Electroshock, technically known as electroconvulsive therapy or ECT, is one of the most effective - and controversial - treatments for depression. Until recently, scientists have been at a loss to explain just how it works.

A new study from a team of researchers in Scotland published Monday in the Proceedings of the National Academy of Science suggests that ECT may reduce overactive communications between areas in the brain involved in thinking and areas associated with mood control.

In a nutshell, ECT is able to reduce the tension created by the impact of depression on thinking and concentration, Jennifer Perrin, a University of Aberdeen researcher and the study's lead author, said in an email interview.

Perrin and other researchers scanned the brains of nine severely depressed patients before and after they received ECT. The scans showed when different brain regions processed information simultaneously, suggesting how the areas are linked.

The researchers examined how more than 25,000 brain areas communicated and discovered that the strength of the connections between areas of the brain involved in thinking and areas involved in emotional processing decreased after ECT. The drop in connectivity strength was accompanied by a significant improvement in the patients' depressive symptoms, according to the study.

Given how effective ECT is, it's unfortunate that there's so little research available to understand how it works, said Irving Reti, associate professor of psychiatry at the Johns Hopkins University School of Medicine in Baltimore and the director of the brain stimulation program at the Johns Hopkins Hospital. Reti was unaffiliated with the study.

If we learn more about the pathways and the mechanisms involved, that in itself could lead to new treatments, he added.

When electroshock was introduced in the 1930s, psychiatrists figured the treatment worked by inducing fear or perhaps by causing patients to regress to an infantile mental state. As scientists began to examine the brain more closely, theories proliferated; scientists thought ECT worked by reducing blood flow to certain parts of the brain or by stimulating neuron growth.

ECT has fairly profound effects on brain function, according to Andrew Leuchter, a professor of psychiatry at the David Geffen School of Medicine at the University of California, Los Angeles. The process induces a generalized seizure that causes major disruptions to the normal patterns of blood flow and metabolism in the brain.

The treatment also changes the patterns of nerve cell firing, so it makes sense that ECT affects the connectivity between brain areas, Leuchter says.

The current finding lends support to a theory of depression called the hyperconnectivity hypothesis, which postulates that depressive minds have more functional links between brain regions than usual.

These links between brain regions still aren't fully understood, however.

We don't know whether this reduction in connection strength is a result of something like a neurotransmitter level changing, and further research will be necessary to clarify this, Perrin said.

The research points to a possible avenue for developing a less invasive treatment such as a drug - if scientists can figure out exactly how the connectivity is being tamped down.

One common side effect of ECT is memory loss, which researchers have tried to reduce by changing the placement of the electrodes on the patient's head, Perrin said.

The study, however, suggests ECT affects a region of the brain that is associated with both emotion and memory, making it difficult to separate the treatment from the side effect.

Brian McCabe, a neuroscientist at the University of Cambridge not involved in the study, said that the finding is interesting, but since the study involved only nine patients, it's only a start.

What's needed is to examine more subjects in order to sort out the extent of the associations seen by the Aberdeen researchers, McCabe said.