Δευτέρα, 16 Οκτωβρίου 2017

The effect of stress hormones on cognition

Stress is the primitive fight or flight response: when faced with an unknown or dangerous situation (a stressor) individuals are becoming prepared to either deal with it, or run away. The organism is reacting in a certain way, in order to ensure the best possible outcome of the situation, by using all means at its disposal.
During the fight or flight response, changes in the body occur: elevated heart rate, sweating, increased respiration rate and blood pressure levels. All these changes in the body- the physical expression of stress- prepare it to either fight or flight from the situation (Greenberg, 2012).
The responses of the body when it deals with a stressor are triggered by certain hormones. When stressed, corticotropin- releasing hormone (CRH) is released in the hypothalamus. The CRH leads to the release of adrenocorticotropin (ACTH) from the pituitary gland. The ACTH in turn, after traveling through the blood, causes the release of glucocorticoids, thus cortisol (in humans), and the catecholamines, including adrenaline and nor-adrenaline. These two are categories of stress hormones that exist in the adrenal glands, and they are those that trigger the responses of the body. These classes of hormones have been found to have a variety of effects not only on the body but on the brain as well- they have an impact on several aspects of cognition (Fiocco, Lupien, Maheu, Schramek, 2007).
In a paper by Lupien and colleagues, the effects of stress hormones on cognition were extensively analyzed. The researchers took a ‘historical’ perspective, reviewing literature from the 60s onward. They mainly focused on glucocorticoids, since they are able to cross the blood- brain barrier and reach the brain. Gluccorticoids, when induced exogenously can have an effect on vigilance, on declarative memory (and the hippocampus), on working memory and memory of emotional events (and the frontal lobe). Similarly, their literature review on the endogenous release of glucocorticoids, when facing a stressor, showed that they affect several aspects of cognition. The increase of glucocorticoids can lead to enhanced emotional memory (which is also influenced by catechoalmines). Also, alterations in glucocorticoid levels have an effect on declarative memory: both too high and too low levels can impair the explicit memory performance. Taking these finding together, it can be argued that the effect of glucocorticoids in memory depends on the content of the material (emotional memory is improved, but memory on neutral stimuli is reduced), and that any type of extreme- whether an increase or a decrease on the levels of glucocorticoids can alter memory performance. It is worth noting that catecholamines (noradrenaline) can also lead to an impaired declarative memory, but few studies have been conducted on that. Extending that, Lupien and colleagues argued that glucocorticoids can have an impact on hippocampal volume- the ‘memory location’ of the brain (Fiocco, Lupien, Maheu, Schramek, 2007). More recently, it has been argued that glucocorticoids have an effect on all stages of memory, such as on encoding and retrieval, and on different types of memory, ranging from long term memory to working memory. Still, the manner in which they do so is as explained above: the extremes decrease performance, and nature of material matters. Overall, glucocorticoids that exist due to stressors can have an impact on the process of learning, memory (and implicitly on emotion therefore) and executive functioning. Catecholamines assist these effects (Wirth, 2015).
Returning to Lupien, a final point that was made was that stressors are subjective: something that may be very stressful to one individual, and thus cause the fight or flight response and everything that comes with it, may not be for another person. These researchers argued that some individuals are more prone to experience events and situations as stressors. They, in turn, are experiencing the effects of stress on cognition more often and more intensively. When these effects are experienced often they can lead to impaired cognition in the general level, as glucocorticoids leave their mark on the brain. So stress hormones can assist the organism and its cognition during the time of crisis, but can harm the organism, and impair its cognitive functioning in many levels when experienced often.
This idea brings back to mind the evolutionary importance of stress: it allows a better performance in an urgent situation. Yet the constant experience of stressors can harm both the brain and the body: studies reveal that chronic stress can cause not only cognitive impairment but also increase the chances for a variety of diseases, such as heart problems. This should make us reconsider the concept of stress, and its (increasingly large) role in our everyday vocabulary, and in our lives.

Fiocco, A., Lupien, S., J., Maheu, F., Schramek, T., E., Tu, M., (2007). The effects of stress and stress hormones on human cognition: Implications for the field of brain and cognition, Brain and Cognition, 65, 209-237

Greenberg, J., S., (2012). Comprehensive Stress Management, US, McGraw- Hill Education


Wirth, M., M., (2015). Hormones, stress, and cognition: The effects of glucocorticoids and oxytocin on memory, Adaptive Human Behavior and Physiology, 1, 177-201

Δεν υπάρχουν σχόλια:

Δημοσίευση σχολίου