PS263 Chapter Notes -Posterior Parietal Cortex, Postcentral Gyrus, Frontal Lobe

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Published on 12 Apr 2013
PS263 Chapter 8 The Sensorimotor System
Three Principles of Sensorimotor Function
1. Hierarchical Organization: Sensorimotor is directed by commands that
cascade down through the levels of a hierarchy from the association
(highest) to the muscles (lowest) Information flows down
a. Advantage: Higher levels of the hierarchy are left free to perform
more complex functions (parallel signals flow between & over
multiple paths)
b. Functional Segregation: Each level of the system & company
hierarchies tends to be composed of different units, each of which
performs a different function.
2. Motor Output guided by Sensory Input: Eyes, organs of balance, and
receptors in skin monitor body’s responses & feed their information back
into the sensorimotor circuit.
a. Sensory Feedback plays an important role in directing the
continuation of the responses that produced it.
b. Ballistic Responses: not normally influenced by sensory feedback
brief, all-or-none, high-speed movements (I.e., swatting a fly)
3. Learning Changes the Nature & Locus: During the initial stages of motor
learning, each response is performed under conscious control after much
practice the indicidual responses become organized into continuous
integrated sequences of action that flow smoothly & are adjusted by sensory
feedback without conscious regulation.
Sensorimotor Association Cortex
At the top of the sensorimotor hierarchy, divided into two major areas:
1. Posterior Parietal Association Cortex: Posterior to the primary
somatosensory cortex, important role in integrating: directing behaviour by
providing spatial information and in directing attention; receives substantial
information, input from more than one system but from 3 systems (visual,
audio & somatosensory)
a. Output goes to areas of the motor cortex in the frontal cortex
(dorsolateral prefrontal association cortex to secondary motor cortex
and frontal eye field: small area of prefrontal, controls eye movement)
b. Damage deficits in perception & memory of special relationships,
accurate reaching and grasping, controlling eye movement & attention
c. Apraxia: Disorder of voluntary movement that is not attributable to a
simple motor deficit or to any deficit in comprehension or motivation.
d. Contralateral Neglect: Disturbance of a patients ability to response to
stimuli on the side of the body opposite to the brain lesion in the
absence of simple sensory or motor deficits left side of world gone:
i. Egocentric Left: when patients tilt their heads, their field of
neglect is not normally tilted with it - Lesions on the right
posterior parietal lobe
2. Dorsolateral Prefrontal Association Cortex: Receives projections from the
posterior parietal cortex and sends them to areas of the secondary & primary
motor cortex as well as the frontal eye field. Plays a role in the evaluation of
external stimuli & initiation of voluntary reactions to them.
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