over time. Also, side effects can be controlled by changing the stimulation parameters. There is evidence that VNS can induce sleep apnea in as many as 28% of adult patients. Devices and procedures The device consists of a generator the size of a matchbox that is implanted under the skin below the person’s collarbone. Lead wires from the generator are tunnelled up to the patient’s neck and wrapped around the left vagus nerve at the carotid sheath, where it delivers electrical impulses to the nerve. Implantation of the VNS device is usually done as an out-patient procedure. The procedure goes as follows: an incision is made in the upper left chest and the generator is implanted into a little "pouch" on the left chest under the collarbone. A second incision is made in the neck, so that the surgeon can access the vagus nerve. The surgeon then wraps the leads around the left branch of the vagus nerve, and connects the electrodes to the generator. Once successfully implanted, the generator sends electric impulses to the vagus nerve at regular intervals. The left vagus nerve is stimulated rather than the right because the right plays a role in cardiac function such that stimulating it could have negative cardiac effects. The "dose" administered by the device then needs to be set, which is done via a magnetic wand; the parameters adjusted include current, frequency, pulse width, and duty cycle. "Wearable" devices are being tested and developed that involve transcutaneous stimulation and do not require surgery. Electrical impulses are targeted at the aurical (ear), at points where branches of the vagus nerve have cutaneous representation; such devices had been tested in clinical trials for treatment resistant major depressive disorder as of 2017. History Early History James L. Corning (1855-1923) was an American neurologist who developed the first device for stimulating the vagus nerve towards the end of the 19th century. At that time a widely held theory was that excessive blood flow caused seizures. In the 1880s Corning designed a pronged instrument called the “carotid fork” to compress the carotid artery for the acute treatment of seizures. In addition, he developed the “carotid truss” for prolonged compression of the carotid arteries as a long-term preventative treatment for epilepsy. Then he developed the “electrocompressor” which allowed for the compression of the bilateral carotid arteries as well as electrical stimulation of both the vagus and