Assessment, Localisation & Theory


What is the history of localisation of function?

Gall (18thC) first proposed that the cortex was the functioning part of the brain. They used dissection to demonstrate the existance of the corticospinal pathway. They also recognised the role of the corpus callosum. 

Flourens (19thC) used lab experiments to remove different parts of the cortex in animals to observe behaviour. Found evidence against localisation, but was criticised for not testing hypotheses sufficiently.

Bouillard (19thC) argued that speech is in the FLs and language is in the left hemi. Broca (19thC) had a patient who could only say "tan." An autopsy showed a left FL lesion, and this was known as expressive dysphasia.

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What is the Wernicke-Geschwind model?

The idea that disconnection from Wernicke's area (first temporal gyrus) from Broca's area would leave comprehension and spontaneous speech intact, but leave someone unable to repeat speech. This is conduction aphasia.

Speech production is not affected when Broca's area is intact, and comprehension is not affected when Wernicke's area is intact.

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What are some research approaches in NP?

How good is a test at detecting brain damage? This involves comparing patients with brain damage to healthy controls.

How good is a test at distinguishing lesion location? This compares patients with a lesion in one area with patients with a lesion in another. There is control of general loss of function due to brain injury.

Functional imaging looks at neural correlates of cognitive tasks in healthy individuals, whereas neuropsychology looks at deficits in cognitive testing in impaired individuals. This provides information about what is necessary, rather than what is sufficient.

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What can occur with a left hemi lesion?

Left hemi is dominant for language and is independent of hearing, meaning a deaf-person can lose the ability to sign if the left hemi is damaged.

Left hemi disorders include problems in (Lezak, 2005): verbal memory, verbal fluency, abstract thinking, reading, writing, and arithmetic. They may also have problems with loss of constructional abilities, difficulty with complex motor sequences, and difficulties with object recognition.

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What can occur with a right hemi lesion?

Signs of right hemi lesions may include problems with verbal fluency, ordering, organising, making sense of complex stimuli, maintaining alterness and arousal.

There may also be perceptual difficulties, difficulties with spatial orientation and visuo-sparial memory, problems with constructional tasks and difficulty with visual memory.

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What is object agnosia?

Apperceptive agnosia is where they can see an object but not synthesize the elements of what they see. This is often associated with occipital lobe lesions (Vuilleumier, 2001).

Associative agnosia is where they can perceive the object but not work out what it is. It is often associated with left occipto-temporal lobe lesion (Di Renzi, 2000).

Prosopagnosia is associated with right occipito-temporal lesions.

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What are the differences between dorsal & ventral

Dorsal system runs from the OL to the PL and is involved in spatial recognition (where?). It can result in a patient getting lost due to spatial disorientation and is assessed with spatial tasks.

Ventral system runs from the OL to the TL and is involves in object recognition (what?). Patients can get lost due to inability to recognise landmarks and is assessed with object recognition tasks.

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What do the parietal lobes do?

Functions as the association cortex.

Deficits in the PL include: constructional deficits, slowed ability to disengage attention, STM disorders, disruption of temporal order, and tactile agnosia if damage is to somatosensory areas representing the hands.

Deficits in the left hemi of the PL include: fluent aphasia, impaired recognition of semantics, reading and writing problems, apraxia (ability to produce motor actions), acalculia and agraphia.

Deficits in the right hemi of the PL include: sensory neglect, apraxia for dressing, anosagnosia and impaired spatial thought.

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What do the temporal lobes do?

Houses the auditory cortex and deficits are associated with hearing. Deficits may also include problems with memory and learning of new information (limbic system), LT storage and semantic memory (superior temporal gyri).

Left hemi TL deficits include difficulties with language comprehension.

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What do the frontal lobes do?

Deficits in the FLs include integration of motor skills and learned action sequences (premotor division), and integrating behaviour components at the highest level (PFC). It is also associated with exec function.

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What is the role of the FL in memory?

Functional neuroimaging data shows that the right PFC and anterior temporal cortex are necessary for retrieval of old info (Fink, 1996).

Poor recall with preserved recognition may reflect executive deficits.

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What are the different types of exec func tests?

Generativity - verbal fluency and design fluency

Planning - tower test, zoo map, key search

Inhibition - stroop, hayling

Mental flexibility - trails, brixton, rule shift, WCST

Judgement - cognitive estimates, 20 Qs, temporal judgement

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How good are cognitive tests at localisation?

Milner (1963) used the WCST to find differences between patients with dorsolateral lesions and those with orbitofrontal/ posterior lesions.

Damakis (2003) compared frontal lesion patients with those with posterior lesions, and found frontal patients performed more poorly.

However, Anderson (1991) found normal performance in individuals with significant frontal pathology.

Burgess et al. (1997) found patients with frontal lesions slower at Hayling, and those with anterior lesions made more errors than those with posterior lesions on the Brixton.

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What factors limit a tests ability to localise les

Sensitivity (how good a test is at picking something up) and specificity (how good a test is at not picking something else up by mistake).

The standard form of lateralisation applies most strongly to right-handed males, but even then atypical lateralisation can occur.

Diffuse brain damage does not affect all systems equally, and it is rare to find focal injury without any diffuse effects. Diffuse damage can occur in closed head injury, infection, and degenerative conditions, whereas focal lesions are more likely to occur with tumours and stroke. 

Cognitive abilities are likely distributed throughout the brain, so although certain regions are critical for certain functions, they do not work in isolation. Lesions in different locations may produce similar effects due to effect on a singular pathway.

Location is often more important than size in stroke patients (Powers, 1990), whereas size is more important in TBI as the damage is generally more widespread. Therefore, size vs location depends on the type of pathology.

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How can accuracy of interpretation be improved?

Tests should not be interpreted in isolation, they require a full assessment. Scans should also be used (if available) to back up the data.

Detailed history may provide more information about diffuse vs focal damage, and long term history may be useful for identifying other risk factors.

The more rapid the onset of symptoms, the more likely factors such as diaschisis are likely to be relevant, and you need to make sure reversible medical conditions are excluded. Other neurological factors such as sensory and motor problems should be considered.

Note if someone is left-handed.

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