Neurobiology of persistent perceptual postural dizziness (PPPD): Effects of galvanic vestibular stimulation (GVS) on behavioral, psychophysical, functional and structural brain imaging parameters

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Persistent persistent postural-perceptual dizziness (PPPD) is a very common dizziness disorder with enormous psychosocial burden that has been classified by the Barany Society in 2017. Patients complain about chronic postural and gait imbalance in the absence of quantitative sensory or cerebellar abnormalities. Typically, attentional distraction modulates postural imbalance and its perceived intensity. Among several pathophysiological hypotheses increased sensitivity to visual stimuli (exacerbation in visually demanding environments) with intersensory re-weighting of sensory processing and impaired updating of internal prediction models appear feasible ones. None of the previous studies, however, has elucidated brain activity in response to vestibular stimuli evoking a similar perception of one’s own body sway that is characteristic for PPPD. This is a main objective of this project proposal by means of galvanic vestibular stimulation (GVS). We will use sensory and inter-sensory (visual-vestibular) activity patterns to identify scaling mechanisms on a neuronal (event-related fMRI, functional connectivity), behavioral (posturography) and a perceptual level (perceived motion) and their interactions that may account for the clinical severity of PPPD. The relation of clinical and psychiatric scores will shed light on the clinical meaning of altered scaling mechanisms. The influence of prediction and self-control of the vestibular stimuli as well as attentional distraction on the brain activity will be examined in additional cognitive experiments. These are clinical feature that typically modify behavior in PPPD. At the end we hope to provide a model how internal expectations dominate sensory processing as driving force in PPPD. The patient’s reliance on previously formed but inaccurate expectations will make the perceived sensory (vestibular) input inadequate, insufficient to incorporate experimental stimulus variability and presumably the update of motor commands dysfunctional, e.g. by producing limb stiffness leading to postural imbalance.