Prism adaptation and neck muscle vibration in healthy individuals: are two methods better than one?

Studies involving therapeutic combinations reveal an important benefit in the rehabilitation of neglect patients when compared to single therapies. In light of these observations our present work examines, in healthy individuals, sensorimotor and cognitive after-effects of prism adaptation and neck muscle vibration applied individually or simultaneously. We explored sensorimotor after-effects on visuo-manual open-loop pointing, visual and proprioceptive straight-ahead estimations. We assessed cognitive after-effects on the line bisection task. Fifty-four healthy participants were divided into six groups designated according to the exposure procedure used with each: 'Prism' (P) group; 'Vibration with a sensation of body rotation' (Vb) group; 'Vibration with a move illusion of the LED' (Vl) group; 'Association with a sensation of body rotation' (Ab) group; 'Association with a move illusion of the LED' (Al) group; and 'Control' (C) group. The main findings showed that prism adaptation applied alone or combined with vibration showed significant adaptation in visuo-manual open-loop pointing, visual straight-ahead and proprioceptive straight-ahead. Vibration alone produced significant after-effects on proprioceptive straight-ahead estimation in the Vl group. Furthermore all groups (except C group) showed a rightward neglect-like bias in line bisection following the training procedure. This is the first demonstration of cognitive after-effects following neck muscle vibration in healthy individuals. The simultaneous application of both methods did not produce significant greater after-effects than prism adaptation alone in both sensorimotor and cognitive tasks. These results are discussed in terms of transfer of sensorimotor plasticity to spatial cognition in healthy individuals.