Improvement of left visuo-spatial hemineglect by left-sided transcutaneous electrical stimulation.

The effects of transcutaneous electrical stimulation on left visuo-spatial hemineglect, assessed by a visuo-motor exploratory task (letter cancellation), were investigated in patients with right hemisphere lesions. In Experiment 1 left neck stimulation temporarily improved the deficit in 13 out of 14 patients (93%), while stimulation of the right neck had no positive effects, worsening exploratory performance in nine patients (64%). Experiment 2 showed that left neck stimulation temporarily improved neglect also when head movements were prevented by a chin-rest. In Experiment 3, stimulation of both the left hand and left neck had comparable positive effects on visuo-spatial hemineglect. These results are interpreted in terms of: (1) non-specific activation of the right hemisphere, contralateral to the stimulation side; (2) specific directional effects of left somatosensory stimulation on the egocentric co-ordinates of extra-personal space, which in neglect patients are distorted towards the side of the brain lesion.