Abstract
Background Activating vestibular afferents via galvanic vestibular stimulation (GVS) has been recently shown to have a number of complex motor effects in Parkinson's disease (PD), but the basis of these improvements is unclear. The evaluation of network-level connectivity changes may provide us with greater insights into the mechanisms of GVS efficacy. Objective To test the effects of different GVS stimuli on brain subnetwork interactions in both health control (HC) and PD groups using fMRI. Methods FMRI data were collected for all participants at baseline (resting state) and under noisy, 1 Hz sinusoidal, and 70-200 Hz multisine GVS. All stimuli were given below sensory threshold, blinding subjects to stimulation. The subnetworks of 15 healthy controls and 27 PD subjects (on medication) were identified in their native space, and their subnetwork interactions were estimated by nonnegative canonical correlation analysis. We then determined if the inferred subnetwork interaction changes were affected by disease and stimulus type and if the stimulus-dependent GVS effects were influenced by demographic features. Results At baseline, interactions with the visual-cerebellar network were significantly decreased in the PD group. Sinusoidal and multisine GVS improved (i.e., made values approaching those seen in HC) subnetwork interactions more effectively than noisy GVS stimuli overall. Worsening disease severity, apathy, depression, impaired cognitive function, and increasing age all limited the beneficial effects of GVS. Conclusions Vestibular stimulation has widespread system-level brain influences and can improve subnetwork interactions in PD in a stimulus-dependent manner, with the magnitude of such effects associating with demographics and disease status.
Highlights
Parkinson’s disease (PD) is characterized by motor symptoms of rigidity, tremor, bradykinesia, and nonmotor symptoms such as affective disorders and cognitive decline
We investigate the interactions between subnetworks with nonnegative canonical correlation analysis (CCA) and evaluate the effects of different galvanic vestibular stimulation (GVS) stimuli in subjects with PD
Most of the PD subjects had mild tremor and rigidity, and none of them presented freezing of gait. e detailed demographic data are provided in Table 1 and the subscores of tremor, rigidity, bradykinesia, and gait/posture are further described in Table 2. e study was approved by the University of British Columbia (UBC) Ethics Review Board and all the participants provided written, informed consent prior to the experiment
Summary
Parkinson’s disease (PD) is characterized by motor symptoms of rigidity, tremor, bradykinesia, and nonmotor symptoms such as affective disorders and cognitive decline. Galvanic Vestibular Stimulation (GVS) is a safe and potential portable brain stimulation technique to noninvasively activate vestibular afferents by applying weak electrical currents to the mastoid processes behind the ears. It influences downstream activity in both the vestibular network and regions associated with multisensory processing. Activating vestibular afferents via galvanic vestibular stimulation (GVS) has been recently shown to have a number of complex motor effects in Parkinson’s disease (PD), but the basis of these improvements is unclear. Vestibular stimulation has widespread system-level brain influences and can improve subnetwork interactions in PD in a stimulus-dependent manner, with the magnitude of such effects associating with demographics and disease status
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