The Effects of Chronic Stress on the Brain by Dr. Catherine Buchan
Our brain is wired for survival and reproduction (Gilbert & Choden, 2013). To facilitate this, we have an autonomic nervous system (ANS) regulated by the brain, which has two main parts, the parasympathetic nervous system (PNS), the “rest and repair” system and the sympathetic nervous system (SNS), or the “flight or fight” system. The PNS and the SNS are both involved in our response to stress. The PNS temporarily withdraws its “inhibitory effects”, which keep us in our resting state so that the SNS can respond to the stress (Rotenberg & McGrath, 2016).
In addition to the ANS, the stress response system also includes the hypothalamic–pituitary–adrenal axis (HPAA) (a hormonal system), which is an interaction between the hypothalamus, the pituitary gland and the adrenal glands (Chrousos, 2009). The SNS/HPAA response triggers a cascade of hormones (e.g. adrenalin; cortisol), more blood is pumped faster around the body, and some processes slow down temporarily (e.g. digestion; the immune response) in order to mobilise us into action rapidly, which all contribute to enabling us to “flee or fight”.
However, our bodies and minds were not designed to sustain long periods of SNS/HPAA activation, and particularly the bombardment of hormones such as cortisol. It was designed to facilitate brief periods of “hunting, gathering” and survival, followed by a return to our normal resting state. Hence, repeated activation of the SNS/HPAA results in chronic stress. Normally, the PNS counteracts the SNS/HPAA, as mentioned, but with chronic stress it does not, which leads to neurotoxicity, which subsequently negatively affects changes in the amygdala and cingulate cortex (Kim & Won, 2017). It also negatively affects the hippocampus in particular (Ortiz & Conrad, 2018). The hippocampus, along with the amygdala, are involved with memory for example. Thus, continual activation of the SNS/HPAA detrimentally affects the hippocampus by wearing it down and this negatively affects our ability to form new memories (Hanson, 2009).
Cortisol is released during activation of the SNS/HPAA, as mentioned and it has also been shown to have a detrimental effect on memory and cognition because it curbs the activity of the hippocampus, which stops suppressing the amygdala under these conditions, which results in more cortisol being released (Hanson, 2009). Moreover, cortisol binds to receptors that are found in the hippocampus and amygdala, which are important brain regions for learning and memory and high levels of cortisol appear to negatively impact memory, making it more difficult to recall specific memories (Munoz, 2013)
Not only does repeated activation of the SNS/HPAA effect memory and cognition, it also alters the areas of the brain are connected with regulating our emotions (the hippocampus, amygdala and anterior cingluate cortex) (Kim & Won, 2017). Hence, the effects of chronic stress on the brain include links to mood-related problems, including anxiety and major depression too (Smith & Vale, 2006).
Another aspect of this is that the continual SNS/HPAA activation with chronic stress over stimulates the amygdala. Consequently, the amygdala becomes more sensitive to what appear to be threats, which results in a further increase in activation of the SNS/HPAA, and this further increases the amygdala’s sensitivity (Hanson, 2009). Because the amygdala is central to managing our response to fear, it means we then often experience more anxiety (Wilson, 2013).
Furthermore, repeated activation of the SNS/HPAA with chronic stress decreases the production of the feel-good hormones dopamine and serotonin (which regulate our mood and emotions), and so we are more susceptible to low mood and depression (Wilson, 2013). Consequently, if we do not take action to regularly de-stress (i.e. with mindfulness etc.), we become chronically stressed which negatively impacts the structure and function of the brain, as demonstrated.
Chrousos, G. (2009). Stress and disorders of the stress system Nature Reviews Endocrinology, 5 (7), 374-381.
Gilbert, P. and Choden. (2013). Mindful Compassion: Using the Power of Mindfulness and Compassion to Transform Our Lives. Little, Brown Book Group.
Hanson, R. (2009). Buddha’s Brain: The practical neuroscience of happiness, love and wisdom. New Harbinger Publications, Inc.
Kim, Y. & Won, E. (2017). The influence of stress on neuroinflammation and alterations in brain structure and function in major depressive disorder. Behavioural Brain Research, 329, 6-11.
Munoz, L. M. P. (2013). Stress Hormone Hinders Memory Recall. Cognitive Neuroscience Society: Retrieved from: https://www.cogneurosociety.org/cortisol_memory/
Ortiz, J. B. & Conrad, C. D. (2018). The impact from the aftermath of chronic stress on hippocampal structure and function: Is there a recovery? Frontiers in Neuroendocrinology, 49, 114-123.
Rotenberg, S. and McGrath, J. J. (2016). Inter-relation between autonomic and HPA axis activity in children and adolescents. Biological Psychology, 117, 16-25.
Smith, S. M. & Vale, W. W. (2006). The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress. Dialogues in Clinical Neuroscience, 8, 383–395.
Wilson, A. (2013). Mindfulness meditation and the brain. Huffington Post: Retrieved from http://www.huffingtonpost.com/kripalu/mindfulness-meditation_b_3238677.