BIOLOGY 2C03 Lecture Notes - Premotor Cortex, Posterior Parietal Cortex, Unix System Iii

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28 Jan 2013
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Outline of Lecture 38 (03-06 A; Shadmehr)
Motor System III – Posterior Parietal Cortex
I. The posterior parietal cortex (PPC) determines eye-centered locations and plans movement
- The receptive field of visual cortex neurons (occipital lobe) is retinocentric
- PPC neurons receive eye/head position and image location information and encode them as the
gain of discharge rate and receptive field, respectively; this is all the information needed to for
PPC to compute target in eye-centered coordinates
- In a delay task, PPC neurons encode target of intended movement during delay period even if the
target disappears
- PPC does not encode forces needed to move to the target
- The PPC also computes hand position from visual and/or proprioception input; the visual sight
of one’s own hand is particularly meaningful, as there are PPC cells that only respond to the image
of the hand in certain positions
- Premotor cortex subtracts hand position from target position to determine displacement vector
for hand and decides whether or not to execute the movement
II. Effects of a lesion of the PPC
- Lesion of the PPC does not affect the ability to sense the environment, but does cause neglect of
the contralateral space (unable plan actions on objects on opposite side of body)
- Recall that individual functions in the brain are segregated, so the above should not be surprising
- Rehabilitation of PPC lesion patients can be done with prism glasses, which can have a long-
term effect
Summary of major points
- Understand what types of information the PPC processes
- Understand what the PPC does and does not do with respect to motor control
- Understand the relationship between the PPC and primary motor cortex
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