[Abstract] Interhemispheric visual competition after multisensory reversal of hemianopia

Abstract

Unilateral lesions of visual cortex have the secondary consequence of suppressing visual circuits in the midbrain superior colliculus (SC), collectively producing blindness in contralesional space (“hemianopia”). Recent studies have demonstrated that SC visual responses and contralesional vision can be reinstated by a non‐invasive multisensory training procedure in which spatiotemporally concordant visual‐auditory pairs are repeatedly presented within the blind hemifield. Despite this recovery of visual responsiveness, the loss of visual cortex was expected to result in permanent deficits in that hemifield, especially when visual events in both hemifields compete for attention and access to the brain’s visuomotor circuitry. This was evaluated in the present study in a visual choice paradigm in which the two visual hemifields of recovered cats were simultaneously stimulated with equally‐valent visual targets. Surprisingly, the expected disparity was not found, and some animals even preferred stimuli presented in the previously blind hemifield. This preference persisted across multiple stimulus intensity levels and there was no indication that animals were less aware of cues in the previously blind hemifield than in its spared counterpart. Furthermore, when auditory cues were combined with visual cues, the enhanced performance they produced on a visual task was no greater in the normal than in the previously blind hemifield. These observations suggest that the multisensory rehabilitation paradigm revealed greater inherent visual information processing potential in the previously blind hemifield than was believed possible given the loss of visual cortex.

 

via Interhemispheric visual competition after multisensory reversal of hemianopia – Dakos – – European Journal of Neuroscience – Wiley Online Library

[ARTICLE] Multisensory-Based Rehabilitation Approach: Translational Insights from Animal Models to Early Intervention – Full Text

Multisensory processes permit combinations of several inputs, coming from different sensory systems, allowing for a coherent representation of biological events and facilitating adaptation to environment. For these reasons, their application in neurological and neuropsychological rehabilitation has been enhanced in the last decades. Recent studies on animals and human models have indicated that, on one hand multisensory integration matures gradually during post-natal life and development is closely linked to environment and experience and, on the other hand, that modality-specific information seems to do not benefit by redundancy across multiple sense modalities and is more readily perceived in unimodal than in multimodal stimulation. In this review, multisensory process development is analyzed, highlighting clinical effects in animal and human models of its manipulation for rehabilitation of sensory disorders. In addition, new methods of early intervention based on multisensory-based rehabilitation approach and their applications on different infant populations at risk of neurodevelopmental disabilities are discussed.

Introduction

Human capacity to use different senses and combine different sources of information is key to understanding surrounding environment and gradually initiate adaptive behaviors. This synergy produces a percept whose reliability is much greater than a sum of information coming from different sensory channels and it is also a powerful asset in signal disambiguation, including human speech and animal communication. Facilitation of these competences has a large adaptive value and it is present in all extant species. The expression “Multisensory Integration” (MI) describes this neurobiological process, “by which information from different sensory systems is combined to enhance and accelerate detection, localization, and reaction to biologically significant events” (Stein et al., 2009).

This review aims to: (1) examine developmental trajectories of multisensory processes both in animal and human models; (2) highlight effects of a multisensory-based rehabilitation approach in adults and children with visual disorders; and (3) explore the potential effect of multisensory-based rehabilitation approach in the context of early intervention in children with some neurodevelopmental disabilities.

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Figure 1. Schematic view of loudspeakers and light displays position in the apparatus for audiovisual stimulation used by Bolognini et al. (2005) and Tinelli et al. (2015). The picture was designed by the authors of this review to explain the multisensory training approach for hemianopic patients. Training was performed with subjects sat in front of the apparatus in a dimly lit and sound-attenuated room and in binocular condition. Subjects were required to look at the fixation point (in the center of the apparatus), and to explore the blind hemifield by shifting their gaze toward visual stimulus, without any head movements. They were instructed to detect the presence of visual target by pressing a button and ignore any auditory stimuli. Fixation was monitored visually by the experimenter standing behind the apparatus, facing the subject. Three different kinds of sensory stimulation were presented: (i) unimodal visual condition; (ii) unimodal auditory condition; and (iii) crossmodal visual–auditory condition. In cross-modal condition, sound could be presented either in the same position as the visual stimulus, i.e., spatially coincident cross-modal condition, or in a different position, i.e., spatially disparate cross-modal condition, at 16 and 32° of nasal or temporal disparity from visual target. Treatment started with 500 ms of stimulus onset asynchrony (SOA) for cross-modal stimuli, i.e., the auditory stimulus preceded the visual target by 500 ms, and SOA was reduced in steps of 100 ms (i.e., 400, 300, 200, and 100 ms) up to the last session of training, in which stimuli were simultaneous (i.e., 0 ms of SOA). Each SOA session terminated when a hit ratio of at least 50% in unimodal visual condition was obtained. Treatment ended when subjects detected more than 50% of the unimodal visual stimuli for three consecutive blocks of trials in the simultaneous presentation of audiovisual stimuli (last SOA session).