Prism adaptation treatment of neglect: conflicting results?

In this issue of Neurology, two articles consider the treatment of neglect with prisms and initially appear to have contradictory results. 1,2 Neglect due to right hemisphere injury, most commonly after stroke, continues to be a major cause of disability, impairing ability to live independently and perform activities of daily living. Patients with strokes that damage the right hemisphere are more disabled than patients with left hemisphere injury and the major factor that leads to this disability is neglect. Thus there have been many attempts to find a means of teaching patients to attend to the neglected side of space. One means of improving the performance of patients with hemispatial neglect is to move stimuli into their body-centered ipsilesional space. 3 Therefore , providing patients with 15-diopter Fresnel prisms might be a simple means of shifting images to the normal side. Experimental subjects with neglect used these prisms for 4 weeks after which they were compared with control subjects who were not treated. 4 The treated group performed better than the untreated group in tasks such as line bisection or cancellation, thus demonstrating improvement on performance of some measures of attention to the neglected space, but the treated group's activities of daily living did not improve. To enhance the therapeutic effect of prisms, subjects were trained to point straight ahead while wearing the prisms. 5 This procedure has been called prism adaptation (PA). These PA-treated patients showed a reduction of ipsile-sional bias and the effects of treatment lasted for 2 hours after removal of the prisms. Another study revealed that PA can last for weeks, 6 but many questions about PA treatment remained unanswered. The two articles published in this issue of Neurolo-gy 1,2 answer some but not all of these questions and, of course, raise new questions. One theory suggests that PA may improve neglect by reducing ipsilateral intentional spatial bias and thereby helping with visual exploration. Maravita et al. 1 report four patients with neglect from right hemisphere strokes treated with PA, resulting in improvement on standard tests of spatial neglect. These subjects also showed improvement in their visual and tactile extinction and even tactile inattention (contralesional unawareness). The authors comment that their subjects' improvement cannot be entirely explained by an alteration of visual exploration because faulty exploration plays no apparent role in tactile extinction. Although the mechanisms of sensory extinction and contralateral sensory neglect are not entirely …