Lesions Flashcards
- Localization of function, lesion method:
principle, assumptions, limitations, and dis-
/advantages (compared with fMRI)
Investigation of the effect of damage to a particular area Classical neuropsychology
● Infers the function of a given brain region by taking patients with lesions to that region and examining their pattern of impaired/ spared abilities
● Brain based
● Important source of constraints for functional imaging data
● Favours group studies: more appropriate for establishing lesion-deficit associations
Cognitive neuropsychology
● Patterns of impaired/ spared abilities used to infer the building blocks of cognition
(irrespective of location)
● Important for development of detailed information processing models
● Provides framework that underpins imaging research
● Favours single-case studies (more appropriate for establishing how cognitive processes are
subdivided)
- Single and double dissociations (with or
without anatomical information about the
lesion)
Dissociation of function: performance on one task is impaired, whereas performance on another isn’t. Functions and processes are dissociable and separable.
● Logic: separate neural resources may be indicated by difficulty in one domain relative to absence of difficulty in another domain
o Not necessarily linked to different locations
o Cannot conclude that it is the only function of the neurons ● Requires range of relevant tasks to interpret performance
Single Dissociation:
Non-reciprocal dissociation of function
o Impairment may be present on task A but relatively not on task B
● Interpretations:
o Hierarchical relationship: 2 functions are separate to some degree, but one is
necessary for the other
o Task-resource artifact: tasks A and B may use same resource but one requires it more
than the other. If this resource is subsequently damaged or impaired, the task requiring
it more will suffer more
o Task-demand artifact: single dissociation occurs because patient performs
sub-optimally on one task, not strictly due to impairment, but rather because
impairment has made the task difficult to understand
Double Dissociation:
● Reciprocal dissociation of function
o Impairment is on opposite tasks
● Each lesion-impairment serves as control for the other
● Interpretations
o Provides evidence that 2 functions are relatively independent
o With each lesion, we learn about the involvement in one function but not the other ● Localisation
o Firmer grounds for localisation: lesion in region X versus region Y
Association:
Association
● Consistent co-occurrence of 2+ impairments. Suggests one underlying process, perhaps due to proximity
● Localisation
o Suggests a single region is necessary for different functions
o Functions may be separable but mediating brain areas are in close proximity, and
therefore impairment co-occurs
- Single-case vs group studies: principles,
relative dis-/advantages
Advantages of Single Case Studies:
Why choose single case?
o Averaging lesioned groups is complicated because differences may be attributed to
differences in lesions rather than just noise
o Determining where the lesion is cognitively can only occur through empirical
examination of each case
o A group of identical patients is still basically a single case study
o Does provide valid data, with which scientists can test, adapt and develop cognitive
theories.
Group Studies:
● Important for establishing whether regions are critical for performing given tasks ● Grouping
o By syndrome (cluster of symptoms): coarse level of analysis, more appropriate for understanding neural correlates of a given disease pathology rather than developing theories concerning neural basis cognition.
o By cognitive symptom (one in particular): finer analysis, made possible by techniques that compare lesion locations from MRI voxel-by-voxel. More likely to find hotspot. Can reveal more than one region as being critically involved.
o By anatomical lesion: when there is a specific testable prediction about what the region is critical for.
- Interpretation of data from lesion method
or fMRI: localization vs necessity vs
correlation
Limitations to the Interpretation
Localisation problems
● Assumes modularity/ localisation: discrete, anatomical modules dealing with different
cognitive functions (not the case, more distributed)
● Dissociation doesn’t mean that important function is vocalised in lesion area, only that the
area is necessary. Other regions may still be involved
● Diaschisis: lesion may cause long-term disruptive effects in distant regions although they still
function normally Lesion localisation
● Structural imaging techniques are suboptimal at identifying lesions. Cannot pinpoint exact location, and may be temporary disruptions due to surrounding area (swelling, bleeding, etc.)
● Reliable lesion images best obtained 3 months after onset Differential vulnerability
● Some areas of the brain are more likely to be disrupted by stokes: not randomly distributed. Therefore, makes it difficult to interpret lesion overlay plots – possible that the regions are not specifically involved, but rather just commonly damaged.
Temporal resolution
● Lesion method doesn’t allow for assessment of time course of information processing
● Necessary for determining stages of processing and role of feedback
- Exemplary applications of the lesion
method: Broca’s case, spatial neglect, vision
vs visual imagery
to be done
