Abstract
Noisy galvanic vestibular stimulation (nGVS) can improve different motor, sensory, and cognitive behaviors. However, it is unclear how this stimulation affects brain activity to facilitate these improvements. Functional near-infrared spectroscopy (fNIRS) is inexpensive, portable, and less prone to motion artifacts than other neuroimaging technology. Thus, fNIRS has the potential to provide insight into how nGVS affects cortical activity during a variety of natural behaviors. Here we sought to: (1) determine if fNIRS can detect cortical changes in oxygenated (HbO) and deoxygenated (HbR) hemoglobin with application of subthreshold nGVS, and (2) determine how subthreshold nGVS affects this fNIRS-derived hemodynamic response. A total of twelve healthy participants received nGVS and sham stimulation during a seated, resting-state paradigm. To determine whether nGVS altered activity in select cortical regions of interest (BA40, BA39), we compared differences between nGVS and sham HbO and HbR concentrations. We found a greater HbR response during nGVS compared to sham stimulation in left BA40, a region previously associated with vestibular processing, and with all left hemisphere channels combined (p < 0.05). We did not detect differences in HbO responses for any region during nGVS (p > 0.05). Our results suggest that fNIRS may be suitable for understanding the cortical effects of nGVS.
Highlights
Subthreshold noisy galvanic vestibular stimulation is a non-invasive technique that delivers noisy, alternating electrical current through surface electrodes on the mastoid bones
We explored whether it is possible to monitor the effects of subthreshold noisy galvanic vestibular stimulation (nGVS) on cortical brain activity with Functional near-infrared spectroscopy (fNIRS) and how HbO and HbR concentrations are affected by this form of vestibular stimulation
The majority of participants in this study showed different cortical responses when they received nGVS versus sham stimulation
Summary
Subthreshold noisy galvanic vestibular stimulation (nGVS) is a non-invasive technique that delivers noisy, alternating electrical current through surface electrodes on the mastoid bones. This stimulation activates both vestibular hair cells and afferents of the otoliths and semicircular canals [1,2]. The effects of nGVS are likely the result of the fact that the vestibular afferents terminate in the vestibular nuclei, which can influence motor behavior through their connections with oculomotor circuitry and via the vestibulospinal tract [21,22,23]. Since the vestibular nuclei have dense connections with the thalamus, nGVS has the potential to affect a variety of brain regions and behavior [24]. Knowledge of how nGVS affects cortical activity is still limited
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