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The Journal of Neuroscience, November 1, 1998, 18(21):9038-9054
Partial Inactivation of the Primary Motor Cortex Hand Area:
Effects on Individuated Finger Movements
Marc H.
Schieber1, 2, 3, 4 and
Andrew V.
Poliakov1
Departments of 1 Neurology and
2 Neurobiology and Anatomy, Brain and Cognitive Science,
and Physical Medicine and Rehabilitation, 3 Center for
Visual Science, and 4 Brain Injury Rehabilitation Program
at St. Mary's Hospital, University of Rochester School of Medicine and
Dentistry, Rochester, New York 14642
After large lesions of the primary motor cortex (M1), voluntary
movements of affected body parts are weak and slow. In addition, the
relative independence of moving one body part without others is lost;
attempts at individuated movements of a given body part are accompanied
by excessive, unintended motion of contiguous body parts. The effects
of partial inactivation of the M1 hand area are comparatively unknown,
however. If the M1 hand area contains the somatotopically ordered
finger representations implied by the classic homunculus or
simiusculus, then partial inactivation might produce weakness,
slowness, and loss of independence of one or two adjacent digits
without affecting other digits. But if control of each finger movement
is distributed in the M1 hand area as many studies suggest, then
partial inactivation might produce dissociation of weakness, slowness,
and relative independence of movement, and which fingers movements are
impaired might be unrelated to the location of the inactivation along
the central sulcus.
To investigate the motoric deficits resulting from partial inactivation
of the M1 hand area, we therefore made single intracortical injections
of muscimol as trained monkeys performed visually cued, individuated
flexion-extension movements of the fingers and wrist. We found little
if any evidence that which finger movements were impaired after each
injection was related to the injection location along the central
sulcus. Unimpaired fingers could be flanked on both sides by impaired
fingers, and the flexion movements of a given finger could be
unaffected even though the extension movements were impaired, or vice
versa. Partial inactivation also could produce dissociated weakness and
slowness versus loss of independence in a given finger movement. These
findings suggest that control of each individuated finger movement is
distributed widely in the M1 hand area.
Key words:
cortex; dexterity; finger; individuation; macaque; motor; muscimol; response time, somatotopy; weakness
Copyright © 1998 Society for Neuroscience 0270-6474/98/18219038-17$05.00/0
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