Methods of Cognitive Neuroscience

Lesion Studies

• Logic of Lesion Studies:– damaged area plays a role in accomplishing whatever task

is deficient after the lesion

Lesion Studies

• Types of Lesions– Animal– Human

Lesion Studies

• Animal Lesion Techniques– Aspiration Lesions– Electrolytic Lesions

Lesion Studies

• Animal Lesion Techniques– Aspiration Lesions– Electrolytic Lesions

– Problems:• These can damage surrounding tissue - especially white matter

tracts nearby (“fibers of passage”)

• Irreversible

• eventual degradation of connected areas

Lesion Studies

• Animal Lesion Techniques– Vascular Lesions

• endothelin-1• good model of human stroke• severe damage• not pinpoint accuracy

Lesion Studies

• Animal Lesion Techniques– Reversible Lesions

• cooling• Local anesthetic, other drugs• highly selective• can cool specific layers of cortex• can be reversed!

Lesion Studies

• Animal Lesion Techniques– Selective Pharmacological lesions

• damage or destroy entire pathways that have a specific sensitivity to a particular chemical

• e.g. MPTP model of Parkinson’s Disease (frozen addicts)• e.g. scapolomine - acetylcholine antagonist - temporary

amnesia

• Can be selective for specific circuits but not for specific brain areas

• can be reversible in some cases (e.g. scopolamine, but not MPTP)

Lesion Studies

• Animal Lesion Techniques– Gene Knock-Out/Knock-In (Transgenics)

• can selectively block/enhance expression• Viral vectors, electroporation• animal develops differently

• Can have temporal/regional/molecular specificity

Lesion Studies

• Human Lesions– Ischemic Events

• Stroke and Hemorrhage:– typically due to blood clot or hemorrhage– size of lesion depends on where clot gets lodged– amount of damage depends on how long clot remains lodged

Lesion Studies

• Human Lesions– Trauma

• Frontal lobes are particularly susceptible• Some famous cases (e.g. Phineas Gage)

Lesion Studies

• Human Lesions– Surgery

• Often surgery done to treat epilepsy• Occasionally corpus callosum is severed

• Problem: patient wasn’t “normal” before the surgery

Lesion Studies

• Human Lesions– Transcranial Magnetic Stimulation

• Electromagnet Induces current in the brain• very transient, very focal reversible “lesion”

• Believed to be safe• sites that can be studied are limited by the geometry of the

head

Lesion Studies

• Making sense of Lesion studies

Lesion Studies

• Logic of Lesion Studies:– damaged area plays a role in accomplishing whatever task

is deficient after the lesion

• Warning:– This isn’t the same as saying the lesioned area “does” the

operation in question– examples:

• normal behaviour may be altered to accommodate lesion– e.g. sensory loss of one arm favors other arm

• lesion might cause “upstream problem” or general deficit– e.g. attention problem “looks like” specific deficit if you only test

one specific demanding task

Lesion Studies

• Designing Lesion Studies– “design tasks that diagnose the function of specific

operations”

– First, use a control condition

Performance

TaskA

Lesion X

Lesion Studies

• Designing Lesion Studies– “design tasks that diagnose the function of specific

operations”

– First, use a control condition

Performance

TaskA

Lesion X

Healthy

Lesion Studies

• Designing Lesion Studies– “design tasks that diagnose the function of specific

operations”

– First, use a control condition

Performance

TaskA

Lesion X

HealthyThis difference indicates deficit

Lesion Studies

• Designing Lesion Studies– “design tasks that diagnose the function of specific

operations”

– But maybe this is a general deficit! - use 2nd task

Performance

TaskA

Lesion X

HealthyThis difference indicates deficit

Lesion Studies

• Designing Lesion Studies– “design tasks that diagnose the function of specific

operations”

– But maybe this is a general deficit! - use 2nd task

Performance

TaskA

Lesion X

Healthy

B

Lesion Studies

• Designing Lesion Studies– “design tasks that diagnose the function of specific

operations”

– But maybe this is a general deficit! - use 2nd task

Performance

TaskA

Lesion X

Healthy

B

indicates that deficit is selective

Lesion Studies

• Designing Lesion Studies– “design tasks that diagnose the function of specific

operations”

– This result is called a single dissociation

Performance

TaskA

Lesion X

Healthy

B

indicates that deficit is selective

Lesion Studies

• Designing Lesion Studies– “design tasks that diagnose the function of specific

operations”

– What if Task A is just harder than B? - add a 2nd group

Performance

TaskA

Lesion X

Healthy

B

Lesion Y

Lesion Studies

• Designing Lesion Studies– “design tasks that diagnose the function of specific

operations”

– This result is a double dissociation

Performance

TaskA

Lesion X

Healthy

B

Lesion Y

Interaction suggests two lesions have specific and independent deficits