Review
Rising rates of depression in today's society: Consideration of the roles of effort-based rewards and enhanced resilience in day-to-day functioning

https://doi.org/10.1016/j.neubiorev.2005.09.002Get rights and content

Abstract

Despite the existence of a vastly improved health care system and a multi-billion dollar antidepressant industry, the rates of depression in the US remain alarmingly high. An exploration of lifestyle changes over the past century suggests that the level of physical activity necessary to provide life's basic resources, referred to as effort-based rewards, has diminished in our industrialized, technologically advanced, service-oriented society. The evolution of the accumbens–striatal–cortical circuitry and its modulating neurochemicals in our ancestors played a significant role in sustaining the continued effort critical for the acquisition of resources such as food, water and shelter; consequently, vast reductions in the degree of physical activity required to obtain necessary resources in today's society likely lead to reduced activation of brain areas essential for reward/pleasure, motivation, problem-solving, and effective coping strategies (i.e. depressive symptomology). Comparative cultural and gender analyses reinforce the significant role of effort-based rewards in mood regulation, suggesting that minimal engagement in such endeavors leads to compromised resilience upon exposure to life's stressful challenges. If physical activity is indeed important in the maintenance of mental health, increased emphasis on behavioral and behavioral/cognitive preventative life strategies, as opposed to an emphasis on psychopharmacological strategies directed at very specific neurochemicals after the onset of depression, should be adopted as protective measures against the onset of depressive symptomology. Thus, strategies that include more global neurobiological activation in the relevant context of directed efforts provide a fresh perspective for depression research.

Introduction

Happiness, then, is something final and self-sufficient, and is the end of action. (Aristotle, Nicomachean Ethics, 350 B.C.)

Over the course of the last century, developing countries have enjoyed unprecedented gains in prosperity and health. Life expectancies have increased by over 50% in countries such as Egypt and India; additionally, diseases such as smallpox, once killing millions annually, have been eradicated (Kleinman and Cohen, 1997, Seligman, 1990). Examples of such strides in physical well-being are abundant; however, this progress has not extended to mental health. Even though a multi-billion dollar antidepressant industry exists, The World Health Organization estimates that depressive and anxiety disorders lead the list of mental illnesses across the globe—and these disorders are responsible for approximately 25% of all visits to health care centers around the world. Currently, it is estimated that (Parker et al., 2001) 121 million people are suffering from depression. In the US, depression is one of the most prevalent forms of mental illness with lifetime rates ranging from approximately 10 to 22% for men and women, respectively (World Health Organization, 2005, Kessler et al., 2003, Un, 2004). The irony that, in the midst of unprecedented affluence and a substantial antidepressant pharmaceutical industry, rates of depression are continuing to rise, presents a conundrum to researchers, requiring further exploration of relevant factors related to the onset of depression.

As we have recently entered the new millennium, perhaps it is beneficial to step back and examine the larger picture of depression that has emerged over the past century. A flurry of research activity has emphasized the role of serotonin in the onset of depression and, no doubt, we have acquired an immense amount of information about this neurochemical system. In spite of the marketing success of antidepressants, however, many researchers have questioned the efficacy of this therapeutic approach. Researchers have yet to identify a biological test of depression; additionally, a clear relationship between serotonergic activity and depressive symptoms has yet to be firmly established. These observations have prompted many scientists and clinicians to question the pervasive use of antidepressants, especially SSRIs, in today's society (Healy, 2004, Healy, 1997, Kirsch and Antonuccio, 2002, Valenstein, 1998). As we contemplate the aforementioned increases in depression over the past century, an important question arises as we consider how the serotonergic system, or any other neurobiological system for that matter, deemed to be a critical factor related to the onset of depression, has changed so drastically in such a short period of time to accompany the changing rates in depression. Aside from mutations, such rapid evolutionary alterations of essential biological systems are unprecedented in mammals. Focusing on the bigger picture of human lifestyle, however, it is evident that in many cultures across the world there have been drastic changes over the past several generations in the way humans live. Accordingly, the mental health field has been criticized by anthropologists and others for focusing too narrowly on the biological causes of depression at the cost of discounting variables such as culture and socioeconomic status. In fact, mental health researchers have been challenged to ‘formulate a perspective that better explains the interplay among the socioeconomic, cultural, and biological aspects of mental illness’ (Kleinman and Cohen, 1997, p. 89)

The purpose of this theoretical article is to attempt to meet the aforementioned challenge by developing a perspective that incorporates neurobiological evidence and sociocultural variables to provide new insights into causes of depressive symptoms and, more importantly, consider strategies leading to protection against the onset of these symptoms. To accomplish this goal we will consider (1) lifestyle and cultural variables providing clues about rates of depression, emphasizing alterations in the amount of physical effort required to survive in contemporary societies (2) the neurobiology of the reward system of the brain and its interconnectedness with brain areas sustaining directed effort, (3) the evolution of brain areas supporting manual dexterity and tool use and implications for mood alterations, and (4) a reassessment of current therapeutic approaches (in light of the proposed behavioral effectiveness perspective of depressive symptoms) including serious consideration of the value of gaining more neurobiological information about response strategies corresponding with resilience, as opposed to the current focus of response strategies accompanying depression.

Section snippets

Influence of lifestyle and cultural variables in the onset of depression

Two epidemiological studies of depression conducted in the 1970s provided strong evidence that lifestyle changes over the past century were worth examining as potential causes in increased rates of depression. These studies focused on lifetime prevalence of depression in a cross-sectional design. Because common wisdom suggests that older individuals would have more opportunities and reasons to develop depression; higher rates of depression were hypothesized in older populations. Surprisingly,

Neurobiological mechanisms of effort-based rewards: relevance for depressive symptomology

A majority of the symptoms the DSM-IV-TR lists as criteria for obtaining a diagnosis of depression has been associated with known functions of the basal forebrain structure, the nucleus accumbens (American Psychiatric Association, 2000). Mogenson described the unique aspects of this structure several decades ago, noting that the nucleus accumbens was anatomically positioned between the brain's motor system (striatum) and emotional circuit (limbic system) (Mogenson et al., 1980). Considering

The role of manual dexterity in the evolution of effort-based rewards: has a clue to increased rates of depression been in our hands all along?

Perhaps it was when our primate ancestors descended from the trees about 2.5 million years ago that our brains, wrists, and hands began morphing into their contemporary structure and form that provided the fine-tuned motor skills necessary for sophisticated tool use. Without the need for arboreal locomotion, primates' long curved fingers and short thumbs were no longer needed and the more flexible wrist, short straight fingers and long thumbs began to evolve to maximize stability while gripping

Reassessment of current therapeutic approaches for depression

Currently, consumers who approach two US authorities on mental illness, i.e. the National Institutes of Mental Health (NIMH), (2005) and the National Alliance on Mental Illness (NAMI), (2005) quickly learn that the most information provided about treatment for depression on their respective websites concerns medications (e.g. SSRIs, MAOIs) while considerably less information is provided about other forms of therapy such as psychotherapy and electroconvulsive therapy. When one considers the

Conclusions

Perhaps the well-known analogy of a ‘drunk’ and the lamppost sheds some light on the current challenge of discerning the most meaningful causes and courses of action for depression. In this analogy, a police officer sees a drunk stumbling around a lamppost and asks what the problem is. When the drunk replies that he has lost his car keys, the police officer asks exactly where they were lost. The officer is confused when the drunk replies that they were lost several hundred yards away from the

Acknowledgements

This work was supported by the R-MC Chenery Fellowship and the R-MC Psychology Department. Additionally, the input provided by Dr Gary Lambert is greatly appreciated.

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