Right hemisphere dominance directly predicts both baseline V1 cortical excitability and the degree of top-down modulation exerted over low-level brain structures

Abstract

HighlightsLine bisection predicts V1 excitability.Line bisection predicts degree of VOR modulation.Line bisection correlates with tDCS-mediated vestibular-nystagmus suppression.Degree of nystagmus suppression is a bio-marker of right hemisphere dominance.

Vestibulo‐cortical hemispheric dominance: The link between anxiety and the vestibular system?

“…Rather, it is the degree of cortically mediated suppression of the brainstem VOR that correlates with the anxiety scores, implying a cortically‐controlled re‐scaling of brainstem‐cortical interactions. In line with this, our previous findings have demonstrated that the nystagmus suppression index correlates with cognitive biases such as numerical magnitude perception and spatial attention (Arshad et al., , ), further supporting the notion of a brainstem‐cortical re‐scaling network.…”

“…With respect to vestibular processing, it has been shown that in right‐handed individuals predominant processing of vestibular signals occurs in the right hemisphere, whereas in left‐handers, the left hemisphere is dominant (Arshad et al., ; Dieterich et al., ; Nigmatullina et al., ). Furthermore, the degree of right hemisphere dominance in the vestibular system has been shown to influence both cortical (i.e., early visual cortex excitability) and brainstem (i.e., modulation of the vestibulo‐ocular reflex) functions (Arshad et al., ). Additionally, right hemisphere vestibulo‐cortical dominance has been shown to influence the modulation of vestibular thresholds following a change in cortical excitability (Bednarczuk et al., ).…”

“…This cortical area and montage were selected as it is strongly implicated in vestibular processing and has been shown to modulate vestibular responses (Bednarczuk, Casanovas Ortega, Fluri, Bronstein, & Arshad, ). We applied either unipolar cathodal (test condition) or anodal stimulation (control condition), which previous research has shown not to have any effect on vestibular processing and additionally provides an active control for any nonspecific effects associated with electrical stimulation(Arshad, Nigmatullina, & Bronstein, ; Arshad et al., , ).…”

“…Eye movements were analysed automatically by extracting the slow phase components of the vestibular nystagmus which were plotted over time to identify the peak slow phase velocity (SPV). Furthermore, to determine hemispheric dominance, we calculated the average change in the peak SPV following left hemisphere cathodal tDCS (test condition), to provide the nystagmus suppression index, which acted as a surrogate measure of hemispheric dominance (Arshad et al., ). Specifically, the formula implemented to calculate the nystagmus suppression index, involved dividing the peak post‐tDCS peak SPV minus the peak pre‐tDCS SPV by the peak pre‐tDCS SPV × 100.…”

“…Anxiety levels were determined using the trait component of the Spielberger State‐Trait Anxiety inventory (Spielberger, Vagg, Barker, Donham, & Westberry, ). Hemispheric lateralisation of the vestibular system was determined using a biomarker that assesses the degree to which a caloric‐induced vestibular nystagmus is suppressed following modulation of cortical excitability using trans‐cranial direct current stimulation (tDCS) applied over the posterior parietal cortex(Arshad et al., ), which is a key area in the vestibular cortical network. In conjunction, these measures will allow us to gage the nature of the relationship between anxiety networks and the vestibular system.…”