Scientists have tried to explain in a new study why people who suffer from depression in later life are harder to treat and keep well in the long term.
The study led by Toronto's Baycrest has found that older adults with depression don't respond normally to emotional stimuli, such as when they see happy, sad or neutral faces.
The study appears online this week in the American Journal of Geriatric Psychiatry.
"In our study we found significant differences between older depressed subjects and older healthy subjects in how they emotionally respond to and perceive facial expressions," said principal investigator Dr. Linda Mah, a clinician-scientist in the Mood Clinic at Baycrest.
Emotion dysregulation is already well established in mid-life depression and some studies have shown it to be predictive of a relapse of mood symptoms. But the majority of late-life depression studies have concentrated on the link with cognitive decline, suggesting that the more impaired the cognitive functions the greater the chances of a poor prognosis in depression.
"Our data suggest that we need to also focus on emotion to better understand the neurobiology of late-life depression, so we can treat it more effectively and help people feel better longer," said Dr. Mah.
In the study, 11 un-medicated outpatients with major depressive disorder, and 11 healthy comparison subjects, participated in two tasks that involved looking at photographs of faces with happy, sad, fearful or neutral expressions. The age range of participants was 60 to 87.
In the first task, participants were asked to make judgments regarding a physical feature of faces, rather than judging the emotional expression. In the second task, participants were asked to label the emotional expressions on faces.
The study found that healthy controls were 16 percent slower in making judgments about physical features of the faces with positive or negative emotional expressions (happy, sad, fearful) relative to neutral faces - an indication that they were distracted or affected by the emotional expressions on faces.
The depressed participants showed no differences in response time to rating physical aspects of faces with emotional expressions or neutral faces. This suggests they were less sensitive to the effects of positive or negative emotional expressions.
In the second task, depressed participants had greater than 60 percent more difficulty with correctly labeling neutral faces, compared to healthy subjects. Depressed participants misread neutral expressions as happy, sad or fearful.
Dr. Mah noted that an impaired ability to read other people's emotional expressions can have social consequences and affect the quality of social interactions with others.
She also pointed out that these abnormalities in emotional processing seen in older depressed adults are distinct from those already reported in younger depressed adults who tend to perceive nd process emotional stimuli more negatively overall when compared to healthy subjects.