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