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 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, compare lesion to healthy control Performance Task A Lesion X Healthy This difference indicates deficit better worse

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

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

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

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

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 Task A Lesion X Healthy B Lesion Y Performance better worse

Lesion Studies Designing Lesion Studies –“design tasks that diagnose the function of specific operations” –This result is a double dissociation – suggests functional independence of distinct regions or processes Task A Lesion X B Lesion Y Performance better worse

Comparing Imaging Techniques - Advantages fMRI –ubiquitous –high spatial resolution –non-invasive/safe PET –quiet –labels variety of molecules EEG/ERP –inexpensive –high temporal resolution –non-invasive/safe MEG –high-temporal resolution –good but limited spatial resolution –non-invasive/safe Unit Recording –very high spatial resolution –high temporal resolution Lesions –real-life

Comparing Imaging Techniques - Disadvantages fMRI –loud –expensive –limited temporal resolution PET –very expensive –limited safety –invasive –limited temporal resolution EEG/ERP –limited spatial resolution –can be difficult to interpret MEG –limited spatial resolution –difficult to interpret Unit Recording –very invasive –can be hard to see “big picture” Lesions –very invasive

Temporal and Spatial Resolution are Traded Off

Cognitive Psychology High resolution instrumentation is of no use if you don’t understand the cognitive operations that you are trying to image Cognitive psychologists have worked to understand mental operations for over a century The enterprise of Cognitive Neuroscience is predicated on cognitive psychology

Cognitive Operations What does the brain actually do?