Grasso, P. A., Làdavas, E., & Bertini, C.
Compensatory Recovery after Multisensory Stimulation in Hemianopic Patients: Behavioral and Neurophysiological Components
Frontiers in Systems Neuroscience, 10
Lateralized post-chiasmatic lesions of the primary visual pathway result in loss of visual perception in the ﬁeld retinotopically corresponding to the damaged cortical area. However, patients with visual ﬁeld defects have shown enhanced detection and localization of multisensory audio-visual pairs presented in the blind ﬁeld. This preserved multisensory integrative ability (i.e., crossmodal blindsight) seems to be subserved by the spared retino-colliculo-dorsal pathway. According to this view, audiovisual integrative mechanisms could be used to increase the functionality of the spared circuit and, as a consequence, might represent an important tool for the rehabilitation of visual ﬁeld defects. The present study tested this hypothesis, investigating whether exposure to systematic multisensory audio-visual stimulation could induce long-lasting improvements in the visual performance of patients with visual ﬁeld defects. A group of 10 patients with chronic visual ﬁeld defects were exposed to audio-visual training for 4 h daily, over a period of 2 weeks. Behavioral, oculomotor and electroencephalography (EEG) measures were recorded during several visual tasks before and after audiovisual training. After audio-visual training, improvements in visual search abilities, visual detection, self-perceived disability in daily life activities and oculomotor parameters were found, suggesting the implementation of more effective visual exploration strategies. At the electrophysiological level, after training, patients showed a signiﬁcant reduction of the P3 amplitude in response to stimuli presented in the intact ﬁeld, reﬂecting a reduction in attentional resources allocated to the intact ﬁeld, which might co-occur with a shift of spatial attention towards the blind ﬁeld. More interestingly, both the behavioral improvements and the electrophysiological changes observed after training were found to be stable at a follow-up session (on average, 8 months after training), suggesting long-term effects of multisensory audio-visual training. These long-lasting effects seem to be subserved by the activation of the spared retino-colliculo-dorsal pathway, which promotes orienting responses towards the blind ﬁeld, able to both compensate for the visual ﬁeld loss and concurrently attenuate visual attention towards the intact ﬁeld. These results add to previous ﬁndings the knowledge that audio-visual multisensory stimulation promote long-term plastic changes in hemianopics, resulting in stable and long-lasting ameliorations in behavioral and electrophysiological measures.