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