Actividad neuronal en el sistema auditivo: potenciales provocados y

unidades

Prof. Ricardo A. Velluti MD, DSc

Neuro-Otología Experimental y Sueño

Otorrinolaringología (ORL), Hospital de Clínicas

Programa de Desarrollo de Ciencias Básicas (Pedeciba) y ANII. Universidad de la República. Montevideo, Uruguay

ricardo.velluti@gmail.com

Shannon, 1948; 1949Shannon, 1948; 1949

IInformation theory makes sense only if the nformation theory makes sense only if the “receiver” of signals knows the full range of “receiver” of signals knows the full range of possibilities.possibilities.

(Information transmitted in Morse code can be usefull only if (Information transmitted in Morse code can be usefull only if the “receiver” knows that code)the “receiver” knows that code)

Information is carried out by :Information is carried out by :

1. Amplitude and waveform of evoked activity1. Amplitude and waveform of evoked activity

2. Neuronal firing rate (how the brain can 2. Neuronal firing rate (how the brain can measure “the firing rate”?measure “the firing rate”?

3. A response to a transient stimulus my be carried 3. A response to a transient stimulus my be carried out by the first spike or twoout by the first spike or two

4. Temporal distribution of the neuronal firing, 4. Temporal distribution of the neuronal firing, pattern of dischargepattern of discharge

5. Relationships with other brain rhythms5. Relationships with other brain rhythms

Information ProcessingCell Assemblies/Neuronal Networks

La actividad neuronal puede expresarse a través La actividad neuronal puede expresarse a través de diversas tecnologíasde diversas tecnologías

• 1. Registro de la actividad de campo cercano:1. Registro de la actividad de campo cercano:

- Potenciales Provocados- Potenciales Provocados

- Potenciales Provocados de campo lejano- Potenciales Provocados de campo lejano• 2. Descargas neuronales: 2. Descargas neuronales:

- con registros intracelulares- con registros intracelulares

- con registros extracelulares- con registros extracelulares• 3. Magnetoencefalografía (MEG) Actividad provocada3. Magnetoencefalografía (MEG) Actividad provocada• 4. Resonancia Magnética Funcional (fMRI)4. Resonancia Magnética Funcional (fMRI)• 5. Tomografía por Emisión de Positrones (PET)5. Tomografía por Emisión de Positrones (PET)

A

B

Averaged Human Auditory Evoked PotentialsAveraged Human Auditory Evoked Potentials

A.A. WakefulnessWakefulness

B. SleepB. Sleep

García-Austt et al. 1961García-Austt et al. 1961

El sistema Auditivo El sistema Auditivo Funciona 24 horas.Funciona 24 horas.

Auditory nerve Auditory nerve compoundcompound

action potentials action potentials

HABITUATIONHABITUATION

Buño, Velluti, Handler, García-Austt, 1966Buño, Velluti, Handler, García-Austt, 1966

Vía Auditiva AscendenteVía Auditiva Ascendente

Vía Auditiva Descendente (Eferente)Vía Auditiva Descendente (Eferente)

Cochlear nucleus post-stimulus time histogramsCochlear nucleus post-stimulus time histograms

A B

C D

0 40 ms

Toneburst

WAKEFULNESS

Histogramas Post EstímulosHistogramas Post Estímulos

Fig 5.4.

Cortical Auditory Evoked Potentials Cortical Auditory Evoked Potentials in Ratin Rat

Hall and Borbély, 1970Hall and Borbély, 1970

Local-field and Far-field auditory evoked Local-field and Far-field auditory evoked potentialspotentials

CN 20 V

SO le ft SO right

IC

M G

Acx

A B

1 ms

Velluti, Galambos 1967

Velluti 2008

Guerit 1993

Tumor de Fosa Posterior derecha, Bulbo y ProtuberanciaGuerit, 1993

Potenciales Provocados de

Tronco Cerebral

Muerte cerebral

Chiappa 1997

…but the brain is also able to be in different states – called asleep,

awake, or dreaming – involving changes like receiving sensory

information that are not necessarily structural, rather

functional.

Thus, it is still possible that learning mechanisms

are ascribed to the dynamic, emergent properties of neural

ensembles. We have more neurons than proteins, and perhaps

the former can carry out a good job without the need of any

structural modifications of their already sophisticated connectivity.

Why, then, do most neuroscientists prefer to lean on

neural plasticity rather than on neural functional states?

J.M. Delgado García, 2008J.M. Delgado García, 2008In: Velluti, 2008 The Auditory In: Velluti, 2008 The Auditory System in Sleep, pp 135-136.System in Sleep, pp 135-136.

A HUB neuron:A HUB neuron:

In adults tends to inhibit the activity of the recipient neuron, though in In adults tends to inhibit the activity of the recipient neuron, though in

developing networks, GABA has excitatory effects.  They also have very developing networks, GABA has excitatory effects.  They also have very

extensive axonal arborisations – they project over larger distances and make a extensive axonal arborisations – they project over larger distances and make a

greater number of and stronger synaptic connections than non-hub neurons. greater number of and stronger synaptic connections than non-hub neurons.

Finally, they are also more responsive to inputs and quicker to fire action Finally, they are also more responsive to inputs and quicker to fire action

potentials themselves, placing them in a position to orchestrate the responses potentials themselves, placing them in a position to orchestrate the responses

of the entire network. of the entire network. 

Though hub neurons have so far only been observed in the hippocampus it Though hub neurons have so far only been observed in the hippocampus it

seems almost certain that they will also be found in the cortex, where their seems almost certain that they will also be found in the cortex, where their

effects may be fundamental for the information processing capabilities of the effects may be fundamental for the information processing capabilities of the

brain.  brain. 

Bonifazi, P., Goldin, M., Picardo, M., Jorquera, I., Cattani, A., Bianconi, G., Represa, A., Bonifazi, P., Goldin, M., Picardo, M., Jorquera, I., Cattani, A., Bianconi, G., Represa, A.,

Ben-Ari, Y., &Cossart, R. (2009). Ben-Ari, Y., &Cossart, R. (2009). GABAergic Hub Neurons Orchestrate Synchrony in GABAergic Hub Neurons Orchestrate Synchrony in

Developing Hippocampal Networks Developing Hippocampal Networks Science, 326Science, 326 (5958), 1419-1424 DOI (5958), 1419-1424 DOI

Auditory Cortex fMRI Auditory Cortex fMRI (Portas et al. 2005)(Portas et al. 2005)

Fig 6.4.

MagnetoencephalographyMagnetoencephalography

Cortical Auditory Evoked ActivityCortical Auditory Evoked Activity

Kakigi et al. 2003

Redes Neuronales, Redes Neuronales, Sueño y AudiciónSueño y Audición

MAGNETOENCEPHALOGRAPHIC MAGNETOENCEPHALOGRAPHIC EVOKED ACTIVITYEVOKED ACTIVITY

Kakigi et al. Sleep Med. (2003) Kakigi et al. Sleep Med. (2003)

Getting 1989

McGinty 2005

Peña et al. 1999; Velluti, 2005

Pre-Optic Region UnitPre-Optic Region Unit

Cortical auditory unitsCortical auditory units

Events - related potentials to words

Bastuji and García-Larrea, 2005

Bastuji, Garcia-Larrea 2005

Wave P300Wave P300

WakefulnessWakefulness

Sleep stagesSleep stages

““Mismatch Negativity (MMN)”Mismatch Negativity (MMN)”

MMN is a negative potential appearing between 100 and 200 ms MMN is a negative potential appearing between 100 and 200 ms as a consequence of any variation in a repetitive stream of as a consequence of any variation in a repetitive stream of stimuli. Its generators are in the superior temporal plane of the stimuli. Its generators are in the superior temporal plane of the auditory cortex (review, Alho et al., 1995) with the addition of a auditory cortex (review, Alho et al., 1995) with the addition of a frontal component (Giard et al., 1990).frontal component (Giard et al., 1990).

Extracellular recording system duringWakefulness and Sleep

Guinea pig partially restrained ready forrecording

Auditory Cortical (A1Auditory Cortical (A1) Neuron) Neuron

Velluti, Peña, Pedemonte, 2000

Cortical influences Cortical influences on Inferior on Inferior Colliculus Colliculus Auditory NeuronAuditory Neuron

Goldstein-Daruech, Goldstein-Daruech,

Pedemonte, Inderkum, VellutiPedemonte, Inderkum, Velluti

Hearing Res. 2002Hearing Res. 2002

Normal and Inverted Guinea Pig Natural Call StimuliNormal and Inverted Guinea Pig Natural Call StimuliAuditory Cortical (A1) RecordingAuditory Cortical (A1) Recording

Pérez-Perera, Velluti. Actas de Fisiología 2001

Actividad Neuronal Unitaria IntracelularActividad Neuronal Unitaria Intracelular

Inferior Colliculus Auditory NeuronInferior Colliculus Auditory Neuron

Functional Magnetic Resonance Imaging Functional Magnetic Resonance Imaging (fMRI)(fMRI)

1.1. When elements as the Hydrogen is exposed to a strong static When elements as the Hydrogen is exposed to a strong static magnetic field, the nuclei develop a net alignement in the magnetic field, the nuclei develop a net alignement in the direction of the applied fielddirection of the applied field

2.2. A brief pulse of radio waves provide energy then the nuclei emit A brief pulse of radio waves provide energy then the nuclei emit radio wavesradio waves

3.3. The resonating nuclei thus became radio waves transmitters The resonating nuclei thus became radio waves transmitters

4.4. The frequency of the radio waves is different in different The frequency of the radio waves is different in different chemical or physical environmentchemical or physical environment

Positron Emission Tomography (PET) Positron Emission Tomography (PET) Imaging of Brain ActivityImaging of Brain Activity

1.1. A radioactive solution is introduced into the bloodstreamA radioactive solution is introduced into the bloodstream

2.2. The radioactive substance emit positrons (electrons positively The radioactive substance emit positrons (electrons positively

charged) producing photons of lightcharged) producing photons of light

3.3. Neurons normally use glucose in their metabolism. Neurons normally use glucose in their metabolism. The 2-The 2-

deoxyglucose is takendeoxyglucose is taken and its amount is proportional to their acyivity and its amount is proportional to their acyivity

4.4. Thus, the number of positron emissions indicate the neuron´s level of Thus, the number of positron emissions indicate the neuron´s level of

activityactivity

5.5. Limitations: spatial resolution is only 5-10 mm; takes from 1 to many Limitations: spatial resolution is only 5-10 mm; takes from 1 to many

minutes to obtain; shows the activity of many thousands of neuronsminutes to obtain; shows the activity of many thousands of neurons

Phrenology (Gall 1792)1. Phrenology is based on

the concept that the brain is the organ of the mind, and that certain brain areas have localized, specific functions or modules

2. 2.Phrenologists believed that the mind has a set of different mental faculties, with each particular faculty represented in a different area of the brain.

3. …so that a person's capacity for a given personality trait could be determined simply by measuring the area of the skull that overlies the corresponding area of the brain.