Long-lasting reduction in postural asymmetry by prism adaptation after right brain lesion without neglect

Right brain damage (RBD) involves postural asymmetry and spatial frame disorders. In acute RBD patients, postural asymmetry is immediately reduced after one single session of prism adaptation (PA), without assessment of effects on spatial frames.

To assess long-term effects of PA on posture and spatial frames in chronic RBD patients, without neglect.

Six chronic RBD patients without neglect (mean delay 45 months) were included. Each patient sustained 10 PA sessions of 20 min during 2 weeks. Outcome measures were: (1) posturographic analysis (mediolateral position of centre of pressure (X cop), (2) subjective straight ahead (SSA) and perception of longitudinal body axis (LBA). Each parameter was assessed by three pretests and three post-tests (+2 h, day + 3 and day + 7).

In pretests, patients showed a shift of the X cop and SSA. In post-tests, results displayed (1) a significant reduction in mediolateral postural asymmetry at D + 7; (2) a significant left deviation of SSA at D + 3 and enduring at D + 7; and (3) no significant modification of LBA. The mean curves of X cop and SSA between pre- and post-tests were similar.

PA involves persistent reduction in postural asymmetry in RBD patients without neglect. These findings were obtained at a chronic stage. This new effect cannot be explained by reduction in spatial attentional shift. Improvement may be explained by a better calibration of extra personal space frames used for posture, without effect on personal space frame. Findings argue in favour of a bottom-up effect of PA on mechanisms underlying spatial cognition.