APRAXIA DURING WADA TESTING

Apraxia is the loss of the ability to perform learned skilled movement s correctly. In right-handers, apraxia and aphasia are most frequently associated with left-hemisphere lesions. When they are dissociated, h owever, aphasia is more common in the absence of apraxia than vice ver sa. There are two hypotheses that can account for this discrepancy: (1 ) in right-handers, praxis is more likely than language to be mediated by the right hemisphere, or (2) the left-hemisphere network that medi ates language is either more widely distributed than the network that mediates praxis or is more likely to be in the middle cerebral artery distribution. We studied apraxia in a group of right-handers undergoin g selective hemispheric anesthesia, or Wada testing. All nine subjects had language lateralized to the left hemisphere, and seven of the nin e had praxis lateralized to the left hemisphere. Two of the subjects h ad praxis bilaterally represented. Although our data suggest that spee ch and praxis functions tend to be lateralized to the left hemisphere in most right-handers, praxis appears to be more distributed between t he hemispheres than speech-language functions. Furthermore, an analysi s of the types of errors made during praxis testing suggests different ial roles of the hemispheres in praxis functions.