Visual and vestibular motion perception in persistent postural-perceptual dizziness (PPPD)

Abstract

Persistent postural-perceptual dizziness (PPPD) is a chronic disorder of perceived unsteadiness. Symptoms can be exacerbated in visually complex stationary or moving environment. Visual dependence and increased motion sensitivity are predictors for PPPD but its pathophysiology remains unknown. We hypothesized an abnormal sensory–perceptual scaling mechanism in PPPD and tested visual- and vestibular perceptional thresholds in 32 patients and 28 age-matched healthy control subjects (HC). All participants showed normal vestibular function tests on quantitative testing. Visual motion coherence thresholds were assessed by random dot kinetomatograms. Vestibular perceptional thresholds of egomotion were assessed by binaural galvanic vestibular stimulation (GVS) and passive chair rotation around an earth-vertical axis. Chair rotation trials were contrasted with no-motion (sham) stimulus trials. Mean thresholds of visual motion perception were higher in patients compared to HC. The perception threshold of GVS was lower in patients but the threshold of correctly perceived egomotion during chair rotation did not differ. Interestingly, the number of trials with correct perception in the no-motion condition increased with the threshold of correct responses for rotatory egomotion in patients. Unlike expected, PPPD patients required more coherently moving random dots than HC to perceive visual motion. A poorer complex visual motion recognition, e.g., traffic visual stimuli, may increase anxiety and levels of uncertainty as visuomotor reactions might occur delayed. The vestibular rotatory perception threshold predicted the probability of making false assignments in the sham condition in PPPD, i.e., patients who readily recognize the correct egomotion direction are prone to perceive egomotion in the no-motion condition. As this relation was not found in healthy subjects, it may reflect an abnormal sensory–perceptual scaling feature of PPPD.

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

“…This visual dependence resembles functional neural reorganization in patients who suffered from unilateral vestibulopathy with subsequently developing abnormal visual impact on vestibular perception during the course of the disease [16,17]. In PPPD, we recently demonstrated poorer visual motion detection in PPPD [11]. Vestibular motion perception thresholds are lower during binaural galvanic vestibular stimulation but not during rotatory vestibular stimulation around the earth-vertical axis [11,12].…”

“…Age-matched healthy subjects had no history of vertigo, dizziness, migraine or other types of balance disorders. Most of the subjects participated in a related study investigating their visual and vestibular motion perception thresholds [11]. Demographics and patient characteristics are summarized in Table 1, including questionnaires addressing motion sickness susceptibility, dizziness intensity, impact on daily life, level of anxiety, depression, and personality features.…”

“…The skin surface was cleaned again and dried before contact electrodes with commercial contact paste were attached above the mastoid bilaterally. Individual sensory (vestibular) thresholds were obtained by applying 10 s 1 Hz alternating stimulation, i.e., low-frequency alternating current which passed between the two mastoid electrodes [11]. The ramp stimulus profile hampered sharp transients at stimulus onset and offset (ramp onset and offset of 100-ms duration) with a stimulation plateau of 300 ms leading to perceived head and body tilt.…”

“…A mismatch between 'bottom-up' (vestibular/proprioceptive sensory) inputs and maladaptive signals from 'top-down' attentional control systems has been suggested to determine perceived postural imbalance [8]. One trigger may come from altered thresholds of sensory (visual, vestibular, proprioceptive) motion perception, which have been studied in response to galvanic vestibular stimulation [9], to passive rotatory turntable [10,11] or rotatory roll tilt or translational z-vestibular motion [12].…”

“…In PPPD, we recently demonstrated poorer visual motion detection in PPPD [11]. Vestibular motion perception thresholds are lower during binaural galvanic vestibular stimulation but not during rotatory vestibular stimulation around the earth-vertical axis [11,12].…”