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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