Methods of Cognitive Neuroscience

1. Methods of Cognitive Neuroscience

13. Lesion Studies • Logic of Lesion Studies: • damaged area plays a role in accomplishing whatever task is deficient after the lesion

14. Lesion Studies • Types of Lesions • Animal • Human

16. Lesion Studies • Animal Lesion Techniques • Aspiration Lesions • Electrolytic Lesions

17. 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

18. Lesion Studies • Animal Lesion Techniques • Vascular Lesions • endothelin-1 • good model of human stroke • severe damage • not pinpoint accuracy

19. Lesion Studies • Animal Lesion Techniques • Reversible Lesions • cooling • Local anesthetic, other drugs • highly selective • can cool specific layers of cortex • can be reversed!

20. 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)

21. 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

22. 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

23. Lesion Studies • Human Lesions • Trauma • Frontal lobes are particularly susceptible • Some famous cases (e.g. Phineas Gage)

24. Lesion Studies • Human Lesions • Surgery • Often surgery done to treat epilepsy • Occasionally corpus callosum is severed • Problem: patient wasn’t “normal” before the surgery

25. 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

31. Lesion Studies • Making sense of Lesion studies

32. 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

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

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

35. Lesion Studies • Designing Lesion Studies • “design tasks that diagnose the function of specific operations” • First, use a control condition Lesion X Healthy Performance This difference indicates deficit A Task

36. Lesion Studies • Designing Lesion Studies • “design tasks that diagnose the function of specific operations” • But maybe this is a general deficit! - use 2nd task Lesion X Healthy Performance This difference indicates deficit A Task

37. Lesion Studies • Designing Lesion Studies • “design tasks that diagnose the function of specific operations” • But maybe this is a general deficit! - use 2nd task Lesion X Healthy Performance A B Task

38. Lesion Studies • Designing Lesion Studies • “design tasks that diagnose the function of specific operations” • But maybe this is a general deficit! - use 2nd task Lesion X Healthy Performance indicates that deficit is selective A B Task

39. Lesion Studies • Designing Lesion Studies • “design tasks that diagnose the function of specific operations” • This result is called a single dissociation Lesion X Healthy Performance indicates that deficit is selective A B Task

40. 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 Lesion X Healthy Performance Lesion Y A B Task

41. Lesion Studies • Designing Lesion Studies • “design tasks that diagnose the function of specific operations” • This result is a double dissociation Lesion X Healthy Performance Lesion Y Interaction suggests two lesions have specific and independent deficits A B Task