Postural motion perception during vestibular stimulation depends on the motion perception threshold in persistent postural-perceptual dizziness.

Patients with persistent postural-perceptual dizziness (PPPD) perceive postural instability larger than the observed sway. It is unknown whether the concept of postural misperception prevails during vestibular stimulation and whether it may account for the unsteadiness patients complain during body movements. We tested the hypothesis of an abnormal sensory-perceptual scaling mechanism in PPPD by recording objective, perceived, and the reproduced postural sway under various standing conditions, modulating visual and proprioceptive input, by binaural galvanic vestibular stimulation (GVS). We related postural sway speed to individual vestibular motion perceptional thresholds and disease-related PPPD questionnaires in 32 patients and 28 age-matched healthy control subjects (HC). All participants showed normal vestibular function tests on quantitative testing at the time of enrollment. The perception threshold of GVS was lower in patients. Compared to HC, patients showed and perceived larger sway on the firm platform. With GVS, posturo-perceptual ratios did not show group differences. The ratio of reproduced to real postural sway showed no group differences indicating normal postural sway perception during vestibular stimulation. Noticeably, only in patients, reproduced postural instability became larger with lower individual thresholds of vestibular motion detection. We conclude that posturo-perceptual (metacognitive) scaling of postural control seems to be largely preserved in PPPD during GVS. Vestibular stimulation does not destabilize patients more than HC, even in challenging postural conditions. Low individual thresholds of vestibular motion perception seem to facilitate instability and postural misperception on solid grounds. This conclusion is important for an effective physical therapy with vestibular exercises in PPPD.