At their core, brain stimulation therapies are believed to work because the brain uses electrical activity to relay messages with itself. The way positively and negatively charged ions move through the walls of the brain cells allow for communication between neurons.
When an electrical signal in the brain reaches the end of a neuron (brain cell), the electrical activity causes the release of a neurotransmitter. A neurotransmitter is a small molecule that passes through the space between two neurons called a synapse, and relays a specific message to the other neuron. There are many different kinds of neurotransmitters, such as glutamate (excites neurons), GABA (inhibits neurons), dopamine (reward-driven learning), acetylcholine (works at the junction between muscles and nerves), and serotonin (important in maintaining mood), among many others.
In many of the brain stimulation therapies, the electrical activity will 'reset' the activity of the nerves, or cause the release of these neurotransmitters in the brain, although the exact mechanisms of many brain stimulation therapies are unknown.
ECT is considered for people with depression who have not had success with medication and psychotherapies. VNS is approved by the FDA as an adjunctive therapy for partial-onset epilepsy and treatment-resistant depression, although controversial because results of studies testing its effectiveness in treating major depression have been mixed. rTMS was approved for use by the FDA as a treatment for major depression for patients who have not responded to at least one antidepressant medication. It is also used in countries such as in Canada and Israel as a treatment for depression for patients who have not responded to medications and who might otherwise be considered for ECT. Deep brain stimulation (DBS) was first developed as a treatment for Parkinson's disease to reduce tremor, stiffness, walking problems and uncontrollable movements. So far, very little research has been conducted to test DBS for depression treatment, but the few studies that have been conducted show that the treatment may be promising.
Scientists are unsure how electroconvulsive therapy works to relieve depression, but it appears to produce many changes in the chemistry and functioning of the brain.
Vagus nerve stimulation was originally developed as a treatment for epilepsy. However, it became evident that it also had effects on mood, especially depressive symptoms. Using brain scans, scientists found that the device affected areas of the brain that are also involved in mood regulation. The pulses also appeared to alter certain neurotransmitters (brain chemicals) associated with mood, including serotonin, norepinephrine, GABA and glutamate.
Repetitive transcranial magnetic stimulation (rTMS) uses a magnet instead of an electrical current to activate the brain .An electromagnetic coil is held against the forehead near an area of the brain that is thought to be involved in mood regulation. Then, short electromagnetic pulses are administered through the coil. The magnetic pulse easily passes through the skull, and causes small electrical currents that stimulate nerve cells in the targeted brain region.
In deep brain stimulation (DBS), electrodes are surgically implanted in the brain, and electrical pulses are continuously delivered over the wires to the electrodes. it is unclear exactly how the device works to reduce depression or OCD, but scientists believe that the pulses help to "reset" the area of the brain that is malfunctioning so that it works normally again.
Pros for this therapy
Brain stimulation therapies are often last resorts, but they also have offered hope to many patients who are running out of effective options for treatment.
Cons for this therapy
Side effects are numerous for each therapy, and can vary in severity. The most common side effects associated with ECT are headache, upset stomach, and muscle aches. Some people may experience memory problems, especially of memories around the time of the treatment. People may also have trouble remembering information learned shortly after the procedure, but this difficulty usually disappears over the days and weeks following the end of an ECT course. It is possible that a person may have gaps in memory over the weeks during which he or she receives treatment. Side effects of VNS may include surgical complications such as infection from the implant surgery, or the device may come loose, move around or malfunction, which may require additional surgery to correct, voice changes or hoarseness, cough or sore throat, neck pain, discomfort or tingling in the area where the device is implanted, breathing problems, especially during exercise, and difficulty swallowing.
Side effects of rTMS may include discomfort at the site on the head where the magnet is placed. The muscles of the scalp, jaw or face may contract or tingle during the procedure. Mild headache or brief lightheadedness may result. It is also possible that the procedure could cause a seizure, although documented incidences of this are uncommon. A recent large-scale study on the safety of rTMS found that most side effects, such as headaches or scalp discomfort, were mild or moderate, and no seizures occurred. Because the treatment is new, however, long-term side effects are unknown. DBS carries risks associated with any type of brain surgery. For example, the procedure may lead to bleeding in the brain or stroke, infection, disorientation or confusion, unwanted mood changes, movement disorders, lightheadedness, trouble sleeping. Because the procedure is still experimental, other side effects that are not yet identified may be possible. Long-term benefits and side effects are unknown.
The history of brain stimulation with electrical means dates back to the early 19th century.
- Pierre Flourens and Luigi Rolando discovered that different parts of the brain do different things by studying lesions on pigeons and rabbits.
- Eduard Hitzig used electrical stimulation of dogs brains caused muscle contraction and discorvered the motor areas of the brain
- Robert Bartholow and Fedor Krause were some of the first to use electrical stimulation on human patients
- Victor Horsley invented stereotactic methods for brain surgery, which allowed precise location of brain structures
- Walter Rudolf Hess and Jose Delgado help invent chronic electrode implants, which allowed electrodes to dwell in the brains of animals such as cats and monkeys for study
- James Olds and others discovered brain stimulation reward, which showed that chemical or electrical stimulation of certain parts of the brain can be pleasurable
Specific brain stimulation therapies have become approved by the FDA in the latter half of the 20th century.
- Deep brain stimulation was approved for essential tremor in 1997, Parkinson's disease in 2002, and dystonia in 2003. It has been used experimentally for depression, obsessive-compulsive disorder, and chronic pain
- Electroconvulsive therapy has been used since the 1940's for treatment of several psychiatric disorders, but is now mostly used as a treatment for severe refractory depression, mania, and catatonia.
- Repetitive transcranial magnetic stimulation was first successfully used in 1985. Currently it can be used to treat depression, although the efficacy is debated. Investigational studies are ongoing for use with Parkinson's disease, migraines, and dystonia.
- Vagus nerve stimulation was approved for the treatment of epilepsy in 1997, and treatment resistant depression in 2005.
Brain stimulation therapies involve activating or touching the brain directly with electricity, magnets, or implants to treat depression and other disorders. Electroconvulsive therapy is the most researched stimulation therapy and has the longest history of use. Other stimulation therapies discussed here — vagus nerve stimulation, repetitive transcranial magnetic stimulation, magnetic seizure therapy, and deep brain stimulation—are newer, more experimental methods. Examples include electroconvulsive therapy, vagus nerve stimulation, repetitive transcranial magnetic stimulation, and deep brain stimulation.