Long-lasting amelioration of visuospatial neglect by prism adaptation

It has been shown that unilateral left neglect can be significantly improved for a short time after a short period of adaptation to a prismatic shift of the visual field to the right. In neuropsychological studies, however, there is no evidence demonstrating long-lasting effects following treatment by prism adaptation (PA). The first aim of the present study was to find out whether the short-term amelioration found after prismatic adaptation could be converted into long-term therapeutic improvement. Secondly, we investigated whether the improvement of neglect in standard tests could be generalized to ecological visuospatial tests. Thirdly, the effects of prism adaptation on different spatial domains (far, near and personal space) were evaluated. Fourthly, the influence of PA on high-order visuospatial functions, such as spatial representation, and on a low-order factor, i.e. sensory--motor bias, was investigated. Finally, we investigated the possible correlation between neglect amelioration, the adaptation effect and the visuomotor after-effect, as assessed by a pointing task during and after PA. Seven patients with right hemisphere lesion and left visuospatial neglect were treated with prismatic lenses in twice-daily sessions over a period of 2 weeks. In each training session, patients were required to perform a pointing task wearing base-left wedge prisms inducing a shift of the visual field to the right by 10. The presence of visual neglect and the duration of the amelioration achieved were assessed before the treatment and 2 days, 1 week and 5 weeks after treatment by using a standardized battery that included a series of behavioural and ecological visuospatial tests. Six control, untreated patients, matched to the experimental group for gravity and duration of illness, were submitted to the same tests at the same intervals as the experimental patients. The results showed an improvement in the experimental patients' performance after PA, which was maintained during the 5-week period after treatment. The amelioration of neglect was found in standard as well as in behavioural tests and in all spatial domains. In contrast, control patients did not show any improvement in neglect. The amelioration of neglect occurred only in patients who showed the adaptation effect and the after-effect in the pointing task. Neglect amelioration did not occur in one patient who did not show the adaptation effect and had an unstable after-effect. In conclusion, these findings show that prism adaptation is a productive way of achieving long-lasting improvements in neglect treatment.