1_brain imaging techniques

7/25/2019 1_Brain Imaging Techniques

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Biological Bases of Behaviour.Lecture 7: Techniques for

Understanding Brain Structure& Function.

Kalat (2!


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Learning #utco$es.

%t the end of this lecture ou should 'e a'le to:

. )escri'e a range of techniques used to deter$ine

'rain structure and function. 2. List the advantages and disadvantages of each of

the techniques descri'ed.


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The Techniques

*an techniques have 'een develo"ed to ena'le'iological "schologists to understand ho+ the 'rain+or,s- each having their o+n advantages anddisadvantages.

t is rare that a single $ethod +ill "rovide aconvincing e/"lanation- $ore often one or $oretechniques are utilised to "rovide a clearer "icture.

This is referred to as 0converging o"erations0(1arlson- 3!.


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. 4euroanato$icalTechniques.

These tell us a'out the anato$ical structure of the 'rain.

a! 5istological 6rocedures: ross e/a$ination of the'rain does not allo+ us to stud details of cell structureand connectivit- to do so +e need to selectivel stainthin slices of the 'rain.

6reservation: %fter death the soft 'rain tissue isdestroed ' autoltic en8$es- so the 'rain $ust 'e"reserved +ith a 9/ative- such as for$alin.

The 'rain is then e$'edded +ithin a "aran 'loc, thatcan 'e sliced thinl using a $icroto$eand $ounted on

slides. 5istological stains have 'een develo"ed so that cell

'odies- nerve 9'res and $e$'ranes can 'e selectivelvie+ed


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2. $aging the Living Brain.

The $ethods "reviousl descri'ed have all requiredthe 'rain to 'e re$oved.

The follo+ing techniques ena'le neural structureand function to 'e vie+ed in the living 'rain.

1o$"uterised %/ial To$ogra"h(1%T!: 1onsists of acircular arrange$ent of /;ra e$itters and detectorsin +hich "rogressive scans through the 'rain can 'eta,en.

% 2;di$ensional i$age of hori8ontal sections can

then 'e "roduced. This technique is used $ainl to diagnose

neurological conditions such as tu$ours- 'lood clots-degenerative disease and the location of stro,es.


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1%T scan fro$ a "atient +ith alesion in the right occi"ital;"arietalarea.

Lesion site 1arlson (3! "


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*agnetic


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6ositron >$ission To$ogra"h(6>T!.


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6>T Scan of Brain

%ctivation.

4or$al elderl control %l8hei$er@s

"atient


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%dvantagesC)isadvantagesof Brain $aging.

%dvantages.

4on;invasive (1%T- *


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. lectrical %ctivitin the Brain.

%/ons generate action "otentials- and ter$inal'uttons elicit "ostsna"tic "otentials.

These electrical events can 'e recorded- andchanges in electrical activit can 'e used to

deter$ine +hether a structure or region of the 'rainis involved in a certain 'ehaviour.

There are t+o t"es of $easure:

a! *icroelectrodes: %re ver s$all and can recordelectrical activit +ithin single neurons (single;cell

recording!. These are nor$all i$"lanted chronicall into the

'rain of an ani$al thus allo+ing the $onitoring ofactivit as the ani$al res"onds to "articularenviron$ental sti$uli.


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%dvantagesC)isadvantagesof *icroelectrodes.

%dvantages.

>/tre$el "recise.

)isadvantages. Ti$e consu$ing.

Too focused ; it neglects neuronal interactions.

nvasive.


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'! *acroelectrodes.

The >lectroence"halogra$(>>! +as invented 'Berger(2!.

>lectrodes are attached to the scal" and the activitof hundreds of thousands of neurons in the vicinit

of the electrodes recorded. %ctiveelectrodes are "laced over the site of

e/"ected neural activit and an indi=erentelectrodeis "laced at a neutral s"ot (usuall the earlo'e!.

The recording si$"l $easures the "otential

di=erence 'et+een the t+o electrodes. n clinical studies- $an electrodes are used and

the are "laced over the lo'es of the 'rainaccording to a conventional sche$e.


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The >>


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%dvantagesC)isadvantagesof *acroelectrodes.

%dvantages.

4on;invasive

1an di=erentiate 'et+een di=erent neurological

conditions or 'ehavioural states.

)isadvantages.

Ti$e consu$ing.

er crude ; the averaging of activit in $an

neurons cannot esta'lish "recise activit in a"articular region.


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Functional near;infrared (f4

There are three t"es of f4


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)i=use o"tical i$aging ()#! or di=use o"ticalto$ogra"h ()#T! is a $edical i$aging Technique+hich uses near infrared light to generate i$ages ofthe 'rainC'od.

The technique $easures the o"tical a'sor"tion ofhe$oglo'in- and relies on the a'sor"tion s"ectru$ ofhe$oglo'in varing +ith its o/genation status.

5igh;densit di=use o"tical to$ogra"h (5);)#T! hasseen set'ac,s due to li$ited resolution.

5igh te$"oral resolution (H $s!

)i=use o"tical i$aging()#C)#T!


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#"tical coherence to$ogra"h (#1T! is an o"tical signalacquisition and "rocessing $ethod.

t ca"tures $icro$eter;resolution- three;di$ensionali$ages fro$ +ithin o"tical scattering $edia (e.g.-

'iological tissue!.

#"tical coherence to$ogra"h is an interfero$etrictechnique- t"icall e$"loing near;infrared light. Theuse of relativel long +avelength light allo+s it to"enetrate into the scattering $ediu$.

#"tical 1oherence To$ogra"h(#1T!


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3. Brain Sti$ulation.

n ani$als- direct electrical sti$ulation of the 'raincan "roduce clear 'ehavioural changes.

>.g sti$ulation of the h"othala$us $a "roducefeeding- drin,ing- se/ual arousal- and aggression

suggesting an activational role. Sti$ulation of the caudate nucleus often halts

ongoing 'ehaviour +hich suggests an inhi'itorrole.

n hu$ans this technique +as "ioneered ' 6en9eld

and Ias"er (A3! in +hich the sti$ulated variousregions of corte/ in conscious "atients and noted

do+n the 'ehavioural or sensor e=ects.


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>lectrical Sti$ulation ofthe 5u$an Brain

1arlson (3! "


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%dvantagesC)isadvantagesof Brain Sti$ulation.

%dvantages.

)oes not har$ the 'rain.

% valid +a of investigating living function of 'rain

areas.

)isadvantages.

nvasive.

1rude ; not eas to tell ho+ far the sti$ulation hass"read.


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1_brain imaging techniques

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