Given that many readers found my claims about the nature of depression controversial (here and here), I thought I would share a somewhat longer articulation of my approach to conceptualizing depression called the Behavioral Shutdown Model. This formulation is an extension of the unified theory of psychology and is adopted from an earlier paper I wrote on this topic.
Consider a television commercial that begins with an attractive woman isolating herself at a party. Everyone else appears to be having a good time, yet she stands in the background, ostensibly gripped in the throes of a seemingly inexplicable sadness. The cultural milieu is of upper middle class suburbia.
A soft voice inquires and informs, “Have you experienced periods of depressed mood? Have you lost interest in things you used to enjoy? Do you feel tired, guilty, ineffective or hopeless? Depression is an illness. Ask your doctor about new antidepressant treatments available.” The implicit message of the commercial is clear. When people are suffering from depression, something has gone wrong with the physiology of the brain.
Now imagine a different commercial. This one begins with an impoverished woman getting slapped by her husband. Her three children are having difficulties in school. Her husband controls her, and she has little in the way of social support. She recently immigrated to the United States and cannot get a job because she only speaks a little English. She frequently faces prejudice and racism.
Now imagine a voice overlay that asks, “Have you been feeling down or depressed, guilty or hopeless? Have you lost interest in things you usually enjoy? Depression is an illness. Ask your doctor about new antidepressant treatments available.” Somehow the “depression as disease” message in this commercial is less convincing.
As these two vignettes illustrate, different portrayals can lead to radically different notions regarding the nature of depression. Yet, how depression is conceptualized is critically important. Depression is a major public health issue, and the theoretical paradigms that guide our understanding of the condition influence public opinion, health policies, treatment strategies, and research.
Although terms like "depression" are used all the time in normal conversation, clinically speaking, a Major Depressive Episode (MDE) is defined by the Diagnostic and Statistical Manual of Mental Disorders as the presence of 5 out of 9 nine psychological and behavioral symptoms (depressed mood, anhedonia, agitation or retardation, fatigue or low energy, feelings of worthlessness or guilt, thoughts of death, change in appetite/weight, sleeping difficulties, and diminished ability to concentrate) present most every day for a period of two weeks.
The prevailing model in psychiatry is that MDD is a disease of the brain. There are some good reasons for this position. In addition to the fact that depressive disorders are associated with difficulties in psychosocial functioning and higher mortality rates, neuroimaging studies have shown differences in the activity of the prefrontal cortex, the basal ganglia, the amygdala-hippocampus complex, and the thalamus in the brains of depressed individuals. Differences in the neuro-endocrine systems of depressed individuals have also been well documented. Additionally, Selective Serotonin Reuptake Inhibitors (SSRIs) and related anti-depressants can be effective treatments for reducing depressive symptoms.
And yet, despite these important findings, neurophysiological causal models of depression remain elusive. Although there are some promising avenues, no biological malfunction theory has much current credibility and the popular “chemical imbalance” theory of depression is now seen by most scholars as a failed hypothesis that remains alive only because of the power of marketing (see here, here, here and here).
One possible reason for the lack of progress is how depression is being conceptualized by modern psychiatry. The Behavioral Shutdown Model (BSM) explored here suggests an alternative interpretation of MDD and depression in general. Rather than viewing MDD as the consequence of a neurophysiological dysfunction, the BSM suggests that depression is actually an evolved defensive strategy.
The distinction between biological dysfunction and a defense strategy is an important one. A biological dysfunction is the failure of an organ or system to function in accord with its evolved design. A heart attack is an example of a dysfunction because the heart was fashioned via evolutionary processes to circulate blood throughout the body. Broken bones, cancers, and strokes are also examples of dysfunctions.
A defensive strategy, on the other hand, is an evolved method for signaling and/or reacting to a problem. When the influenza virus infects the human body, a number of different things happen, some of which are manifestations of defects and some of which are defenses.
Internally, the virus infects and transforms the human cells for its own reproductive benefit, causing clear defects. Symptoms include fever, coughing, and feeling achy, tired, and rundown. It used to be believed the coughing and fever were caused by the virus and were manifestations of cellular defects. Yet, the fever and coughing are in fact evolved defenses.
The increase in body temperature, for example, hinders the speed and effectiveness with which the virus can reproduce. Identifying a symptom as a defense strategy rather than a manifestation of a defect is important because it leads to a different intervention strategy. For example, medications given to reduce fever (once presumed to be part of the defect) actually prolong the duration of the flu virus in the body.
But how might depression be a defensive strategy? On the surface, the depressed mood, decreased energy, loss of interest in pleasurable activities, and change in sleep patterns associated with depression appear quite dysfunctional.
To understand how depression might be functional in an evolutionary sense, it is useful to first consider the evolutionary significance of pain. To effectively solve problems in its environment, an organism must have mechanisms that allow it to approach situations that are beneficial and avoid situations that are harmful. Pleasure can be thought of as the signal to approach and pain the signal to avoid. Although pain is almost always unwanted, the capacity to experience physical pain is immensely important. Physical pain signals something is wrong with the structural integrity of the body. Broken bones, lacerations, torn ligaments, ulcers etc., put the organism at risk or hinder its capacity to function and pain signals the presence of the problem. Pain also motivates the organism to avoid whatever is causing the difficulty and helps the organism to learn to avoid it in the future.
Evolutionarily informed theorists now recognize that emotional pain serves a very important function, similar to that of physical pain. Whereas physical pain signals problems with the structural integrity of the body, emotional pain signals problems with how the individual is interacting with some aspect of his or her environment, usually the social environment. We feel emotional pain when we fail to achieve, when a loved one dies, or when we are criticized, rejected, or controlled because these types of events involve loss of important resources in the social environment such as status, solidarity, or autonomy.
There are many different types of emotional pain because there are different types of problems in the social environment that one must avoid. Disappointment, sadness, and grief signal one has incurred losses or failures. Fear and anxiety signal emotional or physical pain might occur in the future. Shame signals loss of status and functions to avoid conflicts and submit to more powerful others. Anger is activated to defend oneself from others’ control or, conversely, to punish others for insubordination or betrayal. Guilt involves making reparations for selfish behavior to avoid the problem of retaliation.
In short, negative emotions are evolved strategies that allow for the identification and avoidance of potential problems, particularly in the social domain. As such, the presence of intense negative emotion is not necessarily indicative of a biological dysfunction. This is important because, as evidenced by the symptom list in the DSM, there is significant overlap between intense negative affect for a period of two weeks or more and a diagnosis of MDD.
To explore the possibility that depression is an evolved defensive strategy, it is useful to consider behavior in terms of evolutionary theory. From a Darwinian perspective, behavior can be thought of as the process of expending energy or working in order to control and structure the environment in a way that allows for survival and reproductive success. Control of larger territories, access to better food, higher social status, etc. is obviously advantageous. However, the behavioral investment needed to acquire and maintain these resources is expensive. It costs energy both in terms of basic calories and in terms of increasing risk of injury and loss. Resources might be frequently not available, which can make behavioral investments are fruitless. Additionally, competition over valuable resources can be fierce, often resulting in injury. This analysis gives rise to a cost-to-benefit ratio of behavioral investment, a ratio much like that in economics.
But what does this model have to do with depression? The cost-to-benefit ratio suggests that organisms can maximize the ratio by increasing benefits or by decreasing costs. Increasing benefits is associated with actively acquiring some resource (food, sex, status) in the environment via behavioral investment. The individual’s state of actively working to increase benefit can be described as desire. Decreasing behavioral investment can also be a way in which organisms deal with the cost-to-benefit ratio. There are many examples of behavioral shutdown mechanisms in nature, such as sleep, hibernation, and exhaustion, that function to decrease behavioral expenditure and conserve energy.
Broadly speaking, behavioral shutdown should result if an organism is getting a poor return (i.e., high costs, little benefit) from its behavioral investment. That is, if an organism is expending 8 behavioral units and only getting back 4 units, that is a bad ratio. If it tries everything in its behavioral repertoire, yet the ratio remains the same, a "best in a bad situation" solution is to decrease the amount of the behavioral investment in an effort to reduce net loss. It is better to expend 2 and get back 1 over the same period of time than the 8:4 ratio previously obtained.
This understanding gives rise to the Behavioral Shutdown Model (BSM), which suggests that depression may represent an evolved tendency to decrease behavioral expenditure in response to chronic danger, stress, or consistent failure to achieve one’s goals.
The BSM offers a potential explanation for many features of depression. For example, it strongly predicts that depression should be more likely to occur in situations that are chronically dangerous, humiliating, or repeatedly result in failure to achieve one’s goals. These are circumstances in which the cost-to-benefit ratio is the worst and therefore the most effective strategy is to reduce costs.
Consistent with this prediction, situations in which the individual feels chronically trapped or humiliated are most likely to produce symptoms of depression. To give just one example, almost 50 percent of battered women are depressed. There is also strong evidence that the onset of many Major Depressive Episodes are preceded by major stressful life events. Also consistent with the BSM, rates of MDD vary with socioeconomic status. Those individuals in the lowest quartile of socioeconomic status are almost twice as likely to be depressed compared with those in the highest quartile.
In addition to offering an explanation as to why certain situations are more likely to result in depression, the BSM also explains many of the symptoms of depression. The model explains why emotional pain is such a prominent feature of depression, as the pain is a signal that things are not going well.
Additionally, behavioral shutdown is the antithesis of active behavioral investment and thus the BSM explains why anhedonia is such a fundamental characteristic of depressive conditions. It also directly accounts for why low energy is such a prominent complaint.
The model also explains why negative cognitions are so prominent in depression. Cognitive theorists have clearly documented how depressed individuals are hypersensitive to any indications of loss, failure, or rejection. In direct accordance with the BSM, recent cognitive models have conceptualized depressed individuals as investors with few resources who take risk-aversive strategies to avoid loss. In short, the BSM offers a potential explanation for many of the symptoms of depression.
The BSM also provides explanations for findings that are difficult to explain from a disease model perspective. Because so many different things can result in difficulties in solving important problems, the BSM model accounts for why so many different causal pathways result in depression. Behavioral shutdown should be a matter of degree, thus the BSM also accounts for why symptoms of depression exist on a continuum that range from chronic, severe depressions to minor depressions to adjustment disorders to low mood.
Since the model suggests depression should be associated with difficulties in functioning, the BSM explains why depressive symptoms evidence such a high comorbidity with other mental disorders.
Finally, because it is an evolutionary model, the BSM also readily accounts for the fact that there is a substantial genetic component associated with depression.
The BSM is valuable in that it links the causes (triggers) with the effects (symptoms) of depression in a logical sequence. It also bears the hallmarks of a good hypothesis because it is parsimonious, consistent across disciplines (from physics to the human social sciences), and makes clear predictions.
To give just a few examples, the model predicts that because depressed individuals are focused on avoiding further loss, they should perceive more negative and pessimistic outcomes. Depressed individuals should also be risk aversive and tend to avoid potentially threatening stimuli. Likewise, depressed individuals should be hypersensitive to loss, failure or rejection. Because depressed individuals should be inclined to give up when faced with difficulty, such individuals should demonstrate a very low tolerance for frustration. Also, depressed individuals should exhibit diminished curiosity and explorative tendencies and should shun uncertainty, novelty, and sensation seeking. They should be very averse to conflict, particularly with others who are of equal or higher status. They should also engage in less social exchange. Depressed individuals should also demonstrate a decrease in behavioral activity. In short, the BSM makes many clear, easily testable predictions about both the triggers and symptoms associated with depressive condition.
It is important to note that considering depression as a state of shutdown that emerges from the basic design of the neurobehavioral investment system does not mean that MDD is not a serious health condition. Anyone who has had depression or who has worked with depressed individuals knows how painful, distressing, and difficult depression can be.
While the BSM should not diminish the seriousness of depression as a condition, it should serve to orient both patients and treating professionals to think about the condition anew. It raises the question of what might be shutting the individual down? In what ways does the individual feel their power has been removed or blocked? In what ways might they not be getting their core needs for relational value and social influence met? In what ways might the individual be having problems in processing their emotions? In what ways might they have experienced trauma that is blocking their growth? These are, of course, the kinds of questions that many therapists ask when working with someone who is depressed. The BSM provides a clear framework for linking these issues with the symptoms of the syndrome. And the basic idea is that some kind of emotional, relational, cognitive work needs to be done, as well as re-aligning the habits and lifestyles that engage the behavioral activation system and lead to psychological nourishment.
The Behavioral Shutdown Model highlights how it is possible to view depression as an evolved defense and, in so doing, challenges the dominant medical model. The BSM has significant health policy implications. The BSM argues for a fairly radical shift in how depression is conceptualized by clinicians, theorists, and researchers.
The BSM suggests that depression may be to mental health what pain is to physical health. One could imagine the conceptual confusion if the medical profession at large viewed pain as a disease. Although sometimes this might be a valid conception (as in some cases of chronic pain), for the most part viewing pain as a disease as opposed to a symptom would be highly problematic. Such a paradigm would lead to significant confusion about cause and effect. This would be particularly true if no assessment of structural damage to the body was made. Yet, the BSM suggests just such a paradigm is operating in the case of MDD. Diagnoses are made based solely on symptoms which are, according to this analysis, clearly akin to physical pain. Additionally, although emotional pain is a signal of difficulty interacting with the environment, diagnoses of MDD are generally made regardless of environmental and psychosocial stressors. In short, the BSM suggests there may be significant conceptual problems that underlie the medical model approach to depression.