Abstract
Spatial orientation necessitates the integration of visual and vestibular sensory cues, in-turn facilitating self-motion perception. However, the neural mechanisms underpinning sensory integration remain unknown. Recently we have illustrated that spatial orientation and vestibular thresholds are influenced by interhemispheric asymmetries associated with the posterior parietal cortices (PPC) that predominantly house the vestibulo-cortical network. Given that sensory integration is a prerequisite to both spatial orientation and motion perception, we hypothesized that sensory integration is similarly subject to interhemispheric influences. Accordingly, we explored the relationship between vestibulo-cortical dominance – assessed using a biomarker, the degree of vestibular-nystagmus suppression following transcranial direct current stimulation over the PPC – with visual dependence measures obtained during performance of a sensory integration task (the rod-and-disk task). We observed that the degree of visual dependence was correlated with vestibulo-cortical dominance. Specifically, individuals with greater right hemispheric vestibulo-cortical dominance had reduced visual dependence. We proceeded to assess the significance of such dominance on behavior by correlating measures of visual dependence with self-motion perception in healthy subjects. We observed that right-handed individuals experienced illusionary self-motion (vection) quicker than left-handers and that the degree of vestibular cortical dominance was correlated with the time taken to experience vection, only during conditions that induced interhemispheric conflict. To conclude, we demonstrate that interhemispheric asymmetries associated with vestibulo-cortical processing in the PPC functionally and mechanistically link sensory integration and self-motion perception, facilitating spatial orientation. Our findings highlight the importance of dynamic interhemispheric competition upon control of vestibular behavior in humans.
Highlights
Consider the following scenario: you are sat on a stationary train viewing the train on the adjacent platform which sets off
Posterior parietal cortex (PPC) (Dieterich et al, 2003; Lopez et al, 2012; Arshad, 2017), are required to resolve is whether: “I am moving?” or, “is the world moving?” Failure to resolve this sensory ambiguity can lead to disorientation, thereby demonstrating that sensory cue integration is a pre-requisite for both motion perception and maintaining spatial orientation (Guerraz et al, 2001; Karmali et al, 2013; Ward et al, 2017)
We have previously demonstrated that the degree of vestibular nystagmus suppression induced following cortical inhibition of the left posterior parietal cortex reflects the degree of vestibulo-cortical hemispheric dominance (Arshad et al, 2015a,b)
Summary
Consider the following scenario: you are sat on a stationary train viewing the train on the adjacent platform which sets off. Given the ecological importance of spatial orientation for survival, to-date a neuroscientific mechanism is currently lacking as to why some individuals rely more heavily upon visual cues (Witkin et al, 1975; Witkin and Goodenough, 1977), and others on vestibular (i.e. gravito-inertial cues) or somato-proprioceptive cues (Bronstein et al, 2013) In part such preferences for visual cues during sensory integration have been attributable to an individual's psychological trait (Witkin et al, 1975; Witkin and Goodenough, 1977), a notion supported by recent findings that demonstrate a close link between psychological factors (i.e. anxiety, body vigilance) and increased visual dependence in patients with acute unilateral vestibular loss (Cousins et al, 2014; Cousins et al, 2017)
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