"Brain pacemakers" are used to treat people who suffer from epilepsy, Parkinson's disease, major depression and other diseases. The pacemaker is a medical device that is implanted into the brain to send electrical signals into the tissue. Depending on the area of the brain that is targeted, the treatment is called deep brain stimulation, or cortical stimulation. Brain stimulation may be used both in treatment and prevention. Pacemakers may also be implanted outside the brain, on or near the spinal cord (spinal cord stimulation), and around cranial nerves such as the vagus nerve (vagus nerve stimulation), and on or near peripheral nerves.
Epilepsy refers to a wide variety of neurological disorders characterized by sudden recurring attacks of motor, sensory, or psychic malfunction with or without loss of consciousness or convulsive seizures. The implantation of pacemakers in the brain may control or eliminate epileptic seizures with programmed or responsive stimulation.
Parkinson's disease 
The deep brain stimulation used in pacemakers to treat Parkinson's disease can help reduce symptoms such as tremors, rigidity, stiffness, slowed movement, and walking problems. The procedure also treats essential tremor, a neurological movement disorder. After the pacemaker is surgically implanted into the brain, electrical impulses are sent to the stimulator and into the brain. The procedure is generally only used for patients whose symptoms cannot be controlled with medication. The exact mechanism of action of DBS is not known. There exist three hypotheses to explain the mechanisms of DBS:
- Depolarization blockade: Electrical currents block the neuronal output at or near the electrode site.
- Synaptic inhibition: This causes an indirect regulation of the neuronal output by activating axon terminals with synaptic connections to neurons near the stimulating electrode.
- De-synchronization of abnormal oscillatory activity of neurons.
Deep brain stimulation represents an advance on previous treatments which involved pallidotomy (i.e., surgical ablation of the globus pallidus) or thalamotomy (i.e., surgical ablation of the thalamus). Instead, a thin electrode with four contacts is implanted in the globus pallidus, nucleus ventralis intermedius thalami (Vim) or the subthalamic nucleus and electric pulses are used to block the abnormal activity. The lead from the implant is extended to the pacemaker under the skin in the chest area.
Clinical depression 
Pacemakers are also being used to treat depression. Electrical stimulation has been shown to eliminate chronic depression in some patients. Some patients report an immediate improvement in mood and in their sleeping habits after implantation. CG25, a brain region involved in somatovisceral control, is speculated to play a role in depression. People with depression have abnormally high levels of activity in CG25.
See also 
- Mogilner A.Y., Benabid A.L., Rezai A.R. (2004). "Chronic Therapeutic Brain Stimulation: History, Current Clinical Indications, and Future Prospects". In Markov, Marko; Paul J. Rosch. Bioelectromagnetic medicine. New York, N.Y: Marcel Dekker. pp. 133–51. ISBN 0-8247-4700-3.
- McIntyre CC, Thakor NV (2002). "Uncovering the mechanisms of deep brain stimulation for Parkinson's disease through functional imaging, neural recording, and neural modeling". Crit Rev Biomed Eng 30 (4-6): 249–81. PMID 12739751.
- Machado A, Rezai AR, Kopell BH, Gross RE, Sharan AD, Benabid AL (June 2006). "Deep brain stimulation for Parkinson's disease: surgical technique and perioperative management". Mov. Disord. 21 (Suppl 14): S247–58. doi:10.1002/mds.2095910.1002/mds.20959. PMID 16810722.
- Diamond A, Shahed J, Azher S, Dat-Vuong K, Jankovic J (May 2006). "Globus pallidus deep brain stimulation in dystonia". Mov. Disord. 21 (5): 692–5. doi:10.1002/mds.20767. PMID 16342255.
- Richter E.O., Lozano A.M. (2004). "Deep Brain Stimulation for Parkinson's Disease in Movement Disorders". In Markov, Marko; Paul J. Rosch. Bioelectromagnetic medicine. New York, N.Y: Marcel Dekker. pp. 265–76. ISBN 0-8247-4700-3.