In search for the egocentric reference. A neurophysiological hypothesis

Vestibulo-ocular and optokinetic impairments in left unilateral neglect

“…It has been suggested that higher cortical and subcortical structures receiving vestibular inputs participate in multimodal coding of space and can, in turn, influence the vestibulo-ocular response [25,33,64]. We found that neglect patients suffering from defective coding of the contralesional left hemispace due to damage in the right hemisphere, have higher frequency of ipsilesional-slow/contralesional-fast phases and higher contralesional shift of the beating field of the VOR.…”

“…They found decrease of ipsilesional gain, increase of contralesional gain and spontaneous nystagmus with slow phases directed contralesionally. Developing the pioneering observations made by Hecaen and Massonet [35], Ventre et al [64] interpreted the predominance of slow phases toward the contralesional space as a compensatory response of the vestibular system to counteract the ipsilesional displacement of visuomotor behaviour produced by the unilateral lesion. According to the "egocentric reference" hypothesis (Ventre et al [64]), the ipsilesional bias of visuomotor behaviour is due to interhemispheric unbalance in the activation of multimodal representations of space usually ensuring symmetry of orienting and the alignment of the subjective sagittal body midline to the objective one.…”

“…Developing the pioneering observations made by Hecaen and Massonet [35], Ventre et al [64] interpreted the predominance of slow phases toward the contralesional space as a compensatory response of the vestibular system to counteract the ipsilesional displacement of visuomotor behaviour produced by the unilateral lesion. According to the "egocentric reference" hypothesis (Ventre et al [64]), the ipsilesional bias of visuomotor behaviour is due to interhemispheric unbalance in the activation of multimodal representations of space usually ensuring symmetry of orienting and the alignment of the subjective sagittal body midline to the objective one. Our results show that patients with extensive unilateral brain damage and chronic contralesional neglect have no contralesional bias in the gain of the VOR, suffer reduced frequency of contralesionally directed slow phases and show contralesional rather than ipsilesional deviation of the beating field.…”

“…In the intact organism, this frame of reference is aligned to the sagittal body midline and is used to code the left and right horizontal hemispace [3,62,63]. Ventre et al [64] found reduced gain and frequency of ipsilesionally directed horizontal VOR and spontaneous contralesional nystagmus in monkeys and cats with neglect due to unilateral parietal or collicular ablations. According to Ventre et al [64], these modifications of the VOR should not be considered as primary symptoms but, rather, as secondary effects of unilateral disruption of the neural system providing a balanced multimodal representation of the space lying on the two sides of the body midsagittal plane.…”

“…Ventre et al investigated the VOR in cats with unilateral ablations of the middle suprasylvian gyrus and superior colliculus [64] and in monkeys with unilateral ablation of area 7a [65]. They found decrease of ipsilesional gain, increase of contralesional gain and spontaneous nystagmus with slow phases directed contralesionally.…”