methods of cognitive neuroscience. lesion studies logic of lesion studies: –damaged area plays a...
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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
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