Task 8 - The lesioned brain Flashcards
Classical neuropsychology vs. Cognitive neuropsychology
Classical neuropsychology: Infering the function of a specific brain region by seeing what impairment people with lesions in that region have
Cognitive neuropsychology: Tries to infer the “building blocks” of cognition, irrespective of location
Single dissociation
Functional
Single dissociation: If patient is impaired at task A but relatively spared on task B. Differentiates between:
Classical single dissociation: Performs completely normal on task B
Strong single dissociation: Significantly more impaired on task A but impaired at both
Task-resource artifact and Task-demand artifact
Task-resource artifact: The use the same cognitive resource but task A just needs more of it
Task-demand artifact: Patient performs task A suboptimally (e.g. missed instructions, didn’t pay attention)
So basically you have to prove that dissociation is due to things really being independent or due to artifacts
Syndromes
A cluster of different symptoms that are believed to be related in some meaningful way
Single-case studies vs. group studies
In a single-case study you look at one person with a specific lesion, while in group studies you look for a group of people with similar lesions/impairments and average results
Three assumptions in cognitive neuropsychology
- The fractionation assumption
- The transparency assumption
- The universality assumption
The fractination assumption
Damage to the brain can produce selective cognitive lesions (refers to lesions within cognitive model, not the physical lesion itself)
The transparency assumption
Lesions affect one or more components within the preexisting cognitive system but do not result in a completely new cognitive system being created
The universality assumption
All cognitive systems are basically identical
Ways of grouping patients in lesion studies
- Grouping by syndrome: Assigned to a group on the basis of possessing a cluster of symptoms
- Grouping by cognitive symptom: On the basis of possessing one particular symptom
- Grouping by anatomical lesion
Double dissociation
Functional
Two single dissociations that have complementary profile, evidence for them being independent
Single and double dissociation
Localization
- Single dissociation: A lesion in region X produces an impairment of task A but not task B and a lesion in region Y produces impairment in neither
- Double dissociation: A lesion in region X produces impairment in task A, not B and lesion in region Y produces an impairment in task B
Diaschisis
Even a very discrete brain lesion can disrupt functioning of distant brain regions that are structurally intact
Hemineglect/hemi-inattention
Despite having intact sensory & motor function, people ignore, or don’t pay attention to, one side of space
Line bisection task
Often used to detect Hemineglect, where patient has to indicate the middle of a horizontal line
Localization vs. Necessity vs. Correlation
Lesion studies can provide evidence that a brain area is involved in a function (correlation), required for that function (necessity), or just localized to that function (but not necessarily the only part responsible)
Broca’s case
- Paul Broca studied a patient named “Tan”, who could understand language but had severe difficulty speaking, only able to say “tan.”
- After Tan’s death found lesion in the left inferior frontal gyrus (now called Broca’s area)
- Also implies seperate processes for speech production and speech comprehension
Limitations of Lesion Studies
- No two lesions are identical, making generalization difficult
- The brain may reorganize, masking true deficits
- Lesions may disrupt multiple functions, not just one
