NROC64: Reaching and Grasping Article

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30 Mar 2012
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Intro:
Prehension mvts w/ visual guidance = ctrl by 2 parallel visuomotor channels
oOne channel = reaching; other channel = grasping
Reaching:
oMedial parietofrontal circuit
Superior parietal lobule (SPL)
Dorsal premotor cortex (PMd)
Grasping:
oLateral parietofrontal circuit
Inferior parietal lobule (IPL)
Ventral premotor cortex (PMv)
But not exactly dichotomized;
oPathways that link post. parietal cortex to PMd & PMv = partial overlap
oPMd & PMv contain cells encoding arm direction of mvt & proximal /
distal representations of the arm
oBoth circuits probably involved in both reaching and grasping
Reaching:
Complex spatial problem, involves reference sys for to code:
oPosition of reaching hand
oPosition of to-be-reached object
Limb starting position + eye position + target location integration by
oFrontal and parietal cortex circuit:
Motor areas
Regions of frontal lobe
Posterior parietal regions = space perception, action guidance =
SENSORY CTRL OF ACTION anatomical position = btn visual
cortex & somatosensory cortex
Reaching in Monkey:
oFrontoparietal reach-related neurons integrate spatial variables:
Spatial location
Distance
Physical dimension
oPost parietal has neurons that respond during execution of reaching mvts
Visual area (V6A) = in superior parietal lobe; active when monkey
asked to push/pull lever outside field of view
Activated by eye-position signals
oFrontal (PMd & PMv) influenced by eye-position signals
Target localization transformation from visuospatial to motor
coordinates for reaching
oCoding visually guided reaching = needs integration of multisensory info
into comparable frames of reference = relies on combinatorial properties of
frontal & parietal reach neurons
oEarly formation of motor commands for reaching in parietal cortex
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