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Summary 8. Task - Brain damage
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Summary of Task 8 of Methods of Cognitive Neuroscience
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TASK 8: BRAIN DAMAGELOCALISATION OF FUNCTION & LESION METHOD
Reverse engineering – attempt to infer function of a component by observing what the
rest of the cognitive system can & can’t do when that component / region is removed
Locate lesion through brain imaging
Assess neuropsychological deficits through testing
Infer specific impairments in behaviour / cognition
Insights into the original function of the injured brain
Basic strategy – investigate the effect of damage to a particular area
Lower animals – localised lesions explicit testing of hypotheses
Humans – effect of lesions that have already occurred through disease / trauma
Advantage: can assess functions that are specifically human / more developed
in humans
Limitations
Modularity / localisation assumption – assume discrete anatomical modules deal with
different cognitive functions
Problem of modularity – most brain damage is not limited by the boundaries of the
underlying functional modules
Plasticity makes it difficult to infer original function of healthy brain also makes
comparisons between subjects difficult
Test in acute stage of illness – won’t be able to accurately identify all impaired
brain regions
Wait for initial problems to resolve – problems associated with brain plasticity
will become more pronounced
Differential vulnerability – some areas of the cortex are particularly likely to be
damaged
Brain regions can be disabled but intact after injury
Poor temporal resolution – does not allow us to assess time course of information
processing, most injuries are permanent
Lesion is not an independent variable, because you can’t control it (it depends on
external causes)
Generalisation not possible – one person not enough to generalise, difficult to find a lot
of lesion patients with same lesion in the same area
Lesion subtraction – control patients indispensable for valid anatomical conclusions – just
because damaged regions are the same, does not mean they are directly involved in
disorder, they might just be vulnerable to injury
Must have brain lesions in same hemisphere & must be similar to patients
Regions of the brain simply vulnerable to brain damage should be commonly damaged in
both groups
, Regions involved in specific function, selectively damaged in those patients who have
problems there
ANIMAL MODELS IN NEUROPSYCHOLOGY
Behavioural neuroscience – humans think but animals behave OR we can’t be sure that
animals think
Far more selective lesions can be carried out in animals than humans
Each animal can serve as its own control by comparing performance before & after
the lesion
Common to have control groups that have undergone surgery but received no
lesion
Different lesioning methods
Aspiration – region is suctioned out, strong current seals the wound
Transection – cutting of discrete white matter bundles
Neurochemical lesions – toxins create chemical reactions that kill cells
Reversible “lesion” – pharmacological manipulations
Enabled more detailed anatomical understanding of the brain & anatomical
connectivity between regions
Limitations: (1) welfare of the animals, (2) some human traits don’t have obvious
counterparts in other species, e.g., language
LESION STUDIES VS. MODERN IMAGING TECHNIQUES
Lesion studies Modern imaging techniques
Fills unique niche to
understand the intact Enable us to identify damaged brain regions in vivo
brain Can eliminate problems of differential vulnerability,
Necessary to identify plasticity & disconnection associated with lesion
location & extent of a method + better temporal resolution
brain injury Interpretation can be difficult & has clear limitations
Limitations: modularity, Don’t know whether a region is necessary to
differential vulnerability, perform a task
plasticity, disconnection Can’t detect possible contributions of regions that
associated with lesion are constantly active
methods, poor temporal Not as accurate in stroke patients, because there’s
resolution less blood flow in the area where the stroke was
Measure disruption NOT BUT that doesn’t mean that area isn’t active
activation here we can Much more sensitive in young than old ppl
infer necessity Not sensitive for elderly stroke patients
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