Cortical modulation of whole body movements in brain-damaged patients.

The aim of the present study was to assess whether the consistent bias in reproducing distances and lengths on visual tasks that characterizes hemispatial neglect is also present when whole body displacements have to be calculated and reproduced. Two different experiments were proposed to participants with right brain lesions and neglect syndrome (RN+), right (RN-) and left brain lesions (LN-) without neglect and to participants without brain damage (C). In Experiment 1, participants actively reproduced passive linear displacements in the same or in a different direction. This task could be performed using only vestibular and somatosensory input, since no relevant visual input was available. In Experiment 2, relevant visual information had to be integrated with vestibular and somatosensory information in order to make the active reproduction. In Experiment 1, all brain-damaged groups reproduced the horizontal displacements similarly to the control group and without any spatial asymmetry. In Experiment 2, when vestibular, somatosensory and visually remembered information was required to produce an integrated mental representation, RN+ processed contralesional displacements differently from ipsilesional ones. Rectilinear displacements of the whole body in space were not affected by focal left and right brain lesions, suggesting that the computation of nonvisual information can be accomplished by brain structures different from those involved in spatial visual processes. However, when body displacements in space required a mental representation based on visual and nonvisual sensory information, a significant asymmetry appeared only in patients with hemispatial neglect. Some attempts are made to identify the neural substrates involved in this integration.