November 6, 2008

DR MUIRIS HOUSTON, Medical Correspondent

THE BRAINS of people with depression react more strongly when anticipating pain and also show altered function in the part of the brain that controls pain sensitivity compared with people without depression, research published this morning suggests.

Doctors at the University of California in San Diego, in the United States, carried out brain scans on two groups of young adults.

Some 15 people with an average age of 24.5 years with major depressive disorder were compared with a small group of similar age and educational attainment who did not have depression.

Both groups underwent functional MRI scanning while their arms were exposed to painful levels of heat.

Visual cues were used to signal the imminent application of heat.

Patients with depression also completed a questionnaire designed to assess their tendencies to magnify, ruminate over or feel helpless in the face of pain.

Compared with the control group, patients who suffered from depression showed increased activation in a part of the brain known as the right amygdala during the anticipation of painful stimuli.

This part of the brain also "lit up" during the painful experience, and other parts of the brain responsible for adjusting pain sensitivity showed reduced activation, according to the researchers.

The researchers also found a link between greater helplessness scores and greater activity in the right amygdala in those participants who suffered from depression.

"The anticipatory brain response may indicate hypervigilance to impending threat, which may lead to increased helplessness and maladaptive modulation during the experience of heat pain," the authors said.

"This mechanism could in part explain the high co-morbidity of pain and depression when these conditions become chronic."

It is known that chronic pain occurs in about 75 per cent of patients with depression, while 30-60 per cent of patients with chronic pain experience symptoms of depression.

But Dr Irina Striga and her colleagues emphasised that their findings were based on a relatively small sample and called for further more extensive research to be carried out before any generalisation could be made.

© 2008 The Irish Times