Effects of galvanic stimulation of the mastoid process on the gastric motility induced by caloric stimulation

Visual Vestibular Conflict Mitigation in Virtual Reality Using Galvanic Vestibular Stimulation

BACKGROUND: Virtual reality (VR) is an effective technique to reduce cost and increase fidelity in training programs. In VR, visual and vestibular cues are often in conflict, which may result in simulator-induced motion sickness. The purpose of this study is to investigate the integration of Galvanic Vestibular Stimulation (GVS) with a VR flight training simulator by assessing flight performance, secondary task performance, simulator sickness and presence.METHODS: There were 20 participants who performed 2 separate VR flight simulation sessions, with and without GVS (control). Flight performance, secondary task performance, and electrogastrogram were measured during VR flight simulation. The standardized simulator sickness and presence questionnaires were administered.RESULTS: Electrogastrogram measures such as dominant power instability coefficient (DPIC) and percentages of bradygastric waves (%B) were lower in the GVS session than the control session in the flight simulation (DPIC: 0.44 vs. 0.54; %B: 21.2% vs. 30.5%) and postflight (DPIC: 0.38 vs. 0.53; %B: 22.8% vs. 31.4%) periods. Flight performance (#hit-gates) was improved in the GVS session compared to the control (GVS: 17, Control: 15.5). Secondary task performance (%hits) was improved with GVS for the Easy task (GVS: 55.5%, Control: 43.1%).DISCUSSION: This study demonstrates the potential of synchronizing GVS with visual stimuli in VR flight training to reduce visual-vestibular sensory conflict to improve fidelity and performance. These results provide initial evidence, but continued research is warranted to further understand the benefits and applications of GVS in VR simulator training.Pradhan GN, Galvan-Garza RC, Perez AM, Stepanek J, Cevette MJ. Visual vestibular conflict mitigation in virtual reality using galvanic vestibular stimulation. Aerosp Med Hum Perform. 2022; 93(5):406-414.

Role of peripheral vestibular receptors in the control of blood pressure following hypotension

Hypotension is one of the potential causes of dizziness. In this review, we summarize the studies published in recent years about the electrophysiological and pharmacological mechanisms of hypotension-induced dizziness and the role of the vestibular system in the control of blood pressure in response to hypotension. It is postulated that ischemic excitation of the peripheral vestibular hair cells as a result of a reduction in blood flow to the inner ear following hypotension leads to excitation of the central vestibular nuclei, which in turn may produce dizziness after hypotension. In addition, excitation of the vestibular nuclei following hypotension elicits the vestibulosympathetic reflex, and the reflex then regulates blood pressure by a dual-control (neurogenic and humoral control) mechanism. In fact, recent studies have shown that peripheral vestibular receptors play a role in the control of blood pressure through neural reflex pathways. This review illustrates the dual-control mechanism of peripheral vestibular receptors in the regulation of blood pressure following hypotension.

Nocebo Effects and Experimental Models in Visceral Pain

Despite its clinical relevance and the potential to extend insights into the processing and modulation of pain derived from investigations of placebo phenomena, the nocebo effect has received comparably little attention over the past decades. Research from experimental and clinical studies is only beginning to unravel the behavioral, functional, and psychoneurobiological mechanisms underlying the nocebo effect. Herein, we summarize current evidence regarding nocebo effects in the field of pain, with a particular emphasis on visceral pain. We provide an overview over behavioral and neuroimaging findings on the impact of expectations and learning and propose promising future directions to help fostering the transition of experimental research from bench to bedside.

Autonomic related vertigo

OBJECTIVES

To demonstrate clinical evidence that vestibular symptomatology can occur in relation to autonomic dysfunction. Characterization of clinical findings and treatment response would then allow autonomic related vertigo to be differentiated from other vertiginous conditions that present in a like manner.

STUDY DESIGN

This was a retrospective review of 113 patients that described symptoms consistent with spontaneous, rotational vertigo and autonomic dysfunction.

METHODS

Vestibular, otologic, and autonomic symptoms are presented along with the results of audiologic, orthostatic, and autonomic testing. Medical management included fluid loading, dietary changes, exercise, and patient education. Treatment results were analyzed according to the effectiveness in control of vestibular and otologic symptoms. Results were compared with a control group that demonstrated a similar vestibular and otologic presentation without autonomic symptomatology.

RESULTS

All patients described spontaneous, rotational vertigo, with complete or substantial vertigo control obtained in 93 (85%) of 110 patients. Postural vertigo and distinct lightheadedness were also documented in 53% and 97% of cases, respectively. Vertigo failed to improve or worsened with prior treatment of low sodium diet or diuretic in 53 (91%) of 58 cases. Vertigo improvement was subsequently achieved in 48 (86%) of 56 cases with an autonomic treatment regimen. Long-term vertigo control was obtained in 56 (88%) of 64 patients followed for at least 18 months. Tinnitus was reported in 97 (86%) patients, aural fullness in 93 (82%) patients, and subjective hearing loss (HL) in 46 (41%) of 111 cases. Bilateral tinnitus and aural fullness occurred in 65% and 63%, respectively. Tinnitus improved with treatment in 56 (67%) of 84 patients, whereas aural fullness improved in 59 (74%) of 80 patients. Autonomic symptoms included palpitations in 103 (91%) patients, chronic fatigue in 102 (90%) patients, cold extremities in 91 (81%) patients, and previous fainting in 72 (64%) patients. A history of mitral valve prolapse was documented in 51 (45%) of cases and demonstrated with echocardiogram in 68 (93%) of the 73 patients tested. Audiologic testing was normal in 104 (95%) of 109 patients, and electrocochleography was abnormal in 42 (40%) of 105 patients. Orthostatic blood pressure and heart rate testing met the criteria for orthostatic hypotension in 16 (15%) of 104 patients. Autonomic testing was obtained in 34 cases, with orthostatic intolerance demonstrated in 33 (97%) patients and orthostatic hypotension demonstrated in 13 (38%) patients. Overall, orthostatic hypotension was documented through combined testing results in 23 (21%) of 107 patients. Vertigo was reproduced during autonomic testing in 17 (77%) of 22 patients, and otologic symptoms were reproduce in 9 (47%) of 19 patients. Comparison of the study population with a control group without autonomic symptoms revealed statistically significant differences in orthostatic testing and treatment results. There was no statistical difference noted in findings between patients of this study that demonstrated or failed to demonstrate orthostatic hypotension.

CONCLUSIONS

There is a subgroup of patients with spontaneous vertigo who also demonstrate symptoms and findings consistent with poor autonomic regulation. These patients report vertigo improvement with a treatment strategy that aims to improve autonomic dysfunction through expansion of effective circulating volume. Clinical findings and treatment results of this study suggest an underlying autonomic influence in the production of vertigo and otologic symptoms.

Recovery of vestibulogastrointestinal symptoms during vestibular compensation after unilateral labyrinthectomy in rats

BACKGROUND

The loss of unilateral vestibular function causes vestibulogastrointestinal symptoms that include nausea and vomiting. However, the temporal changes occurring on vestibular compensation are unclear. Thus, the temporal changes and the role of the cerebellum in the recovery of vestibulogastrointestinal symptoms after unilateral labyrinthectomy (UL) were investigated in this study.

METHODS

Vestibulogastrointestinal symptoms were evaluated for intestinal transit and geometric center, whereas vestibulo-ocular symptoms were represented by spontaneous nystagmus. Expression of the c-Fos protein was observed in the vestibular nuclei. These were measured at 30 minutes and at 2, 6, and 24 hours after UL in rats.

RESULTS

Intestinal transit was 66.3% +/- 7.6% in the control animals but significantly decreased to 40.7% +/- 7.8%, 46.3% +/- 6.3%, and 48.6% +/- 10.8% at 30 minutes (p < 0.01), 2 hours (p < 0.01), and 6 hours (p < 0.05) after UL, respectively. The intestinal transit showed a recovery to control levels 24 hours after UL. The geometric center was 5.6 +/- 0.4 in control animals but significantly decreased to 2.1 +/- 0.4, 2.9 +/- 0.3, and 4.0 +/- 0.3 at 30 minutes, 2 hours, and 6 hours after UL, respectively (p < 0.01). Recovery of the geometric center to control levels, 24 hours after UL, was reported. Uvulonodullectomy significantly decreased the intestinal transit and geometric center for 24 hours after surgery (p < 0.01). Moreover, UL in uvulonodullectomized animals significantly decreased the intestinal transit and geometric center for 24 hours after surgery (p < 0.01). Pretreatment of the UL animals with MK-801 significantly increased the geometric center 30 minutes after surgery (p < 0.01). Unilateral labyrinthectomy produced spontaneous nystagmus, 28.9 +/- 1.5, 23.3 +/- 1.4, 17.5 +/- 1.5, and 9.2 +/- 0.9 beats per 10 seconds at 30 minutes and at 2, 6, and 24 hours after UL, respectively. Expression of the c-Fos protein was significantly increased in the medial vestibular nuclei and inferior vestibular nuclei at 1, 2, and 6 hours after UL, and the expression was significantly decreased in animals that were pretreated with MK-801 (p < 0.01).

CONCLUSION

These results suggest that the recovery of vestibulogastrointestinal symptoms is faster than that of vestibulo-ocular symptoms and that the cerebellum and glutamate have an important role to play in the recovery of symptoms after UL.

Differences in autonomic responses between subjects with and without nausea while watching an irregularly oscillating video

Prodromal signs such as cardiac rhythm disturbance and changes in gastric motility are generally induced before and during nausea in humans. These autonomic reactions were compared in subjects who were or were not experiencing nausea. Nausea was induced by having the subjects view a movie of oscillating pictures. Seventeen healthy volunteers were asked to relax their muscles and watch the movie. Electrogastrogram (EGG), electrocardiogram (ECG), palmar and metopic perspiration, digital blood flow and thoracic movement related to respiration were simultaneously measured while the subjects viewed the movie. A total of 11 of 17 subjects complained of nausea after watching the movie. The characteristic changes in their autonomic responses during exposure to the movie were as follows. The power of the EGG, heart rate and metopic perspiration significantly increased compared to those before watching the movie. The respiratory cycle gradually increased during and even after watching the movie. In contrast, no significant changes in the power of the EGG, heart rate and metopic perspiration were observed in the remaining six subjects who did not experience nausea. The role of the autonomic nervous system in nausea is discussed. These results suggest that these symptoms regarding the sympathetic nervous system could actually be defensive reactions against the sensation of nausea.

Localization of the mitochondrial uncoupling protein family in the rat inner ear

Uncoupling proteins (UCPs) are a proton transporter family located in the mitochondrial inner membrane. The molecular expression and activity of UCPs in brown adipose tissue and skeletal muscle are regulated by factors as diverse as chronic overeating and cold exposure, suggesting roles in energy expenditure and heat production. Although UCP2, UCP4 and brain mitochondrial carrier protein-1 (BMCP-1, i.e. UCP5) mRNAs are expressed in the central nervous system, their central function is unknown. This study presents the first evidence on localization and quantitative expression of UCPs in the rat inner ear by real-time PCR and immunohistochemistry. Real-time PCR studies revealed that UCP2 mRNA was expressed in the vestibular and spiral ganglia more abundantly than any other UCP. Neocortex, by contrast, contained UCP2 and UCP4 equally. Notably, UCP3 and UCP4 mRNAs were expressed in inner ear ganglia, but brain UCP3 mRNA expression level was undetectable by simple PCR. Immunohistochemical studies confirmed that both UCP2- and UCP3-like immunoreactivities were detected in vestibular and spiral ganglion cells and co-localized with a mitochondrial marker, MitoFluorGreen. According to previous reports, UCP2 and UCP3 are thermogenic in yeast and brain UCP2 has been suggested to modulate pre- and post-synaptic events by axonal thermogenesis. It has also been reported recently that UCP2 and UCP3 responses to superoxide application may be an antioxidant protective mechanism. Therefore, it is suggested that mitochondrial UCPs (UCP2, UCP3, UCP4) may play both a protective role against oxidative damage and a thermal signaling role in the eighth nerve.

Effects of acute hypotension on expression of cFos-like protein in the vestibular nuclei of rats

The expression and regional distribution of cFos protein, which is an oncogene product and metabolic marker of neural excitation, were investigated in the vestibular nuclear complex following acute hypotension in adult Sprague-Dawley rats. Intravenous administration of nitroprusside elicited a 10-50% reduction in mean blood pressure for 10 min. Unilateral or bilateral chemical labyrinthectomies were performed 14 days before the start of the experiment to eliminate afferent signals from the peripheral vestibular receptors in the inner ear. All of the animals were sacrificed and the tissues were fixed 2 h after the onset of acute hypotension using the cardiac perfusion method for c-Fos immunohistochemical staining. The cFos-like immunoreactive (cFLI) neurons were expressed selectively in the central area of the medial vestibular nucleus following a 10% reduction in blood pressure. Once the blood pressure had fallen by 30%, bilateral expression of cFLI neurons was observed in the superior, medial, and spinal vestibular nuclei, but not in the lateral vestibular nucleus, of control rats with intact labyrinths. The expression of cFLI neurons increased proportionately with reductions in blood pressure. In unilaterally labyrinthectomized rats, acute hypotension induced the expression of cFLI neurons in vestibular nuclei contra lateral to the injured labyrinth, but not in the ipsilateral vestibular nuclei. However, cFLI neurons were not expressed in bilateral vestibular nuclei following acute hypotension in bilateral labyrinthectomized rats. These results suggest that afferent signals from the peripheral vestibular receptors are essential for cFos protein expression in the vestibular nuclei following acute hypotension.

Effects of acute hypotension on neuronal activity in the medial vestibular nuclei of rats

The role of peripheral vestibular receptors in acute hypotension was investigated in anesthetized rats. In animals with intact labyrinths, acute hypotension induced by either i.v. infusion of sodium nitroprusside or hemorrhage produced excitation of electrical activity in two-thirds of type I neurons and inhibition in two-thirds of type II neurons recorded in the medial vestibular nuclei. In unilaterally labyrinthectomized animals, two-thirds of type I neurons ipsilateral to the lesion showed an inhibitory response, and two-thirds of contralateral type I neurons showed an excitatory response after the induction of acute hypotension. The response patterns of type II neurons were opposite to those of type I neurons. These results suggest that blood flow changes are detected by peripheral vestibular receptors, and that this might suggest a mechanism for control of blood pressure.