The effects of stress and stress hormones on human cognition: Implications for the field of brain and cognition

Abstract

In this review, we report on studies that have assessed the effects of exogenous and endogenous increases in stress hormones on human cognitive performance. We first describe the history of the studies on the effects of using exogenous stress hormones such as glucocorticoids as anti-inflammatory medications on human cognition and mental health. Here, we summarize the cases that led to the diagnosis of glucocorticoid-induced ‘steroid psychosis’ in human populations and which demonstrated that these stress hormones could thus cross the blood–brain barrier and access the brain where they could influence cognition and mental health. We then summarize studies that assessed the effects of the exogenous administration of glucocorticoids on cognitive performance supported by the hippocampus, the frontal lobes and amygdala. In the second section of the paper, we summarize the effects of the endogenous release of glucocorticoids induced by exposure to a stressful situation on human cognition and we further dissociate the effects of emotion from those of stress on human learning and memory. Finally, in the last section of the paper, we discuss the potential impact that the environmental context to which we expose participants when assessing their memory could have on their reactivity to stress and subsequent cognitive performance. In order to make our point, we discuss the field of memory and aging and we suggest that some of the ‘age-related memory impairments’ observed in the literature could be partly due to increased stress reactivity in older adults to the environmental context of testing. We also discuss the inverse negative correlations reported between hippocampal volume and memory for young and older adults and suggest that these inverse correlations could be partly due to the effects of contextual stress in young and older adults, as a function of age-related differences in hippocampal volume.

Introduction

Stress is a popular topic these days. A week seldom passes without hearing or reading about stress and its deleterious effects on health. Given this negative impact of stress on human health, many types of stress management therapies have been put forward to decrease stress and thus, promote health. However, there is a great paradox in the field of stress research, and it relates to the fact that the popular definition of stress is very different from the scientific definition of stress. This has left a multitude of people and experts talking about, and working on, very different aspects of the stress response.

In popular terms, stress is mainly defined as time pressure. We feel stressed when we do not have the time to perform the tasks we want to perform within a given period of time. This time pressure usually triggers a set of physiological reactions that give us the indication that we are stressed. Although this definition is certainly accurate in terms of one component of the stress response, it is important to acknowledge that in scientific terms, stress is not equivalent to time pressure. If this were true, every individual would feel stressed when pressured by time. However, we all know people that seek time pressure in order to perform adequately and others that are extremely stressed by time pressure. This shows that stress is a highly individual experience that does not depend on a particular event such as time pressure, but rather, it depends on specific psychological determinants that trigger a stress response.