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Original Articles
Introduction
Inter-individual differences in brain structure and function are partly due to environmental factors (Davidson & McEwen, 2012). Psychosocial stress is one such factor that may lead to neural changes, and these alterations can have both adaptive and maladaptive consequences (McEwen & Gianaros, 2011). Although most people show resilience to psychosocial stress (Gillespie et al. 2009), the experience of stress may result in traumatic memories and development of neuropsychiatric disorders (Kessler et al. 1997; Wang et al. 2012). Furthermore, psychosocial stress can lead to long-term morphological and functional changes in the brain (Bremner, 2006; Tottenham et al. 2010), which may underlie cognitive and behavioural symptoms observed in mood and anxiety disorders.
Two limbic brain regions that are thought to be particularly vulnerable to psychosocial stress are the hippocampus (McEwen, 2007) and the amygdala (Roozendaal et al. 2009). Experimental animal studies have shown opposing effects of chronic stress on these two structures: after the experience of a stressor, the hippocampus shows impaired neurogenesis and atrophy or remodelling of the apical dendrites of pyramidal neurons in the CA3 region (McEwen, 2001), whereas the same stressor causes dendritic growth in basolateral amygdala (Vyas et al. 2002). In humans, smaller hippocampal volume is a recurrent finding in post-traumatic stress disorder (PTSD; Bremner et al. 2008) and in young and middle-aged adults who experienced stressful events during childhood (Teicher et al. 2012). With regard to amygdala volume, inconsistent findings have been reported, where both smaller (Woon & Hedges, 2009; Morey et al. 2012) and larger (Tottenham et al. 2010; Kuo et al. 2012) volumes have been observed in patients with PTSD and in relation to psychosocial stress.
There is increasing evidence that the timing of a stressor determines how much impact it will have on the brain (Teicher et al. 2006). Experience of stress is thought to have a detrimental effect on the brain especially during stages of life when the brain undergoes major changes, i.e. development in early life and deterioration in late life (Wolkowitz et al. 2010). Moreover, the effect of childhood stress can influence the brain well into adulthood, although only a few studies have investigated such long-term associations (van Harmelen et al. 2010).
Finally, stress may have different...