Representation of Body Orientation in Vestibular-Defective Patients Before and After Unilateral Vestibular Loss

Abstract

Introduction: The unilateral vestibular syndrome results in postural, oculomotor, perceptive, and cognitive symptoms. This study was designed to investigate the role of vestibular signals in body orientation representation, which remains poorly considered in vestibular patients.Methods: The subjective straight ahead (SSA) was investigated using a method disentangling translation and rotation components of error. Participants were required to align a rod with their body midline in the horizontal plane. Patients with right vestibular neurotomy (RVN; n =8) or left vestibular neurotomy (LVN; n = 13) or vestibular schwannoma resection were compared with 12 healthy controls. Patients were tested the day before surgery and during the recovery period, 7 days and 2 months after the surgery.Results: Before and after unilateral vestibular neurotomy, i.e., in the chronic phases, patients showed a rightward translation bias of their SSA, without rotation bias, whatever the side of the vestibular loss. However, the data show that the lower the translation error before neurotomy, the greater its increase 2 months after a total unilateral vestibular loss, therefore leading to a rightward translation of similar amplitude in the two groups of patients. In the early phase after surgery, SSA moved toward the operated side both in translation and in rotation, as typically found for biases occurring after unilateral vestibular loss, such as the subjective visual vertical (SVV) bias.Discussion and Conclusion: This study gives the first description of the immediate consequences and of the recovery time course of body orientation representation after a complete unilateral vestibular loss. The overall evolution differed according to the side of the lesion with more extensive changes over time before and after left vestibular loss. It is noteworthy that representational disturbances of self-orientation were highly unusual in the chronic stage after vestibular loss and similar to those reported after hemispheric lesions causing spatial neglect, while classical ipsilesional biases were reported in the acute stage. This study strongly supports the notion that the vestibular system plays a major role in body representation processes and more broadly in spatial cognition. From a clinical point of view, SSA appeared to be a reliable indicator for the presence of a vestibular disorder.

Ego- and Geo-Centered References: A Functional Neuroimagery Study

“…Comparing stroke patients, with or without spatial neglect, Rousseaux et al [8] showed that, in patients with spatial neglect, body representation alterations involved lesions of the inferior parietal cortex and the middle part of the superior temporal gyrus. It is interesting to note here that these cortical structures are also areas of vestibular projections, which could explain the disturbance of the SSA in patients with vestibular impairment [9][10][11]. Another result of the present study was the involvement of the cerebellum in body representation.…”

“…In stroke patients, in particular in those suffering from spatial neglect, damage of the same right cortical structures proved to be involved in ipsilesional SSA deviation [7, 8]. An ipsilesional SSA deviation has also been observed after unilateral peripheral vestibular injury, in particular after left injury [9‒11]. As they have been shown to be vestibular projection areas, the aforementioned cortical areas could be involved, which remains an open issue.…”

Vestibular perceptual testing from lab to clinic: a review

“…Interestingly, individuals with UVH perform with similar spatial accuracy compared with healthy individuals, regardless of presence of dizziness. Intact vestibular function is linked to the ability to represent external space as well as accurate body spatial schema ( 122 – 124 ). This may explain why individuals with unilateral vestibular loss perform at levels similar to healthy individuals.…”