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 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 can selectively block expression of specific receptor types animal developes differently

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 Why are there only certain kinds of deficits associated with lesions? Why not every possible deficit?

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 Task A Lesion X

Lesion Studies Designing Lesion Studies –“design tasks that diagnose the function of specific operations” –First, use a control condition Performance Task A Lesion X Healthy

Lesion Studies Designing Lesion Studies –“design tasks that diagnose the function of specific operations” –First, use a control condition Performance Task A Lesion X Healthy This 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 Task A Lesion X Healthy This 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 Task A 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 Task A 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 Task A 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 Task A 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 Task A Lesion X Healthy B Lesion Y Interaction suggests two lesions have specific and independent deficits