THE ROLES OF ALLOSTASIS AND ALLOSTATIC LOAD:



THE ROLES OF ALLOSTASIS AND ALLOSTATIC LOAD

Allostasis is defined as the adaptation of the nervous, endocrine and immune systems to maintain stability through change (triggered, for example, by unpredictable events, such as conflict in social hierarchies and competition for resources, or predictable events, such as seasonal changes). An inefficiently managed adaptation is referred to as allostatic overload (Korte et al., 2005).

Allostatic systems promote adaptation to stressful experiences and are generally most useful when rapidly mobilized and terminated. When they are prolonged or not terminated promptly, allostatic systems undermine mental and physical health—primarily because of their effects on brain plasticity. The inability to engage allostatic systems when needed also produces a load on the body, because the normal protection afforded by these systems is lacking. An important aspect of Allostasis and allostaticload is the notion of anticipation. Here, anticipation implies psychological states, such as apprehension, worry, and anxiety, as well as cognitive preparation for a forthcoming event. Anticipation arising from neural activity within the brain can drive the output of allostatic bio mediators, and it is likely that states of prolonged anxiety and anticipation can result in allostatic load (Schulkin et al., 1994). Other important aspects of individual responses to stress in relation to Allostasis and allostatic load are health-damaging and health-promoting behaviours such as smoking, alcohol consumption, sleep, diet, and physical activity, collectively called lifestyle behaviours.

There are four types of allodynamic and physiological responses that may contribute to and reflect allostatic load (Figure 2). These include (a) repeated “hits” from multiple stressors, (b) a lack of adaptation or habituation, (c) prolonged response due to delayed shutdown, and (d) inadequate response that leads to compensatory hyperactivity of other mediators.  These forms of allodynamic response, which can contribute to allostatic load, are mediated by the brain and target the brain. Importantly, conditions of allostatic load that adversely affect the brain are associated with forms of neural plasticity that are amenable to prevention and intervention.



Figure 3: Central role of the brain in allostasis and the behavioral and physiological response to stressors (McEwen, 1998).

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