An audio-visual multisensory training reduces interhemispheric imbalance in hemianopic patients

Behavioral evidence has shown that hemianopic patients can exhibit an attentional bias towards the ipsilesional visual hemifield, which might represent a possible consequence of the disruption of the competition between the two hemispheres. The present study aimed to test whether hemianopics exhibit an interhemispheric imbalance and whether this could be reduced after an audio-visual training. To this aim, EEG activity during eyes-closed resting state has been recorded both on patients and on an age-matched control group (B1). In addition, patients have been re-tested after two weeks, i.e., immediately before training (control baseline 2: B2), and after the audio-visual training (POST). Clinical measures of visual search abilities, visual detection, self-perceived disabilities and oculomotor parameters were also collected before and after training. In the alpha range (8-12 Hz), at B1 hemianopic patients showed a significant greater power in the intact hemisphere, compared to the lesioned hemisphere, while controls showed no difference between the hemispheres. No significant difference in the beta (15-30 Hz) and theta (4-7 Hz) range was found between patients and controls. At POST, the results revealed a significant improvement in the clinical measures and also a significant reduction of the alpha power in the patients’ intact hemisphere, while no difference was found between B1 and B2. These results suggest the presence of an interhemispheric imbalance in hemianopic patients in the alpha range, which might reflect an imbalance of the dorsal attentional system. Moreover, an intensive audio-visual stimulation can concurrently improve the clinical signs of hemianopia and reduce this interhemispheric imbalance.