Multisensory Training Rehabilitates Hemianopia

Unilateral damage to visual cortex produced by stroke or other injury commonly results in a profound contralateral blindness (hemianopia). This condition is largely regarded as a permanent disorder after six months and currently there are few effective methods for its rehabilitation. We have developed a promising non-invasive sensory rehabilitation paradigm using an established animal model in which all contiguous areas of visual cortex are lesioned. The paradigm involves the repeated presentation of spatiotemporally congruent visual-auditory stimuli in the blinded field, which engages the brain’s inherent mechanisms for multisensory processing and plasticity. The repeated coupling of visual and auditory signals boosts visual sensitivity within the intact ipsilesional secondary visual pathway, rapidly (within weeks) restoring visual responsiveness in the multisensory output layers of the superior colliculus and visually-guided behaviors everywhere in contralesional space. The rehabilitated visual capabilities include rudimentary pattern discrimination and are robust to competitive stimuli presented simultaneously in the intact field. Stimuli that do not engage the same mechanisms of multisensory plasticity (single visual or auditory stimuli and spatially or temporally incongruent pairings) were not effective in rehabilitation. To determine if this technique represented an effective rehabilitative approach for humans, two patients rendered hemianopic by stroke were recruited for a study. Patients were given repeated exposure to spatiotemporally congruent visual-auditory stimuli in their blinded field in weekly sessions and, within weeks, recovered the ability to detect and localize lights presented alone. This detection was robust to competition from the intact field. Patients could describe some features of visual stimuli in the rehabilitated field and reported substantial improvements in quality of life. These results provide proof-of-concept that multisensory training represents a viable, effective technique for the rehabilitation of hemianopia in human patients.