Effect of prism adaptation on neglect hemianesthesia

Prism adaptation (PA) has proven to be effective in alleviating many signs of unilateral spatial neglect (USN). Generally, the principal improvement after PA treatment was found to be in the high-level cognitive function. Nevertheless, some evidence has also been found for it in somatosensory function. We have aimed to test the influence of PA on neglect hemianesthesia, a condition in which the high-level neglect-related deficit mimics hemianesthesia. Twenty-one USN patients were enrolled in the study. Each patient performed two sessions of PA, one with neutral glasses and one with prism glasses using a cross-over design. Sensitivity on the upper limb was tested using two methods. The first task was the sensibility subtest which was derived from the standard clinical examination. The second was the perceptual and motor electro-cutaneous threshold on the forearms using an electro-cutaneous stimulator. Four neuropsychological tests were used to diagnose USN and to check improvement: Star cancellation, Line bisection, Sentence reading and the Comb & Razor test. Comparing prism with sham conditions, our results show significant improvements in double extinction and in the electro-cutaneous perceptual threshold only for the contralesional hand. No improvement was found for the ipsilesional hand, for the motor threshold, and for neutral glasses. Significant improvement was found in personal neglect. Replication of the task in a subgroup of patients confirmed the primary results. The improvements in somatosensory perception together with the amelioration of personal neglect suggest that PA also has a specific effect on the neglect hemianesthesia.