Do depressed patients process pain abnormally?
Over 75% of patients with depression experience chronic pain and 30% to 60% of those who experience chronic pain also have symptoms of depression; however, despite the major overlapping of these two conditions very little is know about the nerobiological basis of how the brain processes pain among patients with major depressive disorder. A study reported in the November issue of Archives of General Psychiatry has shed new light on the subject, however. According to the study, patients with depression had decreased activity in areas of the brain responsible for pain modulation during painful heat stimulus. Conversely, these same patients experienced increased activity in the right anterior insular region, dorsal anterior cingulate, and right amygdala (emotion-processing areas of the brain) while anticipating pain. According to the researchers, “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… this mechanism could in part explain the high comorbidity of pain and depression when these conditions become chronic.” The following is an excerpt of an article from Medpage Today that reviews this fascinating study:
So they recruited 15 patients with major depressive disorder (12 females; mean age 24.5) and 15 healthy controls with no history of psychiatric disorders (10 females; mean age 24.3) to undergo functional magnetic resonance imaging before and during painful stimulation.
The depressed patients completed the Pain Catastrophizing Scale, which assesses magnification, rumination, and helplessness related to pain.
Both painful and non-painful levels of heat were applied to the participants’ forearms as they viewed images that signaled the intensity of heat to come.
The temperatures did not differ significantly between the groups; the painful stimulus was 115.5° F in the depressed patients and 116.4° F for the controls (P=0.08), and the non-painful stimulus was 102.2° F for both groups (P=0.59).
Both groups reported similar subjective ratings of the unpleasantness and intensity of the painful heat.
The depressed patients rated the non-painful heat as significantly more unpleasant (P=0.04), “a finding that is consistent with our previous observations of the increased affective bias in major depressive disorder at non-painful temperatures,” the researchers said.
During the anticipation of pain, the depressed patients had increased activation in the right anterior insular region, left anterior insular/inferior frontal gyrus, bilateral dorsal anterior cingulate cortex, right dorsolateral prefrontal cortex, several clusters in the left dorsolateral prefrontal cortex, clusters in the temporal and occipital lobes, and right amygdala.
The increased activity in the amygdala during anticipation was associated with greater levels of perceived helplessness toward pain (P=0.01) and rumination (P=0.02) in the depressed patients only.
During painful stimulation, the depressed patients had increased activity in the left parahippocampal gyrus and occipital cortex and the right amygdala, and decreased activity in the periaqueductal gray matter and the rostral anterior cingulate and prefrontal cortices.
The increased activity in the amygdala during painful stimulation was associated with perceived levels of helplessness (P=0.02) and rumination (P=0.03).
“These findings suggest that increased emotional reactivity during the anticipation of heat pain may lead to an impaired ability to modulate pain experience in major depressive disorder,” the researchers said.