The Role of the Subcortical Dorsal Visual Pathway in the Recovery of Visual Field Defects

Lateralized post-chiasmatic lesions to the primary visual pathway result in loss of vision over the visual field retinotopically corresponding to the site of the lesion. Previous studies showed that a systematic audio-visual training could constitute an efficient tool for the rehabilitation of such disturbances as revealed by ameliorated clinical performances in various visual domains. The first part of the present dissertation aim to shed light on the substrates underlying multisensory mediated recovery of visual field defects. Experiment 1 and Experiment 2, demonstrated that a sustained audio-visual training can promote stable plastic neural changes within the cortex, likely reflecting an enhanced activity of those neural circuits connecting superior colliculus to cortical areas within the dorsal stream. The second part of the present dissertation aimed to shed light on the functionality and the characteristics of extrageniculate circuits targeting extrastriate visual areas within the dorsal stream. Experiment 3 and Experiment 4, suggested that these connections remain responsive even when a lesion prevents visual processing within the primary visual channel and that these connections could play a relevant role in the rapid processing of salient visual stimuli. Overall, the present experimental evidence suggest that visual processing depends on a variety of neural circuits and that a lesion to the primary visual pathway do not abolish the visual processing mediated by alternative routes. Moreover, activity within these routes could be exploited in a rehabilitative perspective, as revealed by ameliorated clinical performances and stable plastic neural changes induced by a systematic multisensory audio-visual training in hemianopic patients.