Prism adaptation to a rightward optical deviation rehabilitates left hemispatial neglect

A large proportion of right-hemisphere stroke patients show hemispatial neglect-a neurological deficit of perception, attention, representation, and/or performing actions within their left-sided space(1), inducing many functional debilitating effects on everyday life, and responsible for poor functional recovery and ability to benefit from treatment(2). The frequent parietal locus of the lesion producing neglect reflects the impairment of coordinate transformation used by the nervous system to represent extrapersonal space. Given that adaptation to a visual distortion can provide an efficient way to stimulate neural structures responsible for the transformation of sensorimotor coordinates, the aim of our study was to investigate the effect of prism adaptation on various neglect symptoms, including the pathological shift of the subjective midline to the right. All patients exposed to the optical shift of the visual field to the right were improved on their manual body-midline demonstration and on classical neuropsychological tests. Unlike other physiological manipulations used to improve neglect, this improvement lasted for at least two hours after prism removal and thus could be useful in rehabilitation programmes. The positive effect found for both sensorimotor and more cognitive spatial functions suggests that they share or depend on a common level of space representation linked to multisensory integration.