Depression 'hijacks' brain circuits meant to help fight illness, study suggests
8 September 2009
Research from the Brighton and Sussex Medical School and University College London implies that the brain circuits that help us adapt our behaviour to best fight off an illness may be 'hijacked' during clinical depression.
Scientists have previously noted the similarity between symptoms of depression and our behaviour when ill. When sick, we often feel irritable or low in mood, and tend to be easily fatigued, lacking in appetite and energy or motivation to do things that we would normally enjoy.
In the new study, the researchers gave 16 men either a placebo injection or one with a typhoid vaccine - which causes the immune system to mount an inflammatory response similarly to when faced with an infection. A few hours later, the subjects undertook an emotional face processing task while their brains were scanned by fMRI.
Three hours after injection, those who received the typhoid vaccine reported a more negative mood. Those who received the placebo reported no significant mood change.
Furthermore, the fMRI scans showed that there was a change in brain activity during this period in a region known as the sub-genual cingulate, as well as other brain regions connected to it. Previous studies have implicated the sub-genual cingulate as having a key role in regulating mood and depression.
"This brain region shows strong connections to a number of other brain regions implicated in regulating reward, emotion and social processing," said Dr Neil Harrison from Brighton and Sussex Medical School, lead author on the study.
"It was striking that inflammation also regulated the mood-dependent connectivity between the sub-genual cingulate and each of these regions, suggesting that depression may be hijacking brain circuits associated with inflammation-associated mood change."
The researchers say this adds further evidence for the possible use of anti-inflammatory drugs in the treatment of depression.
"Currently only a small number of studies have looked at the role of anti-inflammatory drugs in the treatment of depression," said Dr Harrison. "However one such study using the anti-inflammatory drug celecoxib has shown an improvement in symptoms of depressed patients, our study suggests a potential mechanism for why this approach may be effective."
The researchers are planning studies in people with inflammatory disorders such as rheumatoid arthritis to see whether the same brain mechanisms underlie the beneficial effect of anti-inflammatory drugs on the depressive symptoms of these patients.
Image: Artist's illustration of depression. Credit: Adrian Cousins, Wellcome Images
Reference
Harrison NA et al. Inflammation causes mood changes through alterations in subgenual cingulate activity and mesolimbic connectivity. Biol Psychiatry 2009;66(5):407-14.