Depression is one of the most common and costly of all psychiatric disorders, afflicting more than 15 million Americans and 350 million people worldwide each year. Depression also frequently co-occurs with several physical health conditions that, together with the disorder itself, cause substantial morbidity and mortality. Identifying biobehavioral factors that can be targeted to prevent and treat depression is thus very important.
In a new review article published in the journal Psychological Bulletin, Dr. George Slavich and Dr. Michael Irwin describe the social, neural, physiologic, molecular, and genomic mechanisms that underlie depression and the many physical disease conditions that typically co-occur with this disorder. The review provides the basis for a social signal transduction theory of depression, which describes how social-environmental factors activate biological processes that lead to depression.
Central to this social signal transduction theory of depression is the hypothesis that experiences of social threat and adversity upregulate components of the immune system involved in inflammation. The key mediators of this response, called pro-inflammatory cytokines, can in turn elicit profound changes in behavior, which include the initiation of depressive symptoms such as sad mood, anhedonia, fatigue, psychomotor retardation, and social-behavioral withdrawal.
As described in the article, this highly conserved biological response to adversity is critical for survival during times of actual physical threat or injury. However, this response can also be activated by modern-day social, symbolic, or imagined threats, leading to an increasingly pro-inflammatory phenotype that may be a key phenomenon driving depression pathogenesis and recurrence, as well as the overlap of depression with several somatic conditions including asthma, rheumatoid arthritis, chronic pain, metabolic syndrome, cardiovascular disease, obesity, and neurodegeneration.
Insights from this theory may thus shed light on several important questions including how depression develops, why it frequently recurs, why it is strongly predicted by early life stress, and why it often co-occurs with symptoms of anxiety and with certain physical disease conditions.
“We have long known that depression can be highly recurrent, and that it frequently co-occurs with a number of other mental and physical health problems,” said Slavich. “Social signal transduction theory of depression attempts to explain this phenomenon by elucidating the social and biological processes that underlie this disorder.”
In the article, Slavich and Irwin say that the theory may also suggest new opportunities for preventing and treating depression by targeting inflammation.
Dr. George Slavich is an assistant professor and Society in Science – Branco Weiss Fellow in the Department of Psychiatry and Biobehavioral Sciences at UCLA. He is also a Research Scientist at the UCLA Cousins Center for Psychoneuroimmunology, where he directs the Laboratory for Stress Assessment and Research.
Dr. Michael Irwin is Cousins Professor of Psychiatry and Biobehavioral Sciences in the David Geffen School of Medicine at UCLA, Professor of Psychology in the UCLA College of Letters and Sciences, Director of the Cousins Center for Psychoneuroimmunology in the Semel Institute for Neuroscience and Human Behavior, and Director of the UCLA Mindful Awareness Research Center.
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