Galvanic vestibular stimulator for fMRI studies

Abstract

Introduction: Areas of the brain that are associated with the vestibular system can be activated using galvanic vestibular stimulation. These areas can be studied through a combination of galvanic vestibular stimulation with functional magnetic resonance imaging (fMRI). In order to provide an appropriate sequence of galvanic stimulation synchronous with the MRI pulse sequence, a specific electronic device that was built and assessed is presented. Methods: The electronic project of the GVS is divided in analog and digital circuits. The analog circuits are mounted in an aluminum case, supplied by sealed batteries, and goes inside the MRI room near to the feet of the subject. The digital circuits are placed in the MRI control room. Those circuits communicate through each other by an optical fiber. Tests to verify the GVS-MRI compatibility were conducted. Silicone (in-house) and Ag/AgCl (commercial) electrodes were evaluated for maximum balance and minimal pain sensations. fMRI experiments were conducted in eight human volunteers. Results: GVS-MRI compatibility experiments demonstrate that the GVS did not interfere with the MRI scanner functionality and vice versa. The circular silicone electrode was considered the most suitable to apply the galvanic vestibular stimulation. The 1 Hz stimulation sinusoid frequency produced the biggest balance and the less pain sensations when compared to 2 Hz. The GVS was capable of eliciting activation in the precentral and postcentral gyri, in the central sulcus, in the supplementary motor area, in the middle and inferior frontal gyri, in the inferior parietal lobule, in the insula, in the superior temporal gyrus, in the middle cingulate cortex, and in the cerebellum. Conclusion:This study shows the development and description of a neurovestibular stimulator that can be safely used inside the MRI scanner room without interfering on its operation and vice versa. The developed GVS could successfully activate the major areas involved with multimodal functions of the vestibular system, demonstrating its validity as a stimulator for neurovestibular research. To the best of our knowledge, this is the first work that shows the development and the construction of a galvanic vestibular stimulator that could be safely used inside the MRI room.

Interaction of brain areas of visual and vestibular simultaneous activity with fMRI

“…After the third LC filter, carbon wires were used to connect it to the electrodes. Circular silicone (9 cm 2 , in-house) electrodes were bilaterally positioned over the mastoid processes of the temporal bones (for more details about the equipment see Della-Justina et al 2014). Before placing the electrodes, the skin was cleaned with alcohol, and a conductive gel, soluble in water, was used to improve the conductance.…”

Galvanic Vestibular Stimulation (GVS) Augments Deficient Pedunculopontine Nucleus (PPN) Connectivity in Mild Parkinson's Disease: fMRI Effects of Different Stimuli

“…Sinusoidally oscillating stimuli may also activate irregular vestibular afferents (Gensberger et al, 2016 ) relying on voltage dependent K-channels (Eatock and Songer, 2011 ). While a couple of fMRI studies have shown sinusoidal GVS modulated activations in various brain regions (Della-Justina et al, 2014 ; Lee et al, 2016 ), GVS's influence on the PPN has not yet been investigated. A recent study in healthy older adults ( n = 20) found that noisy GVS resulted in sustained reduction in Centre of Pressure (COP) parameters, such as velocity, and Root Mean Square (RMS) (Fujimoto et al, 2016 ).…”

Vestibular Cortex

“…Vestibular activations have often been reported in the cingulate cortex, in both its anterior part (Brodmann areas 24/32) and posterior part (area 23) (Bense et al, 2001;Bottini et al, 1994;Della-Justina et al, 2014;Dieterich et al, 2003;Fasold et al, 2002;Miyamoto et al, 2007). Activations of the caudal part of the anterior cingulate cortex were also evident from a metaanalysis of vestibular activations (Lopez et al, 2012).…”

“…Vestibular activations were mainly found in the primary motor cortex and premotor cortex (Bense et al, 2001;Emri et al, 2003;Fasold et al, 2002;Lobel et al, 1998;Miyamoto et al, 2007), presumably in relation to the vestibular control of motor, postural, and oculomotor functions. The supplementary motor area, located in the medial surface of the frontal cortex, was also activated during CVS and GVS (Della-Justina et al, 2014;Smith et al, 2012;Wang et al, 2008). Additional vestibular activations in the dorsolateral prefrontal cortex, as well as in the middle/superior frontal gyri, may be related to vestibular processing in the frontal eye fields (FEF) (Bense et al, 2001;Dieterich et al, 2003;Miyamoto et al, 2007;Stephan et al, 2005).…”

“…The majority of fMRI, PET, and magnetoencephalography studies showed that CVS, GVS, and auditory stimulation activate the posterior and anterior insula, the parietal operculum, and the temporoparietal junction -including the superior temporal gyrus and inferior parietal lobule (Figures 2(b) and 3) (Bense et al, 2001;Bottini et al, 1994;Bucher et al, 1998;Della-Justina et al, 2014;Deutschländer et al, 2002;Dieterich et al, 2003;Eickhoff et al, 2006;Emri et al, 2003;Fasold et al, 2002;Hegemann et al, 2003;Indovina et al, 2005;Janzen et al, 2008;Marcelli et al, 2009;Schlindwein et al, 2008;Tuohimaa et al, 1983;Vitte et al, 1996;Wang et al, 2008;zu Eulenburg et al, 2013). All these regions located in the depth of, or around, the lateral sulcus could be the human equivalent of the monkey PIVC.…”