Self-esteem, locus of control, hippocampal volume, and cortisol regulation in young and old adulthood

Abstract

Self-esteem, the value we place on ourselves, has been associated with effects on health, life expectancy, and life satisfaction. Correlated with self-esteem is internal locus of control, the individual's perception of being in control of his or her outcomes. Recently, variations in self-esteem and internal locus of control have been shown to predict the neuroendocrine cortisol response to stress. Cumulative exposure to high levels of cortisol over the lifetime is known to be related to hippocampal atrophy. We therefore examined hippocampal volume and cortisol regulation, to investigate potential biological mechanisms related to self-esteem. We investigated 16 healthy young (age range 20–26 years of age) and 23 healthy elderly subjects (age range 60–84 years). The young subjects were exposed to a psychosocial stress task, while the elderly subjects were assessed for their basal cortisol regulation. Structural Magnetic Resonance Images were acquired from all subjects, and volumetric analyses were performed on medial temporal lobe structures, and whole brain gray matter. Standardized neuropsychological assessments in the elderly were performed to assess levels of cognitive performance, and to exclude the possibility of neurodegenerative disease. Self-esteem and internal locus of control were significantly correlated with hippocampal volume in both young and elderly subjects. In the young, the cortisol response to the psychosocial stress task was significantly correlated with both hippocampal volume and levels of self-esteem and locus of control, while in the elderly, these personality traits moderated age-related patterns of cognitive decline, cortisol regulation, and global brain volume decline.

Introduction

Self-esteem is a broadly defined personality variable referring to the degree to which an individual values and accepts him- or herself. Low self-esteem has been associated with a host of negative life outcomes, including substance abuse, delinquency, unhappiness, depression, eating disorders, and worsened recovery after illnesses (see Hoyle et al., 1999, Leary and McDonald, 2003). High self-esteem has been associated with positive characteristics such as initiative, strong coping skills, persistence in the face of challenges, happiness, and longevity (Baumeister et al., 2003). In geriatric research, the suggestion has been made that a positive self-concept may play a key role in the model of successful aging, predicting independence, cognitive stability, and general health in old age (Baltes and Baltes, 1990, Markus and Herzog, 1991).

Little is known about possible biological mechanisms underlying self-esteem, or underlying the association between self-esteem, and health and disease. One likely candidate is the set of structures and systems relating to people's reactions to stress. Low self-esteem is associated with greater amounts of perceived daily hassles and chronic stressors, even after correcting for environmental factors, occupation, age, and gender. Conversely, high self-esteem tends to be strongly associated with internal locus of control, or the confident perception that one's outcomes are determined by one's actions (DeLongis et al., 1988, Lo, 2002, Petrie and Rotheram, 1982, Whisman and Kwon, 1993). These personality variables have been found to be predictive of people's neuroendocrinological reactions to stressful social situations. In a previous study, we demonstrated the importance of self-esteem in the cortisol stress response by showing that in a mental challenge task only the subjects with low self-esteem and low levels of internal locus of control exhibited a significant cortisol response (Pruessner et al., 1999b). We further found that these personality variables predicted the ability to habituate to repeated psychosocial stress, with subjects with low levels of self-esteem and low internal locus of control showing continuous high cortisol stress responses (Kirschbaum et al., 1995).

In the current research, we sought to investigate a central nervous system (CNS) characteristic possibly related to cortisol and personality variables, by examining the hypothesis that individuals with low self-esteem and low internal locus of control would have smaller hippocampal volumes. Previous findings have demonstrated that across the lifetime, high stress loads can impair health, with a specific effect on the CNS via the “allostatic load” model (McEwen, 1998, Schulkin et al., 1998). Briefly, chronic perceived stress can lead to poor habituation of the hypothalamic–pituitary–adrenal (HPA) axis and dysregulation of glucocorticoid (i.e., cortisol) release. Documented effects of stress include impairment and damage to specific brain structures via the action of neurotoxic glucocorticoids (Sapolsky, 1996, Watanabe et al., 1992, Woolley et al., 1990). Glucocorticoids further disrupt the cellular metabolism, via excitatory amino acids and glutamate accumulation. They also affect neuronal tissue by disruption of BDNF expression (Nibuya et al., 1995, Schaaf et al., 2000). Over time, dysregulation of glucocorticoid release, in conditions such as chronic pain or burnout, can take the form of a distorted diurnal pattern involving reduced cortisol response upon wakening but increased reactivity to threat. The hippocampus is the brain structure that appears particularly susceptible to damage as a result of chronic stress, due to a high density of receptors for glucocorticoids. We therefore examined the correlation between hippocampal volume, basal glucocorticoid regulation, and self-esteem and locus of control, in a sample of healthy elderly subjects, selecting individuals across a relatively wide age range to investigate the long-term relationship between self-esteem, locus of control and hippocampal volume. We also assessed the association between hippocampal volume and both self-esteem and locus of control in a sample of young subjects, to determine the relationships among these variables earlier in life. In the young subjects, we assessed acute rather than basal glucocorticoid regulation, by conducting psychosocial stress testing with accompanying cortisol assessment.

We hypothesized that in healthy elderly subjects, low self-esteem and low internal locus of control would be linked to smaller hippocampal volume, and signs of cortisol dysregulation. We assessed the cortisol response to awakening in the elderly, which has been recently reported to be associated with HC integrity such that HC damage predicts lower levels of cortisol in response to awakening (Buchanan et al., 2004, Wolf et al., 2005). In the sample of young adults, we were interested in examining whether self-esteem and locus of control would moderate the acute cortisol stress response (thereby replicating earlier studies), and to investigate whether these variables would be linked to hippocampal volume in young subjects as well.