Methods of Cognitive Neuroscience

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Methods of Cognitive Neuroscience
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Lesion Studies

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

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Lesion Studies

• Types of Lesions
• Animal
• Human

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Lesion Studies

• Animal Lesion Techniques
• Aspiration Lesions
• Electrolytic Lesions

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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

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Lesion Studies

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

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Lesion Studies

• Animal Lesion Techniques
• Reversible Lesions
• cooling
• highly selective
• can cool specific layers of cortex
• can be reversed!

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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 Parkinsons 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)

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Lesion Studies

• Animal Lesion Techniques
• Gene Knock-Out
• can selectively block expression of specific
  receptor types
• animal developes differently

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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

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Lesion Studies

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

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Lesion Studies

• Human Lesions
• Surgery
• Often surgery done to treat epilepsy
• Occasionally corpus callosum is severed
• Problem patient wasnt normal before the
  surgery

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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

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Lesion Studies

• Making sense of Lesion studies

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Lesion Studies

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

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Lesion Studies

• Logic of Lesion Studies
• damaged area plays a role in accomplishing
  whatever task is deficient after the lesion
• Warning
• This isnt 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

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Lesion Studies

• Designing Lesion Studies
• design tasks that diagnose the function of
  specific operations
• First, use a control condition

Lesion X
Performance
A
Task
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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
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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
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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
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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
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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
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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
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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
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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