Passive limb movements improve visual neglect

Recent studies have reported that left neglect can be ameliorated during active movements of a contralesional limb in the contralesional space. In contrast, a passive left hand movement does not seem to induce an amelioration of neglect, at least when it is associated to simultaneous active right movement (Robertson IH, North N, Neuropsychologia 31 (1993) 293-300). In the present study, we explored the possibility that a complex passive movement, such as abduction and adduction of the arm, is able to reduce neglect also when it is associated to simultaneous active right arm movements. To test this hypothesis neglect patients were required to perform an object cancellation test and a line bisection test by using the right hand, while the left arm was passively moved. Moreover, we verified the possibility that left arm stimulation activates the peripersonal more than the extrapersonal space, with the exception of the condition in which the far space can be reached by a tool that extends peripersonal space in the far space (Farnè A, Làdavas E, Neuroreport 11 (2000) 1645-1649). For this reason, patients were required to perform the tasks in near (70 cm) and in far (140 cm) space by means of a light pen (pointing task) and of a stick (reaching task). When the left arm was passively moved the results showed a significant reduction of neglect with respect to the baseline condition, and the improvement equally affected the near and the far space. A different effect for the near and far space was observed in relation to the task (pointing vs. reaching). In the pointing task, neglect was more severe in the far than in near space; however, this difference disappeared when the patients had to reach objects by means of a stick. In conclusion, the present study shows that the entity of improvement of visual neglect due to a left passive movement is related to the entity of proprioceptive signals specifying left hand position.