The peripheral nervous system is the nerves from the spinal cord to muscles and organs. Nerves to muscles are ones we use to play tennis, type on the computer, or move our eyes to read these words. There is also the autonomic nervous system for controlling organ function such as heart rate, gut motility, and bladder. The Vagus Nerve is one and originates in the brainstem just above the neck. It travels far down into the abdominal cavity, making connections to the heart, lungs, and stomach. Not only does it send impulses to organs, it also relays information back to the brain, making it both afferent and efferent.
In the late 70s it was discovered that pulsing the Vagus Nerve with small electric currents could help reduce seizures in some forms of epilepsy. So, Cyberonics began selling a small device similar to a cardiac pacemaker that could be implanted into patients’ chests – Vagus Nerve Stimulators, or VNS. Many people with seizure disorders do not have seizures adequately controlled with medication, so must rely on alternative treatments.
It was noted that some patients with depression in addition to epilepsy showed an improvement in depression regardless of any improvement in seizure control. Soon, VNS devices were being implanted in patients suffering only from depression.
There is no question this treatment is effective for a small number of patients. The question that still is not understood is why this should be.