Medical procedure in which electrical current is passed through the brain
Electroconvulsive therapy (ECT) or electroshock therapy (EST) is a psychiatric treatment during which a generalized seizure (without muscular convulsions) is electrically induced to manage refractory mental disorders. Typically, 70 to 120 volts are applied externally to the patient's head, resulting in approximately 800 milliamperes of direct current passing between the electrodes, for a duration of 100 milliseconds to 6 seconds, either from temple to temple (bilateral ECT) or from front to back of one side of the head (unilateral ECT). However, only about 1% of the electrical current crosses the bony skull into the brain because skull impedance is about 100 times higher than skin impedance.
Aside from effects on the brain, the general physical risks of ECT are similar to those of brief general anesthesia. Immediately following treatment, the most common adverse effects are confusion and transient memory loss. Among treatments for severely depressed pregnant women, ECT is one of the least harmful to the fetus.
ECT is often used as an intervention for major depressive disorder, mania, autism, and catatonia. The usual course of ECT involves multiple administrations, typically given two or three times per week until the patient no longer has symptoms. ECT is administered under anesthesia with a muscle relaxant. ECT can differ in its application in three ways: electrode placement, treatment frequency, and the electrical waveform of the stimulus. These treatment parameters can pose significant differences in both adverse side effects and symptom remission in the treated patient.
Placement can be bilateral, where the electric current is passed from one side of the brain to the other, or unilateral, in which the current is solely passed across one hemisphere of the brain. High-dose unilateral ECT has some cognitive advantages compared to moderate-dose bilateral ECT while showing no difference in antidepressant efficacy.
History.
As early as the 16th century, agents to induce seizures were used to treat psychiatric conditions. In 1785, the therapeutic use of seizure induction was documented in the "London Medical and Surgical Journal". As to its earliest antecedents one doctor claims 1744 as the dawn of electricity's therapeutic use, as documented in the first issue of "Electricity and Medicine". Treatment and cure of hysterical blindness was documented eleven years later. Benjamin Franklin wrote that an electrostatic machine cured "a woman of hysterical fits." By 1801, James Lind as well as Giovanni Aldini had used galvanism to treat patients with various mental disorders. G.B.C. Duchenne, the mid-19th century "Father of Electrotherapy", said its use was integral to a neurological practice.
In the second half of the 19th century, such efforts were frequent enough in British asylums as to make it notable.
Convulsive therapy was introduced in 1934 by Hungarian neuropsychiatrist Ladislas J. Meduna who, believing mistakenly that schizophrenia and epilepsy were antagonistic disorders, induced seizures first with camphor and then metrazol (cardiazol). Meduna is thought to be the father of convulsive therapy. 
In 1937, the first international meeting on schizophrenia and convulsive therapy was held in Switzerland by the Swiss psychiatrist Max Müller. The proceedings were published in the "American Journal of Psychiatry" and, within three years, cardiazol convulsive therapy was being used worldwide. 
The ECT procedure was first conducted in 1938 by Italian neuro-psychiatrist Ugo Cerletti and rapidly replaced less safe and effective forms of biological treatments in use at the time. Cerletti, who had been using electric shocks to produce seizures in animal experiments, and his assistant Lucio Bini at Sapienza University of Rome developed the idea of using electricity as a substitute for metrazol in convulsive therapy and, in 1938, experimented for the first time on a person affected by delusions. 
It was believed early on that inducing convulsions aided in helping those with severe schizophrenia but later found to be most useful with affective disorders such as depression. Cerletti had noted a shock to the head produced convulsions in dogs. The idea to use electroshock on humans came to Cerletti when he saw how pigs were given an electric shock before being butchered to put them in an anesthetized state. Cerletti and Bini practiced until they felt they had the right parameters needed to have a successful human trial. Once they started trials on patients, they found that after 10–20 treatments the results were significant. Patients had much improved. 
A positive side effect to the treatment was retrograde amnesia. It was because of this side effect that patients could not remember the treatments and had no ill feelings toward it. 
ECT soon replaced metrazol therapy all over the world because it was cheaper, less frightening and more convenient. Cerletti and Bini were nominated for a Nobel Prize but did not receive one. By 1940, the procedure was introduced to both England and the US. In Germany and Austria, it was promoted by Friedrich Meggendorfer. Through the 1940s and 1950s, the use of ECT became widespread. At the time the ECT device was patented and commercialized abroad, the two Italian inventors had competitive tensions that damaged their relationship. In the 1960s, despite a climate of condemnation, the original Cerletti-Bini ECT apparatus prototype was contended by scientific museums between Italy and the US. The ECT apparatus prototype is now owned and displayed by the Sapienza in Rome.
In the early 1940s, in an attempt to reduce the memory disturbance and confusion associated with treatment, two modifications were introduced: the use of unilateral electrode placement and the replacement of sinusoidal current with brief pulse. It took many years for brief-pulse equipment to be widely adopted. 
In the 1940s and early 1950s, ECT was usually given in an "unmodified" form, without muscle relaxants, and the seizure resulted in a full-scale convulsion. A rare but serious complication of unmodified ECT was fracture or dislocation of the long bones. In the 1940s, psychiatrists began to experiment with curare, the muscle-paralysing South American poison, in order to modify the convulsions. The introduction of suxamethonium (succinylcholine), a safer synthetic alternative to curare, in 1951 led to the more widespread use of "modified" ECT. A short-acting anesthetic was usually given in addition to the muscle relaxant in order to spare patients the terrifying feeling of suffocation that can be experienced with muscle relaxants.
The steady growth of antidepressant use along with negative depictions of ECT in the mass media led to a marked decline in the use of ECT during the 1950s to the 1970s. The Surgeon General stated there were problems with electroshock therapy in the initial years before anesthesia was routinely given, and that "these now-antiquated practices contributed to the negative portrayal of ECT in the popular media." "The New York Times" described the public's negative perception of ECT as being caused mainly by one movie: "For Big Nurse in "One Flew Over the Cuckoo's Nest," it was a tool of terror, and, in the public mind, "shock therapy" has retained the tarnished image given it by Ken Kesey's novel: dangerous, inhumane and overused".
In 1976, Dr. Blatchley demonstrated the effectiveness of his constant current, brief pulse device ECT. This device eventually largely replaced earlier devices because of the reduction in cognitive side effects, although as of 2012 some ECT clinics still were using sine-wave devices. 
The 1970s saw the publication of the first American Psychiatric Association (APA) task force report on electroconvulsive therapy (to be followed by further reports in 1990 and 2001). The report endorsed the use of ECT in the treatment of depression. The decade also saw criticism of ECT. Specifically, critics pointed to shortcomings such as noted side effects, the procedure being used as a form of abuse, and uneven application of ECT. The use of ECT declined until the 1980s, "when use began to increase amid growing awareness of its benefits and cost-effectiveness for treating severe depression". In 1985, the National Institute of Mental Health and National Institutes of Health convened a consensus development conference on ECT and concluded that, while ECT was the most controversial treatment in psychiatry and had significant side-effects, it had been shown to be effective for a narrow range of severe psychiatric disorders.
Because of the backlash noted previously, national institutions reviewed past practices and set new standards. In 1978, the American Psychiatric Association released its first task force report in which new standards for consent were introduced and the use of unilateral electrode placement was recommended. The 1985 NIMH Consensus Conference confirmed the therapeutic role of ECT in certain circumstances. The American Psychiatric Association released its second task force report in 1990 where specific details on the delivery, education, and training of ECT were documented. Finally, in 2001 the American Psychiatric Association released its latest task force report. This report emphasizes the importance of informed consent, and the expanded role that the procedure has in modern medicine. By 2017, ECT was routinely covered by insurance companies for providing the "biggest bang for the buck" for otherwise intractable cases of severe mental illness, was receiving favorable media coverage, and was being provided in regional medical centers.
Though ECT use declined with the advent of modern antidepressants, there has been a resurgence of ECT with new modern technologies and techniques. Modern shock voltage is given for a shorter duration of 0.5 milliseconds where conventional brief pulse is 1.5 milliseconds.
In a review from 2022 of neuroimaging studies based on a global data collaboration ECT was suggested to work via a temporary disruption of neural circuits followed by augmented neuroplasticity and rewiring.
Modern use.
ECT is used, where possible, with informed consent in treatment-resistant major depressive disorder, bipolar depression, treatment-resistant catatonia, prolonged or severe mania, and in conditions where "there is a need for rapid, definitive response because of the severity of a psychiatric or medical condition (e.g., when illness is characterized by suicidality, psychosis, stupor, marked psychomotor retardation, depressive delusions or hallucinations, or life-threatening physical exhaustion associated with mania)." It has also been used to treat autism in adults with an intellectual disability, yet findings from a systematic review found this an unestablished intervention.
Major depressive disorder.
For major depressive disorder, despite a Canadian guideline and some experts arguing for using ECT as a first line treatment, ECT is generally used only when one or other treatments have failed, or in emergencies, such as imminent suicide. ECT has also been used in selected cases of depression occurring in the setting of multiple sclerosis, Parkinson's disease, Huntington's chorea, developmental delay, brain arteriovenous malformations, and hydrocephalus.
Efficacy.
A meta-analysis on the effectiveness of ECT in unipolar and bipolar depression indicated that although patients with unipolar depression and bipolar depression responded to other medical treatments very differently, both groups responded equally well to ECT. Overall remission rate for patients given a round of ECT treatment was 50.9% for those with unipolar depression and 53.2% for those with bipolar depression. Most severely depressed patients respond to ECT.
In 2004, a meta-analysis found in terms of efficacy, "a significant superiority of ECT in all comparisons: ECT versus simulated ECT, ECT versus placebo, ECT versus antidepressants in general, ECT versus tricyclics and ECT versus monoamine oxidase inhibitors."
In 2003, The UK ECT Review Group published a systematic review and meta-analysis comparing ECT to placebo and antidepressant drugs. This meta-analysis demonstrated a large effect size (high efficacy relative to the mean in terms of the standard deviation) for ECT versus placebo, and versus antidepressant drugs.
Compared with repetitive transcranial magnetic stimulation (rTMS) for people with treatment-resistant major depressive disorder, ECT relieves depression as shown by reducing the score on the Hamilton Rating Scale for Depression by about 15 points, while rTMS reduced it by 9 points.
Other estimates regarding the response rate in treatment resistant depression vary between 60–80%, with a remission rate of 50–60%. In addition to reducing symptoms of depression and inducing relapse, ECT has also been shown to reduce the risk of suicide, improve functional outcomes and quality of life as well as reduce the risk of re-hospitalization. Efficacy does not depend on depression subtype. With regards to treatment resistant schizophrenia, the response rate is 40–70%.
Follow-up.
There is little agreement on the most appropriate follow-up to ECT for people with major depressive disorder. The initial course of ECT is then transitioned to maintenance ECT, pharmacotherapy or both. When ECT is stopped abruptly, without a bridge to maintenance ECT or medications (usually antidepressants and Lithium), it is associated with a relapse rate of 84%. There is no defined schedule for maintenance ECT, however it is