Brain Less Responsive During Depression, But Can Recover

Researchers measured the brain's responsiveness using magnetic stimulation over the brain and targeted muscle movement. "Our results show that the brain's responsiveness or 'excitability' after exercise is different in healthy people compared with those who are depressed," said study author Klaus Ebmeier, MD, with the University of Edinburgh and Royal Edinburgh Hospital, United Kingdom. "Furthermore, the responsiveness or excitability returns to more healthy levels in recovered depressed people. This supports the notion that reduced brain excitability in depression is a reversible state."

Depression is a disabling medical illness involving disruptions in brain functions. A combination of symptoms -- including changes in patterns of mood or emotion typically characterized by periods of despair, low self-esteem, apathy, withdrawal and guilt -- interfere with the ability to work, sleep, eat and enjoy once pleasurable activities. Depression affects over 17 million Americans each year and the World Health Organization estimates that by the beginning of the next century, major depression will be one of the most important causes of ill health overall.

Using Transcranial Magnetic Stimulation (TMS), the brain is stimulated with an insulated electromagnetic coil held close to the surface of the head. "If the stimulation is strong enough over the motor area of the brain, it will produce a muscle movement, for example a thumb twitch," said Ebmeier. This muscle movement can be recorded with an electrode over the muscle. A muscle targeted with stimulation will twitch more after exercising it than after rest. "Thus TMS can measure the brain's excitability in that it measures the brain's responsiveness to a defined stimulus," Ebmeier said. TMS used in this form is non-invasive, painless and safe.

The study included 10 healthy volunteers with no psychiatric history, 10 currently depressed patients and 10 patients who had recovered from depression within the previous 6 months. All depressed and recovered patients were on antidepressant medication, so the differences in response rates were likely not due to drugs, Ebmeier said.

In addition to stimulation of the brain, the researchers measured study participants' reaction times using computer-generated tasks, and motor speed by measuring how fast they could tap on a keyboard. Compared with the healthy volunteers, the depressed patients showed significant impairment.

"The group that had recovered from a depressive episode within the last six months showed improvement in these reaction time and tapping tests, but they still did not reach the performance levels of healthy volunteers," said Ebmeier. "However, the muscle responses to Transcranial Magnetic Stimulation after exercise showed almost complete recovery in this group. This suggests that these muscle responses may be a more sensitive way of measuring recovery from a depressed state than the neuropsychological tests often performed."

Research using magnetic stimulation as a treatment for depression is currently being conducted. "Here we have an objective measure that suggests the brains of depressed patients do not function normally," said Ebmeier. "We have TMS as an investigative tool, which may enable us to expand our knowledge about how the brain works in depression, and possibly how it may work as an antidepressant treatment by reversing the effects of depression."

The American Academy of Neurology, an association of more than 16,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research.