CHICAGO–People with clinical depression may be unable to "snap out of it" because of faulty wiring in the brain, a new study shows.
Researchers who compared the way people with severe depression responded to negative stimuli relative to a group of healthy controls found that the circuits involved in controlling emotions were disrupted in the depressed people.
"The neural circuits involved with regulating emotions may be damaged in people with this condition," says the lead author of the study, neuroscientist Tom Johnstone, of the University of Wisconsin-Madison's School of Medicine and Public Health.
The study, published yesterday in the journal Neuroscience, shows one of the hallmarks of depression is that people with the condition seem to be unable to pull themselves out of a funk or black mood.
In order to figure out what goes awry in these situations, Johnstone and his colleagues conducted an experiment on a group of 21 depressed people and 18 healthy controls.
Researchers tried to manipulate them into a negative state of mind and then watched how well they could bounce back.
Specifically, they presented their guinea pigs with a series of images of things such as car accidents or threatening-looking animals and then asked them to consciously modulate their responses, by envisioning more positive outcomes than the one implied.
They also asked the participants to try imagining the situation was acted out rather than real.
"We ask them to reframe the content of what they're seeing," says Johnstone. "We hope to engage cognitive areas in re-interpreting the emotional content of a stimulus."
As expected, all of the individuals had increased brain activity in the prefrontal cortical areas that are known to regulate the emotional parts of the brain.
In the healthy individuals, high levels of prefrontal cortical activity correlated with low levels of activity in the amygdala, the almond-shaped structure that appears to regulate fear and anxiety.
In other words, they were able to quell their emotional response to the images.
In the depressed people, high levels of activity in the amygdala persisted in spite of the intense activity in the regulatory regions, and even increased in response to it, suggesting that their conscious effort to control their emotions was thwarted by dysfunctional brain circuits.
The researchers speculated that signals from the prefrontal cortical area of the brain are not getting through to the amygdala in the depressed people. But the reasons are still unknown.
The findings suggest that cognitive behavioural therapies based on a belief that someone can change the way they feel about a situation by altering the way they think about it may be counterproductive for some people.
"Our results suggest that there is a subgroup of patients with depression for whom traditional cognitive therapy may be contra-indicated," says senior author Richard Davidson. He notes that in some cases, the depressed person's effort to recalibrate their response resulted only in greater emotional activity.