Active tool use with the contralesional hand can reduce cross-modal extinction of touch on that hand

After a unilateral brain lesion, patients may show cross-modal, visual-tactile extinction. Such patients may fail to report tactile stimuli on the contralesional hand when presented together with competing visual stimuli near the ipsilesional hand. In this work we tested the hypothesis that this cross-modal extinction may be reduced when a patient has used a tool with the contralesional hand to reach for objects in the ipsilesional visual field. Consistent with previous work, we hypothesize that active use of a tool may extend cross-modal interactions between visual stimuli at the tip of the tool and tactile stimuli on the hand wielding the tool. In the new situation of a tool connecting the contralesional hand with ipsilesional visual space, competition between stimuli on these opposite sides may be reduced, so that extinction decreases. We studied patient BV, who showed reliable cross-modal, visual-tactile extinction after right-hemisphere stroke. In two separate sessions we showed that prolonged tool use (10-20 min) with the contralesional hand in ipsilesional space reduced cross-modal extinction for up to 60-90 min post-training. We propose that an actively used tool may be effective in linking cross-modal stimuli presented along its extension. This can then overcome competition between stimuli presented on opposite sides of the body midline, thus modulating extinction.