Scientists have discovered how electroconvulsive or electric shock therapy - a controversial but effective treatment - acts on the brains of severely depressed people and say the finding could help improve diagnosis and treatment of mental illness.
Electroconvulsive therapy (ECT) involves first anaesthetizing the patient and then electrically inducing a seizure.
It has a controversial reputation - gained in part because of its role in the 1975 film "One Flew Over The Cuckoo's Nest" starring Jack Nicholson - but is a potent and effective treatment for patients with mood disorders like severe depression.
Yet despite it being used successfully in clinical practice around the world for more than 70 years, scientists have until now not been entirely clear how or why it works.
Now a team from Aberdeen University in Scotland has shown for the first time that ECT affects the way different parts of the brain involved in depression communicate with each other.
In a study published in the Proceedings of the National Academy of Sciences (PNAS) journal they found ECT appears to turn down overactive connections between parts of the brain that control mood and parts that control thinking and concentrating.
This stops the overwhelming impact that depression has on patients' ability to enjoy life and carry out day-to-day activities, they said.Alpha Stim
"We've solved a 70-year-old therapeutic riddle," said Ian Reid, a professor of psychiatry at the University of Aberdeen who led the study.
"Our key finding is that if you compare the connections in the brain before and after ECT, ECT reduces the connection strength," he said in a statement.
"For the first time we can point to something that ECT does in the brain that makes sense in the context of what we think is wrong in people who are depressed."
In recent years, experts have developed a new theory on how depression affects the brain that suggests there is a "hyperconnection" between the areas of the brain involved in emotional processing and mood change and the parts of the brain involved in thinking and concentrating.