By Emma Young
When we think of ways to calm ourselves via our senses, the obvious is to listen to relaxing music, have a massage, or perhaps to gaze upon a rustic scene. However, evidence is growing for a far less obvious option involving the vestibular system (located in the inner ear), which detects the position and movement of the head. According to a recent study, gentle rocking helps adults to fall asleep for a nap, and to sleep more soundly during an entire night, with the researchers who conducted that research hypothesising that the effect is driven by the vestibular system. Now new exploratory work by a different team provides further hints that stimulating the vestibular system can help to calm the brain — in this case, apparently reducing anxiety.
For the new study in Frontiers in Systems Neuroscience, led by Florane Pasquier at the University of Caen Normandy, the 22 healthy young adult participants weren’t physically rocked. Rather, electrodes, placed behind their ears, delivered a very mild, 1mA current to stimulate the nerves that carry signals from the individual components of the vestibular system to the brain. This technique is called galvanic vestibular stimulation (GVS).
The student participants took part in three sessions, each one held at the same time on the same day each week for three weeks. One was a 38-minute sham session during which no current was used; another involved 38 minutes of GVS, while the last involved 76-minutes of the stimulation (participants completed the different sessions in a randomised order). Before and after each session, the participants indicated on a visual scale how relaxed or tense they felt (as a simple measure of their anxiety levels), and also reported any feelings of motion sickness (a conflict between signals from the vestibular system versus the eyes and other sensory receptors in the body is thought to cause motion sickness.)
Only one session was associated with a significant decrease in the anxiety measure the researchers reported: the shorter, 38-minute period of stimulation. This was associated with a drop of about one quarter in the anxiety measure, post- vs pre-test, whereas there was no drop after the sham treatment, and only a hint of a much smaller drop after the double-duration stimulation. Pasquier’s team suspect that the electrical stimulation of neurons from the vestibular system may simulate the effects of gentle rocking, as in a train or car — something that can make many of us, whether adults or children, feel drowsy. “A possible hypothesis is the sedative effect of GVS on arousal state,” the researchers write.
The results are consistent with other studies that have also found vestibular stimulation can affect mood. For example, one that found swinging on a swing improved the anxiety levels of university students.
Why didn’t the longer session of GVS work? It’s not clear. Perhaps a clue comes from the fact that after a 76-minute session — but not the shorter 38-minute session— some participants reported feeling motion sickness.
Clearly, this is preliminary research. The anxiety measure was simple, and the study was conducted on a small number of young adults who didn’t report having any anxiety problems. Might a shorter session reduce anxiety scores, too? Is the apparent anxiety effect sustained, and if so, for how long? Could GVS make any real-world difference to people suffering from an anxiety disorder, or who are about to go into an anxiety-provoking situation, and is it 100 per cent safe? Only future research will tell.