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Abstract:
Sensory representations of arm and hand in the postcentral gyrus are usually supposed to be strictly lateralized and to allow a spatially unbiased representation of the position of the contralateral limb in egocentric space. Here we report a patient whose behavior suggests a different
organization of proprioceptive representations. Patient R.W. demonstrated an isolated proprioceptive deficit without hemiparesis due to a lesion of the right postcentral gyrus. We examined her limb position sense in a finger position matching task. Target locations were
defined by passively positioning the index finger of one hand beneath a table surface. With the other hand above the table R.W. indicated the perceived position of the finger below the table. Without visual feedback of either hand, we observed a significant leftward shift of perceived locations when reaching with the right hand and an opposite rightward shift when reaching with the left hand in comparison to age-matched healthy controls. These directional errors improved when vision of the active hand was allowed. However, position errors were still significantly different from the control group even with free view of the contralesional hand. Pointing to visual targets without feedback of the moving hand, R.W. revealed errors with both hands that were significantly different from the performance of healthy controls. However, pointing to visual targets with full visual feedback, R.W. was as accurate as controls with either hand. Thus we can exclude a contribution of subclinical visual or motor deficits to the observed impairments. In summary, our data show a contralesional shift of the perceived position of the contralesional hand suggesting a directional bias of proprioceptive representations. Furthermore, our data reveals an effect of the right hemisphere lesion on
proprioceptive information processing for the ipsilateral hand.
