Dynamic interhemispheric competition and vestibulo-cortical control in humans; A theoretical proposition.

Neuroscientific research has made a concerted effort to determine cortical localization using various functional imaging techniques. This approach has undoubtedly yielded important novel anatomical knowledge, albeit at times contradictory, regarding the structural organization of the vestibular cortex. Unfortunately however, this knowledge has not translated to our understanding regarding how neural mechanisms control vestibular function. Based upon recent functional imaging, lesion and neuro-physiological data that have demonstrated (i) the close behavioral and neuro-anatomical relationship between cortical processing of vestibular and spatial attention signals, and (ii) that inducing interhemispheric competition can in-turn strongly modulate vestibular function akin to that observed in cortical lesion patients, I herewith propose the hypothesis that vestibular cortical processing is controlled, as per for spatial attention, via dynamic interhemispheric competition. In the first half of this review I discuss previous key findings in the field of vestibular neuroscience that can be reinterpreted to support the role of interhemispheric competition for the control of high-level vestibular functions. Contrastingly, in the second half of this review, I present previous findings that show how disrupting interhemispheric interactions can modulate the brainstem-mediated vestibular-ocular reflex (VOR). I conclude by speculating why interhemispheric competition induces correlated biases at the cortical and brainstem level respectively. Specifically, I propose that brainstem-mediated vestibulo-spatial and vestibulo-temporal transformations, in addition to coding for head displacement, underpin a generalized cortical magnitude estimation system which the CNS uses to construct dynamic spatio-temporal maps of the physical world, in-turn ensuring spatial orientation.