Vagus or Vagal Nerve Stimulation
Source: https://www.epilepsysociety.org.uk/
A newer and more invasive type of treatment now being considered in the treatment of Bipolar disorder is VNS or Vagal Nerve Stimulation.
Patients who undergo VNS are surgically-implanted with a device similar to a cardiac pacemaker which stimulates the vagus nerve with electrical signals at regular intervals. These signals minimize the rapid cycling of moods in Bipolar patients and have also proved helpful in treating anxiety disorders.