Hammam E., Dawood T., Macefield V. (2012). Low-frequency galvanic vestibular stimulation evokes two peaks of modulation in skin sympathetic nerve activity. Experimental Brain Research, 219: 441-446 Details
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For some, the gentle rocking motion of a boat can cause uneasiness, whilst in others it may provoke nausea, pale sweaty skin, altered breathing and even vomiting. To make matters worse, any natural tendency to seek out refuge in a cabin bed, for example, will aggravate the sickness due to heightened mismatch between vestibular and visual sensory streams.
Researchers at the University of Western Sydney have performed a number of studies to establish the connection between vestibular stimulation and physical symptoms of motion sickness. Macefield and colleagues use low-frequency sinusoidal galvanic vestibular stimulation (sGVS) to mimic slow body movement – sGVS itself can provoke feelings of nausea in people prone to motion sickness. Their previous studies have revealed that sGVS causes heightened muscular sympathetic nervous system activity.
In this study microneurography was used to monitor skin sympathetic activity (SSNA), recorded from the left common peroneal nerve using a NeuroAmp amplifier. Subjects received sGVS applied to the right mastoid process, i.e., near the peripheral vestibular organs. Sweat release and SSNA, along with blood pressure, ECG, respiratory rate and skin blood flow, were sampled and digitized with a PowerLab 16SP.
In all 11 subjects, sGVS gave the illusion of movement, such as the feeling of “rocking in a boat”. Analysis of SSNA bursts revealed two distinct processes: a large SSNA burst associated with the sGVS waveform peak, and a smaller SSNA burst associated with the sGVS waveform trough. This combined vestibular output is postulated to drive the medullary raphe to elicit SSNA responses.
These findings reveal how the vestibular system activates skin sympathetic outflow – accounting for the pallor and sweatiness in people with motion sickness. The authors also found that this effect was greater in subjects reporting nausea following sGVS, which supports the view that motion sickness may result from exaggerated vestibular-sympathetic reflexes.