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Abstract:
Lesions of the corpus callosum (CC) can result in apraxia of
the left limbs. It is controversial whether left-sided apraxia is
confined to movements on verbal commands or affects imitation as
well. Defective imitation was described in patients with lesions of
the CC following bleeding or infarction. By contrast, Gazzaniga et
al. (1967) reported faultless imitation of finger postures with the
contralateral hand by both hemispheres of patients after surgical
section of the CC. We report a patient in whom the posterior and
middle portion of the CC have been severed by embolization and
operation of an arteriovenous malformation. Pictures of meaningless
gestures were tachistocopically presented to the left or right
visual hemifield and the patient was asked to imitate them with the
left or right hand. There were 10 finger postures and 10 postures
varying the position of the whole hand relative to the face and
head. Each combination of gesture, hemifield, and hand was tested.
Performance with the ipsilateral hand was defective for both
hemispheres and both kinds of gestures, and contralateral finger
postures were defective for both hemispheres. By contrast,
contralateral imitation of hand postures was nearly perfect for the
left hemisphere and severely defective for the right. A similar
result was obtained with matching of unilaterally presented
gestures to a multiple choice array presented in free vision.
Whereas matching of finger positions was mildly defective with
either hemisphere, matching of hand postures was virtually perfect
with the left hemisphere and near chance with the right. We will
discuss the relevance of these findings for cognitive models of
imitation of gestures.
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