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8 Apraxia, So monkeys told to point at landmark (where pathway), monkeys…
8 Apraxia
NEUROANATOMY OF APRAXIA
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Where vs. What pathway
Study on monkeys
So this is about two general pathways in the brain for visual recognition - single cell recordings on monkeys doing landmark task showed that "what" pathway is at the ventral stream, and "where" pathway is dorsal stream.
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Neuroimaging evidence
Patient with limb apraxia had left ventral premotor area and left posterior parietal area activate only when observing tools.
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LIMB APRAXIA
DEFINITION
The patient has a deficit in performing skilled, purposeful movement, but it isn't due to a motor deficit or a cognitive impairment. Patients usually have left hemisphere damage, and this area controls both limbs, hence if this area is damaged then both limbs are impaired.
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IDEOMOTOR LIMB APRAXIA
So here the patient understands the function of an object, but they have a deficit in manipulating the object/executing movement - Here they have a manipulation problem; so they have problems with the movement and timing of movement e.g. carve a turkey horizontally and poorly timed. they also have hand position errors, where they position their hands incorrectly when doing things such as grasping a toothbrush. They commonly have damage to left hemisphere
IDEATIONAL APRAXIA
The patient here does not know the function of an object e.g. if you ask them to point to the object that cuts, they cannot do that. Here they have a conceptual problem where they don't have the knowledge about object function. (but they have intact movement)
APRAXIA
TWO TYPES OF APRAXIA
Apraxia is a movement disorder, and apraxia can either be dyspraxia (developmental apraxia - coordination difficulty) or it can be acquired apraxia (motor coordination, dementia or stroke)
EVERY DAY FUNCTIONING
Patients with apraxia are more likely to not recover that well compared to other deficits. They are unable to return to work, and they cannot perform daily activities such as making a cup of tea, poorer eating habits, poorer everyday functioning.
SUB-TYPES OF APRAXIA
Bc of lack of research, there isn't firm understanding of the condition. But there is buccofocal, motor aphasia, ideomotor apraxia, ideational apraxia.
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So monkeys told to point at landmark (where pathway), monkeys told to look at a particular landmark (what pathway), and DF acc made movement to insert the slot (how pathway - i.e. how to do this movement).
Then mirror neurons are found to be involved in this how pathway, because they activate when we do movement (thus they may have motor programmes).
And this triangulation of evidence shows that left ventral premotor and left posterior parietal areas are involved in this "how" pathway of how to move and make movement (which is now suggested to be damaged in apraxia patients).
Hellman's model actually shows us how this "how" pathway may go in the left parietal lobes.