Through functional MRI (fMRI), the brains of individuals with major depressive disorder appear to react more strongly when anticipating pain and also display altered functioning of the neural network that modifies pain sensitivity, according to a report in the November issue of the Archives of General Psychiatry.
Irina A. Strigo, PhD, of the University of California San Diego, La Jolla, and colleagues studied 15 young adults with major depressive disorder (average age 24.5) who were not taking medication, and 15 individuals who were the same age (average 24.3 years) and had the same education level, but did not have depression. Patients with depression completed a questionnaire that evaluated their tendencies to magnify, ruminate over or feel helpless in the face of pain.
All participants underwent fMRI while their arms were exposed to a thermal device heated to painful levels (an average of 115 F to 116 F) and also to non-painful temperatures. Visual cues were presented before the heat was applied.
Compared with the controls, in patients with depression, brain activity increased, including in the right amygdale, in anticipation of painful stimuli. They also displayed increased activity in the right amygdala and decreased activity in other areas, including those responsible for pain modulation (adjusting sensitivity to pain), during the painful experience.
To examine whether the activation of the amygdala was associated with passive coping styles, the researchers compared the percentage change in the activations of the amygdala with the helplessness, rumination and ramification reported by the participants with depression.
Significant positive correlations were observed in the major depressive disorder group between greater helplessness scores and greater activity in the right amygdala during the anticipation of pain, according to the authors.
“The anticipatory brain response may indicate hypervigilance to impending threat, which may lead to increased helplessness and maladaptative modulation during the experience of heat pain. This mechanism could in part explain the high comorbidity of pain and depression when these conditions become chronic,” the authors wrote.
The Barrow Neurological Foundation, grants from the National Institute of Mental Health, the National Association for Research in Schizophrenia and Depression and the University of California San Diego Center of Excellence for Stress and Mental Health supported the study.