The Journal of Neuroscience, August 15, 1998, 18(16):6539-6548
Cerebrally Lateralized Mental Representations of Hand Shape
and Movement
Lawrence M.
Parsons1,
John D. E.
Gabrieli2,
Elizabeth A.
Phelps3, and
Michael S.
Gazzaniga4
1 Research Imaging Center, University of Texas Health
Science Center at San Antonio, San Antonio, Texas 78284, 2 Department of Psychology, Stanford University, Stanford,
California 94305, 3 Department of Psychology, Yale
University, New Haven, Connecticut 06520, and 4 Program in
Cognitive Neuroscience, Dartmouth College, Hanover, New Hampshire
03755
Previous psychophysical and neuroimaging studies suggest that
perceiving the handedness of a visually presented hand depends on
sensorimotor processes that are specific to the limb of the stimulus
and that may be controlled by the cerebral hemisphere contralateral to
the limb. Therefore, it was hypothesized that disconnection between
cerebral hemispheres would disrupt mental simulation of a hand
presented to the ipsilateral, but not the contralateral, hemisphere.
This hypothesis was examined by the present study in which two
callosotomy patients and eight healthy controls judged the handedness
of drawings of left and right hands in various positions, without
moving or inspecting their own hands. Stimuli were presented for 150 msec in the right or left visual hemifield. As predicted, for each
hemisphere, patients' accuracy was high when the hand was
contralateral to the perceiving hemisphere, but it was not above chance
when it was ipsilateral to the perceiving hemisphere. Controls'
accuracy was high in both conditions. Response time analyses indicate
patients, like controls, mentally simulated reaching into stimulus
postures. When the stimulus laterality was ipsilateral to the
perceiving hemisphere, patients imagined the hand contralateral to the
perceiving hemisphere reaching into the stimulus posture but did not
detect the mismatch, guessing with a response bias or responding on the
basis of shape similarity. We conclude that each hemisphere could
represent the shape and movement of the contralateral hand but could
not for the ipsilateral hand. Mentally simulating one's action and
discriminating body part handedness both depend on lateralized
sensorimotor and somatosensory representations.
Key words:
motor imagery; shape recognition; cerebral
lateralization; split brain; mental imagery; visual object
discrimination
Copyright © 1998 Society for Neuroscience 0270-6474/98/18166539-10$05.00/0
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