Gravity and hemineglect

Spatial cognition requires the integration of visual inputs with proprioceptive and vestibular information about the position of the eye, the head and the body. All these sources are used by the brain to produce multiple higher-order (e.g. egocentric) representations of space, subserving accurate spatial behaviour. Such spatial representations are disrupted by unilateral cerebral damage producing neglect in the contralateral side of space. In eight brain-damaged patients with left unilateral neglect the manipulation of gravitational-otolithic information, obtained by placing patients in a supine position, produced a significant reduction of the rightward directional error in the line bisection task in all cases. This finding suggests that, in patients with neglect, gravitational information is processed in a non-symmetrical fashion, with a rightward bias towards the side of the lesion. This is the first study showing that manipulation of gravitational input affects neuropsychological disorders of visuo-spatial processing.