REHABILITATION OF NEGLECT BY WEDGE PRISM ADAPTATION From sensorimotor adaptation to spatial cognition

Abstract

A large proportion of right-hemisphere stroke patients exhibit unilateral neglect, a neurological condition characterised by deficits for perceiving, attending, representing, and/or performing actions within their left-sided space. Unilateral neglect is responsible for many debilitating effects on everyday life, for poor functional recovery, and for decreased ability to benefit from treatment. Prism adaptation (PA) to a right lateral displacement of the visual field (induced by a simple target-pointing task with base-left wedge prisms) is known to directionally bias visuo-motor and sensory-motor correspondences and has recently been found to improve various symptoms of neglect. For example, performance on classical pen-and-pencil visuo-motor tests could be improved for at least two hours after adaptation. Effects of PA have also been described for non-motor and non-visual tasks, such as for somatosensory extinction, for deficits in mental imagery of geographic maps and in number bisection, and even for visuo-constructive disorders. These results suggest that the effects of prism adaptation can extend to unexposed sensory systems. The bottom-up approach of visuo-motor adaptation appears to interact with higher order brain functions related to multisensory integration and can have beneficial effects on sensory processing in different modalities. Lesion studies and functional imaging data point to a cerebello-cortical network in which each structure plays a specific role, though not necessarily one that is crucial for adaptation. Prism adaptation could act specifically not only on the ipsilesional bias characteristic of hemineglect but rehabilitates more generally the other spatial cognition deficits due to damage of the right hemisphere.