperative ECoG ECOG

The objective of the resectioning surgery is to remove the epileptogenic tissue without causingunacceptable neurological consequences. resectioning

epileptogenic . In addition to identifying and localizing the extent of epileptogenic zones, ECoG used

in conjunction with DCES is also a valuable tool for functional cortical mapping. epileptogenic, ECOG DCES

. It is vital to precisely localize critical brain structures, identifyingwhich regions the surgeon must spare during resectioning (the eloquent cortex ) in order to

preserve sensory processing, motor coordination, and speech. , resectioning ( ),


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, , . Functional mapping requires that the patient be able to interact with the surgeon, and thus

is performed under local rather than general anesthesia. , , ,

. Electrical stimulation using cortical and acute depth electrodes is

used to probe distinct regions of the cortex in order to identify centers of speech, somatosensoryintegration, and somatomotor processing.

, , somatomotor. During the resectioning surgery, intraoperative ECoG may also be

performed to monitor the epileptic activity of the tissue and ensure that the entire epileptogeniczone is resectioned. resectioning, ECOG

epileptogenic resectioned

Although the use of extraoperative and intraoperative ECoG in resectioning surgery has been an

accepted clinical practice for several decades, recent studies have shown that the usefulness of this technique may very based on the type of epilepsy a patient exhibits. extraoperative ECOG resectioning

,

. Kuruvilla and Flink reported that while intraoperative ECoG plays a critical role intailored temporal lobectomies, in multiple subpial transections (MST), and in the removal of malformations of cortical development (MCDs), it has been found impractical in standardresection of medial temporal lobe epilepsy (TLE) with MRI evidence of mesial temporalsclerosis (MTS). [ 2 ] A study performed by Wennberg, Quesney, and Rasmussen demonstratedthe presurgical significance of ECoG in frontal lobe epilepsy (FLE) cases. [ 11 ] Kuruvilla flink ECOG

lobectomies, subpial transections (MST), (MCDs),

(TLE) (MTS).[2] Wennberg,

Quesney, Rasmussen presurgical ECOG (FLE) .[11]

[ edit ] Research app l ications [ ]

ECoG has recently emerged as a promising recording technique for use in brain-computer interfaces (BCI). [ 12 ] BCIs are direct neural interfaces that provide control of prosthetic,electronic, or communication devices via direct use of the individual's brain signals. ECOG

- (BCI). [12] BCIs

, , . Brain signals may be recorded either invasively, with


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recording devices implanted directly into the cortex, or noninvasively, using EEG scalpelectrodes. invasively,

, noninvasively, EEG . ECoG serves to provide a partially invasive compromise

between the two modalities while ECoG does not penetrate the blood-brain barrier like

invasive recording devices, it features a higher spatial resolution and higher signal-to-noise ratiothan EEG. ECOG - ECOG -

, EEG. A recent study by Shenoy et al.

Shenoy et. demonstrates the high movement classification accuracy potential of ECoG- based BCIs. [ 12 ] ECOG BCI[12]

[ edit ] Recent advances in E C oG techno logy [ ]

E

CO GThe electrocorticogram is still considered to be the gold standard for defining epileptogeniczones; however, this procedure is risky and highly invasive. electrocorticogram

" " epileptogenic? , . Recent studies have explored the

development of a noninvasive cortical imaging technique for presurgical planning that may provide similar information and resolution of the invasive ECoG.

presurgical EC

In one novel approach, Bin He et al.[ 13 ]

seek to integrate the information provided by astructural MRI and scalp EEG to provide a noninvasive alternative to ECoG. , Bin et al.[13]

MRI EEG ECOG. This study investigated a high-resolution subspace source localization

approach, FINE (first principle vectors) to image the locations and estimate the extents of currentsources from the scalp EEG. subspace

, FINE ( )

. A thresholding technique was applied to the resulting tomography of subspacecorrelation values in order to identify epileptogenic sources.

subspace epileptogenic . This method was tested in three pediatric patients with intractable epilepsy,with encouraging clinical results.

, . Each patiwas evaluated using structural MRI, long-term video EEG monitoring with scalp electrodes, andsubsequently with subdural electrodes.

, EEG , . The ECo


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data was then recorded from implanted subdural electrode grids placed directly on the surface of the cortex. ECOG

. MRI and comptomography images were also obtained for each subject. MRI

.

The epileptogenic zones identified from preoperative EEG data were validated by observationsfrom postoperative ECoG data in all three patients. epileptogenic

EEG ECOG . These preliminary results suggest that it is

possible to direct surgical planning and locate epileptogenic zones noninvasively using thedescribed imaging and integrating methods.

epileptogenic noninvasively . EEG findin

were further validated by the surgical outcomes of all three patients. EEG . After surgical

resectioning, two patients are seizure-free and the third has experienced a significant reduction inseizures. resectioning, -free . Due to its clinical success, FINE offers a

promising alternative to preoperative ECoG, providing information about both the location andextent of epileptogenic sources through a noninvasive imaging procedure.

, FINE ECOG, epileptogenic

.

[ edit ] References [ ]

1. ^ Andre Palmini (200 6). ^ Palmini Andre (200 6). "The concept of the epileptogenic zone: amodern look at Penfield and Jasper's views on the role of interictal spikes'". Epileptic Disorders 8(Suppl 2) : S10 15. epileptogenic : Penfield

Jasper interictal. 8 ( 2): S10-15.

2. ^ a b c d e A. ^ . Kuruvilla, R. Flink (200 3). Kuruvilla, R. flink (200 3). "Intraoperativeelectrocorticography in epilepsy surgery: useful or not?". Seizure 1 2 : 577 58 4. doi :10.101 6/ S105 9-1311(0 3)000 95-5 . "Electrocorticography

: ;". 1 2: 577 -58 4 . doi : 10.101 6/ S105 9-1311 (0 3) 000 95-5 .3. ^ Kimiaki Hashiguchi, Takato Morioka, Fumiaki Yoshida, Yasushi Miyagi, Shinji Nagata, Ayumi

Sakata, Tomio Sasaki (200 7). ^ Kimiaki Hashiguchi, Takato Morioka, Fumiaki , Miyagi

Yasushi, Shinji Nagata, Ayumi Sakata, Tomio Sasaki (200 7). "Correlation between scalp-recordedelectroencephalographic and electrocorticographic activities during ictal period". Seizure 16 :238 247 . doi : 10.101 6/ j.seizure.200 6.12.010 . " ,

electrocorticographic ictal".16 :238-2 47 . doi : 10.101 6/ j.seizure.200 6 .12.010 .

4. ^ Eishi Asano, Csaba Juhasz, Aashit Shah, Otto Muzik, Diane C. Chugani, Jagdish Shad, SandeepSood, Harry T. Chugani (2005). ^ Eishi Asano, Csaba Juhsz, Aashit Shah, Otto Muzik, Diane .Chugani, Jagdish shad, Sood Sandeep, Harry T. Chugani (2005). "Origin and Propagation of


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Epileptic Spasms Delineated on Electrocorticography". Epilepsia 46 : 108 6 10 97 . doi :10.1111 / j.1528-11 67 .2005.05205.x .

Electrocorticography".Epilepsia 46 : 108 6-10 97 . doi : 10.1111 / j.1528-11 67 .2005.05205.x .

5. ^ a b Nikos K. Logothetis (200 3). ^ . (2003). "The underpinning of the BOLDfunctional magnetic resonance imaging signal". Journal of Neuroscience 23 : 3963 397 1.

BOLD . Journal of Neuroscience 23: 3963 -397 1.

6. ^ Istvan Ulbert, Eric Halgren, Gary Heit, George Karmos (2001). ^ Ulbert Istvan, Eric Halgren,Gary Heit, Karmos (2001). "Multiple microelectrode-recording system for humanintracortical applications". Journal of Neuroscience Methods 106 : 69 79 . doi : 10.101 6/ S0165-02 70(01)00 33 0-2 . " - intracortical ". Journal of Neuroscience 106 : 69 -79 . doi : 10.101 6/ S0165-02 70 (01) 00 33 0 - 2 .

7. ^ a b c d L. ^ L. Schuh, I. Drury (1 996 ). Schuh, . Drury (1 996 ). "IntraoperativeElectrocorticography and Direct Cortical Electrical Stimulation". Seminars in Anesthesia 16 : 46 55. " Electrocorticography Direct .

16 : 46 -55.8. ^ Michael Kohrman (200 7). ^ Michael Kohrman (200 7). "What is Epilepsy? Clinical Perspectives

in the Diagnosis and Treatment". Journal of Clinical Neurophysiology 24 : 87 95. doi :10.10 97/ WNP.0b01 3e 3180 415b51 . " ;

. 24: 87-95. doi :10.10 97/ WNP.0b01 3e 3180 415b51 .

9. ^ Hidenori Sugano, Hiroyuki Shimizu, Shigeki Sunaga (200 7). ^ Hidenori Sugano, HiroyukiShimizu, Shigeki Sunaga (200 7). "Efficacy of intraoperative electrocorticography for assessingseizure outcomes in intractable epilepsy patients with temporal-lobe-mass lesions". Seizure 16 :120 12 7 . doi : 10.101 6/ j.seizure.200 6.10.010 . electrocorticography

, - . 16 : 120-12 7 . doi :10.101 6/ j.seizure.200 6.10.010 .10. ^ Kai J. Miller, Marcel denNijs, Pradeep Shenoy, John W. Miller, Rajesh PN Rao, Jeffrey G.

Ojemann (200 7). ^ Kai J. Miller, Marcel denNijs, Pradeep Shenoy, John W. Miller, Rajesh PN Rao,Jeffrey . Ojemann (200 7). "Real-time functional brain mapping using electrocorticography".NeuroImage 37 : 50 4 507 . doi : 10.101 6/ j.neuroimage.200 7 .05.02 9 . "

electrocorticography".NeuroImage 37: 50 4-50 7. doi : 10.101 6/ j.neuroimage.200 7 .05.02 9 .

11. ^ R. ^ R. Wennberg, F. Quesney, A. Olivier, T. Rasmussen (1 99 8). Wennberg, F. Quesney, A.Olivier, T. Rasmussen (1 99 8). "Electrocorticography and outcome in frontal lobe epilepsy".Electroencephalography and Clinical Neurophysiology 106 : 357 36 8. doi : 10.101 6/ S001 3-4694 (97 )001 48-X . "Electrocorticography .

106 : 357-36 8. doi : 10.101 6/ S001 3-4694 (97 ) 001 48-X .

12. ^ a b Pradeep Shenoy, Kai J. Miller, Jeffrey G. Ojemann, Rajesh PN Rao (200 7) (PDF). Generalized Features for Electrocorticographic BCIs .http: // www.cs.washington.edu / homes / pshenoy / papers / ecogclassif_tbme0 7preprint.pdf . ^ Pradeep Shenoy, Kai J. Miller, Jeffrey . Ojemann, Rajesh PN Rao (200 7) (PDF).

Electrocorticographic BCIs .http: // www.cs.washington.edu / homes / pshenoy / papers / ecogclassif_tbme0 7preprint.pdf .


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13 . ^ Lei Ding, Christopher Wilke, Bobby Xu, Xiaoliang Xu, Wim van Drongelen, Michael Kohrman,Bin He (200 7). ^ Ding Lei, Wilke Christopher, Xu Bobby, Xiaoliang Xu, Wim van Drongelen,Michael Kohrman, Bin (200 7). "EG source imaging: correlating source locations andextents with electrocorticography and surgical resections in epilepsy patients". Journal of Clinical Neurophysiology 24 : 130 136 . doi : 10.10 97/ WNP.0b01 3e 3180 38fd52 . "

EG: electrocorticography resections ". 24: 130-1 36 . doi :10.10 97/ WNP.0b01 3e 3180 38fd52 .

[ edit ] S ee a lso [ ] y Wilder Penfield Penfield y Herbert Jasper Herbert Jasper y epilepsy y electroencephalogram y Magnetic Resonance Imaging y

BCI BCI y FINE- first principle vectors (combination of EEG and MRI for non-invasive alternative to

intracranial EEG (icEEG)) FINE- (

EEG(icEEG))

[ edit ] Ex terna l l inks [ ] y Teenager moves video icons just by using mind electrocorticographic activity .

electrocorticographic .

[hide ]

v d e v

Bra in com put e r in te rfa ce Bra in-Com put e r In te rfa ce

Technologies

Biomechatronics Brain implant BrainGate Brainport Cyberware Exocortex Intelligence amplification Isolated brain Neuroprosthetics Neurotechnology Optogenetics Sensorysubstitution Synthetic telepathy Biomechatronics

BrainGate Brainport Cyberware Exocortex Intelligence Neuroprosthetics

Optogenetics Sensory

ScientificPhenomena

Elec tr oco rt icog rap hy (ECoG) Neural ensemble Neuroplasticity Elec tr oco rt icog rap hy (ECOG) neuroplasticity


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DisciplinesCognitive science Cognitive neuroscience Computationalneuroscience NBIC Neural engineering Neuroscience

NBIC

Speculative Cyborg Mind uploading Whole-body transplant Mind

People

Charles Stross Douglas Engelbart Hugh Herr JCR Licklider KevinWarwick Matt Nagle Merlin Donald Miguel Nicolelis Peter Kyberd Steve Mann Vernor Vinge Yoky Matsuoka Charles Stross DouglasEngelbart JCR Licklider Kevin Warwick Matt Nagle Merlin Donald Miguel Nicolelis Peter Kyberd Steve Mann VernorVinge Yoky Matsuoka

Other Human enhancement Mind control Neurohacking Simulated reality Transhumanism Mind Neurohacking Transhumanism

Retrieved from " http: // en.wikipedia.org / wiki/ Electrocorticography " "http: // en.wikipedia.org / wiki/ Electrocorticography "Categories : Neurology | Medical tests | Electrophysiology | Neurophysiology | Neurotechnology |Brain-computer interfacing : | | |

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From Wikipedia, the free encyclopedia , Jump to: navigation , search : ,

This article includes a list of references , related reading or external links , but its s our ce s rem a in unc lear b ec aus e it la cks in line citat ion s . Please improve this article by introducing more precisecitations where appropriate . ( March 2009)

, , , in line citat ion s .

. ( 2009)

El ectrophysio logy (from Greek , lektron , "amber" [see the etymology of "electron" ]; , physis , "nature, origin"; and - , -logia ) is the study of the electrical properties of

biological cells and tissues. ( , lektron, [ . "electron"]? , Physis, " , "? -

,- ) .It involves measurements of voltage change or electric current on a wide variety of scales fromsingle ion channel proteins to whole organs like the heart .

. In neuroscience , it includes measurements of

the electrical activity of neurons , and particularly action potential activity. , ,

. Recordings of large-scale electric signals from the nervous system suchas electroencephalography , may also be referred to as electrophysiological recordings [ 1 ] .

, ,

[1] .


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"Current Clamp" is a common technique in electrophysiology. "Current Clamp" . This is a whole-cell current clamp recording of a neuron firing due to it being

depolarized by current injection depolarized

N euroscience portal

C ontents

[hide ]

y 1 Definition and scope 1 o 1.1 Classical electrophysiological techniques 1,1 o 1.2 Optical electrophysiological techniques 1,2

y 2 Intracellular recording 2

o 2.1 Voltage clamp 2,1 o 2.2 Current clamp 2.2 o 2.3 The patch-clamp technique 2,3 patch-clamp o 2.4 Sharp electrode technique 2,4 Sharp

y 3 Extracellular recording 3 o 3.1 Single-unit recording 3,1 Single- o 3.2 Field potentials 3 .2 o 3.3 Amperometry 3,3 Amperometry

y 4 Planar patch clamp 4 patch Planar y 5 The Bioelectric Recognition Assay (BERA) 5 (Bera) y 6 Reporting guidelines for electrophysiology experiments 6

y 7 See also 7 y 8 References 8 y 9 External links 9

[ edit ] Definition and scope [ ]

[ edit ] Classical electrophysiological techniques [ ]

Electrophysiology is the science and branch of physiology that pertains to the flow of ions in biological tissues and, in particular, to the electrical recording techniques that enable themeasurement of this flow.

, . Class

electrophysiology techniques involve placing electrodes into various preparations of biological


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tissue. . The principal types of electrodes are: 1) simple

solid conductors, such as discs and needles (singles or arrays, often insulated except for the tip),2) tracings on printed circuit boards, also insulated except for the tip, and 3) hollow tubes filledwith an electrolyte, such as glass pipettes filled with potassium chloride solution or another

electrolyte solution. : 1) , ( , , , 3)

, . The principal preparations include 1) living organisms, 2) excised

tissue (acute or cultured), 3) dissociated cells from excised tissue (acute or cultured), 4)artificially grown cells or tissues, or 5) hybrids of the above.

1) , 2) ( ), 3) ( ), 4)

, 5) .

If an electrode is small enough (micrometers) in diameter, then the electro-physiologist maychoose to insert the tip into a single cell. ( ) , -

. Such a configuration allows direct observation and recording of the intracellular electrical activity of a single cell.

. However, atsame time such invasive setup reduces the life of the cell and causes a leak of substances acrossthe cell membrane. , setup

. Intracellular activity may also be observed using a specially formed (hollow) glass pipette containing anelectrolyte.

( ) . In thistechnique, the microscopic pipette tip is pressed against the cell membrane, to which it tightlyadheres by an interaction between glass and lipids of the cell membrane. ,

,

electrolyte within the pipette may be brought into fluid continuity with the cytoplasm bydelivering a pulse of pressure to the electrolyte in order to rupture the small patch of membraneencircled by the pipette rim ( whole-cell recording ).

, patch

( ). Alternatively, ionic continuity may beestablished by "perforating" the patch by allowing exogenous pore-forming agent within theelectrolyte to insert themselves into the membrane patch ( perforated patch recording ).

, , -

patch ( patch). Finally, the patch may beleft intact ( patch recording ). , ( patch ).


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The electrophysiologist may choose not to insert the tip into a single cell. electrophysiologist . Instead, the electrode tip may

be left in continuity with the extracellular space. ' , . If the tip is small enough, such a configuration

may allow indirect observation and recording of action potentials from a single cell, and is

termed single-unit recording . , , . Depending on the preparation and precise

placement, an extracellular configuration may pick up the activity of several nearby cellssimultaneously, and this is termed multi-unit recording .

, ,

multi- .

As electrode size increases, the resolving power decreases. , . Larger electrodes are sensitive only to the net activity of many

cells, termed local field potentials . , . Still larger electrodes, such as uninsulated needles and surface electrodes used by clinical and surgicalneurophysiologists, are sensitive only to certain types of synchronous activity within populationsof cells numbering in the millions. ,

,

.

Other classical electrophysiological techniques include single channel recording andamperometry .

amperometry .

[ edit ] Optical electrophysiological techniques [ ]

Optical electrophysiological techniques were created by scientists and engineers to overcomeone of the main limitations of classical techniques.

. Classical techniques allow observation of

electrical activity at approximately a single point within a volume of tissue.

. Essentially, classical techniques singularize a distributed phenomenon. , . Interest in the spatial distribution of bioelectric activity prompted development of molecules capable of emitting light in response totheir electrical or chemical environment.

. Examples arevoltage sensitive dyes

and fluoresceing proteins. fluoresceing.


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After introducing one or more such compounds into tissue via perfusion, injection or geneexpression, the 1 or 2-dimensional distribution of electrical activity may be observed andrecorded.

, 1 2- .

This section requires expansion . .

Many particular electrophysiological readings have specific names: :

y Electrocardiography - for the heart - y Electroencephalography - for the brain - y Electrocorticography - from the cerebral cortex Electrocorticography -

y

Electromyography - for the muscles - y Electrooculography - for the eyes Electrooculography - y Electroretinography - for the retina Electroretinography - y Electroantennography - for the olfactory receptors in arthropods Electroantennography -

y Audiology - for the auditory system -

[ edit ] Intrace ll u lar recording [ ]

Intrace ll u lar recording involves measuring voltage and/or current across the membrane of acell. /

. To make an intracellular recording, the tip of a fine (sharp)microelectrode must be inserted inside the cell, so that the membrane potential can be measured.

, ( ,

. Typically, the resting membrane potential of a healthy cell will be -60 to -80mV, and during an act ion potential the membrane potential might reach +40 mV. ,

-60 -80 mV, 40 mV. In

Alan Lloyd Hodgkin and Andrew Fielding Huxley won the Nobel Prize in Physiology or Medicine for their contribution to understanding the mechanisms underlying the generation of action potentials in neurons. 1963, Alan Lloyd Hodgkin Andrew Fielding

. Their

experiments involved intracellular recordings from the giant axon of Atlantic squid (Loligo pealei), and were among the first applications of the "voltage clamp" technique.

(Loligo pealei), "


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Today, most microelectrodes used for intracellular recording are glass micropipettes, with a tipdiameter of < 1 micrometre, and a resistance of several megaohms. , microelectrodes

1


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The voltage clamp technique allows an experimenter to "clamp" the cell potential at a chosenvalue. " "

. This makes it possible to measure how muchionic current crosses a cell's membrane at any given voltage.

. This is important

because many of the ion channels in the membrane of a neuron are voltage gated ion channels ,which open only when the membrane voltage is within a certain range.

, Voltage clamp measurements of current are made possible by the near-simultaneous digitalsubtraction of transient capacitive currents that pass as the recording electrode and cellmembrane are charged to alter the cell's potential.

. (See main article onvoltage clamp .)( .)

[ edit ] Current clamp [ ]

The current clamp technique records the membrane potential by injecting current into a cellthrough the recording electrode.

. Unlike in thevoltage clamp mode, where the membrane potential is held at a level determined by theexperimenter, in "current clamp" mode the membrane potential is free to vary, and the amplifier records whatever voltage the cell generates on its own or as a result of stimulation.

, , " " mode

, . This technique is used tostudy how a cell responds when electric current enters a cell; this is important for instance for understanding how neurons respond to neurotransmitters that act by opening membrane ionchannels .

? ,

.

Most current-clamp amplifiers provide little or no amplification of the voltage changes recordedfrom the cell.

. The "amplifier" is actuallyan electrometer , sometimes referred to as a "unity gain amplifier"; its main job is to change thenature of small signals (in the mV range) produced by cells so that they can be accuratelyrecorded by low- impedance electronics. " " electrometer , " "?

( mV) , -

. The amplifier increases the current behind the signal while decreasing the


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resistance over which that current passes. , . Consider this example based o

Ohm's law: a voltage of 10 mV is generated by passing 10 nanoamperes of current across 1 M of resistance. Ohm: 10 mV

10nanoamperes 1M . The

electrometer changes this "high impedance signal" to a "low impedance signal" by using avoltage follower circuit. " " " ", . A voltage follower reads the voltage on the input (caused by a small current through a big resistor ).

( ). It then instructs a parallel circuit that has a large current source behind it

(the electrical mains) and adjusts the resistance of that parallel circuit to give the same outputvoltage, but across a lower resistance.

( ) , .

[ edit ] The patch-clamp technique [ ] patch-clamp

The cell-attached patch clamp uses a micropipette attached to the cell membrane to allow recordingfrom a single ion channel. - patch

.

Main article: Patch clamp :Patch

This technique was developed by Erwin Neher and Bert Sakmann who received the Nobel Prizein 1991 [ 2 ] . Erwin Neher Bert Sakmann

1991[2] . Conventional intracellular recording involves impaling a cellwith a fine electrode; patch-clamp recording takes a different approach.

impaling ? Patchclamp . A patch-clamp microelectrode is amicropipette with a relatively large tip diameter. patch-clamp

. The microelectrode is placed next to a cell,and gentle suction is applied through the microelectrode to draw a piece of the cell membrane(the 'patch') into the microelectrode tip; the glass tip forms a high resistance 'seal' with the cellmembrane. , ,


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) ? . This configuration is the "cell-attached" mode, and itcan be used for studying the activity of the ion channels that are present in the patch of membrane. -attached" ,

patch . If more suction is now applied, the small patch of membrane in theelectrode tip can be displaced, leaving the electrode sealed to the rest of the cell. ,

, . This "whole-cell" mode allows very stable intracellular recording. " " mode . A

disadvantage (compared to conventional intracellular recording with sharp electrodes) is that theintracellular fluid of the cell mixes with the solution inside the recording electrode, and so someimportant components of the intracellular fluid can be diluted. (

) ,

. A variant of this techniquthe "perforated patch" technique, tries to minimise these problems. , ,

Instead of applying suction to displace the membrane patch from the electrode tip, it is also possible to make small holes on the patch with pore-forming agents so that large molecules suchas proteins can stay inside the cell and ions can pass through the holes freely.

patch , , ,

. Also the patch of membrane

can be pulled away from the rest of the cell. , patch . This approach enables the membrane

properties of the patch to be analysed pharmacologically. patch .

[ edit ] Sharp electrode technique [ ] Sharp

In situations where one wants to record the potential inside the cell membrane with minimaleffect on the ionic constitution of the intracellular fluid a sharp electrode can be used.

. These micropipets (electrodes) are again likethose for patch clamp pulled from glass capillaries, but the pore is much smaller so that there isvery little ion exchange between the intracellular fluid and the electrolyte in the pipette. micropipets ( ) patch clamp

, , . Th

resistance of the electrode in 10s or 100s of M in this case. 10s 100s M . Often the tip of the electrode is filled with variouskinds of dyes like Lucifer yellow to fill the cells recorded from, for later confirmation of their


39/45

morphology under a microscope. , , Lucifer ,

, . The dyes areinjected by applying a positive or negative, DC or pulsed voltage to the electrodes depending onthe polarity of the dye. , , DC

, .

[ edit ] Ex trace ll u l ar recording [ ]

[ edit ] Single-unit recording [ ] Single- Main article: single-unit recording :single-

An electrode introduced into the brain of a living animal will detect electrical activity that isgenerated by the neurons adjacent to the electrode tip.

. If the electrode is a microelectrode, with a tipsize of about 1 micrometre, the electrode will usually detect the activity of at most one neuron.

, 1 , . Recording in this way is

generally called "single-unit" recording. " . The action potentials recorded are very like the

action potentials that are recorded intracellularly, but the signals are very much smaller (typicallyabout 1 mV).

, ( 1 mV). Most recordings of the activity of single neurons in anesthetized animals are

made in this way, and all recordings of single neurons in conscious animals. ,

. Recordings of single neurons in living animals have providedimportant insights into how the brain processes information.

. For example,David Hubel and Torsten Wiesel recorded the

activity of single neurons in the primary visual cortex of the anesthetized cat, and showed howsingle neurons in this area respond to very specific features of a visual stimulus [ 3 ] [ 4 ] .

, David Hubel Torsten Wiesel ,

[3] [4] . Hubel and Wiesel were awarded the Nobel Prize in Physiology or Medicinein 1981 [ 5 ] . Hubel Wiesel 1981 [5] . If the electrode tip is slightly larger, then the electrode might record the activitygenerated by several neurons. ,

. This tyrecording is often called "multi-unit recording", and is often used in conscious animals to recordchanges in the activity in a discrete brain area during normal activity.


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(# 1) .

Extracellular field potentials are local current sinks or sources that are generated by the collectiveactivity of many cells.

. Usually a fiel potential is generated by the simultaneous activation of many neurons by synaptic transmission .

. The diagram to the right shows hippocampal synaptic field potentials. . At right, the lower trace shows a negative wave that corresponds to a current sink caused by positivecharges entering cells through postsynaptic glutamate receptors , while the upper trace shows a

positive wave that is generated by the current that leaves the cell (at the cell body) to completethe circuit. , ,

,

( ) . For more information, see local field potential . , .

[ edit ] Amperometry [ ] Amperometry

Amperometry uses a carbon electrode to record changes in the chemical composition of theoxidized components of a biological solution. Amperometry

. Oxidation and reduction is accomplished by changing the voltage at the active

surface of the recording electrode in a process known as "scanning".

" ". Because certain brain chemicals

lose or gain electrons at characteristic voltages, individual species can be identified.

, , . Amperometry has been used for studyingexocytosis in the neural and endocrine systems. Amperometry exocytosis . Many monoamineneurotransmitters , eg,norepinephrine (noradrenalin), dopamine , serotonin (5-HT), are oxidizable.

, . ., ( ), , (5-HT), . The method can also be used with cells that do not

secrete oxidizable neurotransmitters by "loading" them with 5-HT or dopamine.

" 5- .

[ edit ] P lanar patch c lamp [ ] patchP lanar


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P lanar patch c lamp is a novel method developed for high throughput electrophysiology.

. Instead of positioning a pipette on an adherent cell, cellsuspension is pipetted on a chip containing a microstructured aperture.

,

.

Schematic drawing of the classical patch clamp configuration. patch. The patch pipette is moved to the cell using a micromanipulator under

optical control. . Relative movements between the pipette and the cell have to be

avoided in order to keep the cell-pipette connection intact.

.

In planar patch configuration the cell is positioned by suction - relative movements between cell andaperture can then be excluded after sealing. patch

-

. An Antivibration table is not necessary. .


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A single cell is then positioned on the hole by suction and a tight connection (Gigaseal) isformed.

(Gigaseal) . The planar geometry offers a variety of advantagescompared to the classical experiment: - it allows for integration of microfluidics , which enablesautomatic compound application for ion channel screening.

: - ,

. - the system is accessible for optical or scanning probe techniques - perfusion of the intracellular side can be performed. -

- .

[ edit ] The Bioe lectric Recognition Assay (B E RA) [ ]

(Bera)

The Bioe lectric Recognition Assay (B E RA) is a novel method for measuring changes in themembrane potential of cells immobilized in a gel matrix. The

(Bera) . Apart from the increased stability

of the electrode-cell interface, immobilization preserves the viability and physiological functionsof the cells. - ,

. B primary used in biosensor applications in order to assay analytes which can interact with theimmobilized cells by changing the cell membrane potential. Bera

.

In this way, when a positive sample is added to the sensor, a characteristic, 'signature-like'change in electrical potential occurs. , , , -

. BERA has been used for the detection for human viruses (Hepatitis Band C viruses, herpes viruses) and veterinary disease agents (foot and mouth disease virus,

prions, blue tongue virus) and plants (tobacco and cucumber viruses) in a highly specific, rapid(12 minutes), reproducible and cost-efficient fashion. Bera

( B C , )


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( , , ) ( ) , (1-2 )

. The method has also been used for thedetection of environmental toxins, such as herbicides and the determination of very lowconcentrations of superoxide anion in clinical samples.

, . A recent advance in the evolutionof the BERA technology was the development of a technique called M olecu lar Identificationthrough M embrane E ngineering ( M IM E ) .

Bera (M IM E ). This technique allows for building cells with absolutely

defined specificity against virtually any molecule of interest, by embedding thousand of artificialreceptors into the cell membrane.

, .

[ edit ] Reporting guide l ines for e lectrophysio logyex periments [ ]

This section con ta in s t oo m uch jar gon and may need simplification or further explanation.

. Please discuss this issue on the talk page , and / or remove or explain jargon termsused in the article. Editing help is available. ( April 2009)

, / . .( 2009)

Minimum Information (MI) standards or reporting guidelines specify the minimum amount of meta data (information) and data required to meet a specific aims or aims.

(MI) ( )

. Usually the aim is to provide enoughmeta data and data to enable the unambiguous reproduction and interpretation of an experiment.

. MI guidelines are normally

informal human readable specifications that inform the development of formal data models (egXML or UML ), data exchange formats (eg FuGE , MAGE-ML, MAGE-TAB) or knowledgemodels such as an ontology (eg OBI , MGED-Ontology). MI

( . .XML UML ),

( . ., , MAGE-ML, MAGE- ) , ( . . . . . , MGED - ).


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The Minimum Information about a Neuroscience investigation (MINI) family of reportingguideline documents, produced by community consultation and continually available for publiccomment aims to provide a consistent set of guidelines in order to report an electrophysiologyexperiment. ( )

documents ,

. A MINI module represents the minimum information that should be

reported about a dataset to facilitate computational access and analysis to allow a reader tointerpret and critically evaluate the processes performed and the conclusions reached, and tosupport their experimental corroboration. MINI

, . In practice a MINI module comprises a checklist of information

that should be provided (for example about the protocols employed) whena data set is described

for publication. , MINI ( ) whena . The full specification of the

MINI module can be found here [ 6 ] . MINI [6] .

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