Unilateral hemispheric stroke disrupts the inter-hemispheric balance which is normally maintained by reciprocal inhibitory influences exerted by each hemisphere on the other. This leads to a state where the damaged hemisphere loses its capacity to support function, beyond the direct outcome of focal tissue loss, due to widespread physiological suppression by the overactive healthy hemisphere. This line of theorizing dominates the practice of tDCS and rTMS application in stroke rehabilitation, where reversal of the pathological balance is aimed using excitatory stimulation of the damaged hemisphere and/or inhibitory stimulation of the healthy hemisphere. We present here an examination of the ‘reciprocal inhibition’ concept in a patient with callosal section.

GH (M/35) suffered from idiopathic epilepsy with major convulsions almost every day, despite intensive efforts to control disease activity pharmacologically. He was admitted for rehabilitation after a complete surgical section of the forebrain commissures, leaving him with marked apraxia and tactile anomia in the left hand, and with manifestations resembling left neglect dyslexia. Given the disconnection of each hemisphere from the other, performance of diagnostic tests for spatial neglect, by each hand, is assumed to reflect the net effect of the contralateral hemisphere, in the absence of inhibitory influences exerted by the ipsilateral hemisphere.

In representational-drawing and figure-copying tasks executed by the dominant right-hand, GH manifested classical left-side neglect. Each of the two disconnected hemispheres demonstrated ipsilateral inattention in manual cancellation and line bisection tasks. Displacement of the subjective midpoint in line bisection performance was greater in right-hand (left-hemisphere) performance.

As the postoperative MRI disclosed no extra-callosal damage, the left neglect pattern shown by the isolated left-hemisphere (right-hand) points to an important role of “completion” rather than “rivalry” in inter-hemispheric relationships, raising questions with regard to current practices of non-invasive brain stimulation in stroke rehabilitation.