EFFECTS OF STRESS ON BEHAVIOUR AND SLEEP

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EFFECTS OF STRESS ON BEHAVIOUR AND SLEEP

Journal Title: Праці Наукового товариства ім. Шевченка - Year 2017, Vol 49, Issue

Abstract

Psychologists Yerkes and Dodson described already in 1908 the inverted-U shaped relationship between arousal and performance. When the level of arousal heightens, behavioural performance increases but only to a certain point. When the level of arousal, produced by stress, becomes too high, adequacy of behaviour decreases while sleep is affected. Physical and mental performance generally follows the level of circulating stress hormones, in particular the glucocorticoid hormone cortisol. The secretion of cortisol in response to a stressful event triggers a chain of events, ultimately leading to energy for ﬁ ght-or-ﬂ ight behaviour. Under non-stressed basal conditions, the level of cortisol follows a circadian pattern: a maximum in the morning, necessary for daily activities, with slowly declining levels during theday, and a trough during sleep. Cortisol binds to two glucocorticoid receptor subtypes: Type I with a high afﬁ nity and Type II with a lower afﬁ nity for cortisol. There are also differences in brain location between the types. The differences between the two subtypes results in a discrepancy of receptor occupation. During the nocturnal sleep trough all Type I receptors are occupied by the endogenous hormone, while during the morning wake peak Type 1 receptors are fully saturated and Type 2 receptors come into action. The mix of Type I and Type II occupation is also the situation by stressful events. The differential qualities of both receptors have created a new hypothesis about the cortisol effects on behaviour and sleep (De Kloet et al, 1999; Lupien et al, 2007). Elevated levels of cortisol due to stress have commonly detrimental effects on performance, such as on memory, but it is more than once reported that cortisol could have positive effects on cognition. The Type I/Type II ratio hypothesis suggests that performance by cortisol can be enhanced when Type I receptors are activated. However, when both Type I and Type II receptors are saturated, shifting the ratio towards Type II occupancy, performance and sleep are affected. It is in this way that the double function of cortisol as a sleep/ wake–hormone as well as a stress-hormone, can be understood. The hypothesis is now that the inverted-U shaped relationship between arousal and stress at one side and behavioural and cognitive performance at the other, might be explained by the presence of two different types of glucocorticoid receptors.

Authors and Affiliations

Anton Coenen

Keywords

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EP ID EP305071
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