Memory performance is related to the cortisol awakening response in older people, but not to the diurnal cortisol slope

The Cortisol Awakening Response: Regulation and Functional Significance

In healthy individuals, the majority of cortisol secretion occurs within several hours surrounding morning awakening. A highly studied component of this secretory period is the cortisol awakening response (CAR), the rapid increase in cortisol levels across the first 30 to 45 minutes after morning awakening. This strong cortisol burst at the start of the active phase has been proposed to be functional in preparing the organism for the challenges of the upcoming day. Here, we review evidence on key regulatory and functional processes of the CAR and develop an integrative model of its functional role. Specifically, we propose that, in healthy individuals, the CAR is closely regulated by an intricate dual-control system, which draws upon key circadian, environmental, and neurocognitive processes to best predict the daily need for cortisol-related action. Fine-tuned CAR expression, in turn, is then assumed to induce potent glucocorticoid action via rapid nongenomic and slower genomic pathways (eg, affecting circadian clock gene expression) to support and modulate daily activity through relevant metabolic, immunological, and neurocognitive systems. We propose that this concerted action is adaptive in mediating two main functions: a primary process to mobilize resources to meet activity-related demands and a secondary process to help the organism counterregulate adverse prior-day emotional experiences.

Subjective memory complaints in young people: the role of resilience

OBJECTIVE

Little is known about the origin and associated factors of subjective memory complaints (SMCs) in the young population, although they might be closely related to the psychophysiological states produced by stress exposure, such as anxiety and depression. In this regard, resilience has been related to a reduction in these negative states, as well as to more adaptive hypothalamic-pituitary-adrenal (HPA) axis functioning. We aimed to investigate the importance of depression, anxiety, and HPA axis activity in SMCs in the young population. We also analysed the relationship between resilience and SMCs through the mediation of depression, anxiety, and the cortisol awakening response (CAR).

DESIGN

To do so, we measured SMCs, depression and anxiety states, resilience, and the CAR in 77 healthy young people.

RESULTS

Both depression and anxiety were associated with SMCs. In addition, greater resilience was related to fewer SMCs through depression and anxiety. However, the CAR was not related to SMCs, and it did not mediate the relationship between resilience and SMCs.

CONCLUSION

These results suggest that negative affective states have greater importance in SMCs than HPA functioning in this age group, and they also highlight the importance of resilience in the psychological adjustment to stressful situations.

Feelings of tense and risk of incident dementia: A prospective study of 482,360 individuals

BACKGROUND

The relationship between feelings of tense, as a significant emotional distress, and dementia remains unclear. This study aimed to evaluate the association between feelings of tense and dementia.

METHODS

In UK Biobank, feelings of tense were measured with a standard item. The primary outcome was all cause of dementia (ACD) and its subtypes (Alzheimer's disease (AD), vascular dementia (VD), and other dementia). Cox regression models analyzed the association between feelings of tense and dementia risk, while linear regression examined the correlation with neuroimaging outcomes. The potential association and joint effects of AD and tenseness were evaluated based on the established genetic risk score (GRS).

RESULTS

During a median follow-up of 12.7 years among 482,360 participants, 7331 dementia cases were identified. Individuals with feelings of tense had a significantly increased risk of ACD (HR, 1.194; 95 % CI: 1.115-1.278), VD (HR, 1.164; 95 % CI: 1.007-1.346), and other dementia (HR, 1.181; 95 % CI: 1.081-1.289), but not AD in multi-adjusted models. This association persisted across various sensitivity analyses and exhibited some heterogeneity in subgroup analyses. Furthermore, feelings of tense are associated with total brain volume shrinkage, higher white matter hyperintensities, and decreased partial subcortical volume, particularly in the hippocampus. No interaction between tenseness and AD genetic susceptibility was observed (P for interaction =0.346).

LIMITATIONS

Our study only considered feelings of tense measured at a one-time point.

CONCLUSIONS

Our findings demonstrate a significant association between feeling of tense and elevated dementia risk, indicating that tenseness could serve as a modifiable psychological determinant for dementia.

Life-course stress, cognition, and diurnal cortisol in memory clinic patients without dementia

AIMS

To examine associations of life-course stress with cognition and diurnal cortisol patterns in older adulthood, as well as potential mediation effects of diurnal cortisol patterns and perceived stress on the association between life-course stress and cognition.

METHODS

127 participants without dementia were selected from a cohort of Swedish memory clinic patients. Cross-sectional associations between scores on two chronic stress questionnaires (perceived stress, stressful life events (SLEs)), five cognitive domains (overall cognition, memory, working memory, processing speed, perceptual reasoning), and two measures of diurnal cortisol patterns (total daily output, diurnal cortisol slope), as well as potential mediation effects of diurnal cortisol patterns and perceived stress on associations between life-course stress and cognition, were assessed using linear regressions.

RESULTS

Greater lifetime exposure to SLEs was associated with worse memory, working memory, and processing speed performance, but not with diurnal cortisol patterns. A greater number of SLEs in late childhood was associated with worse working memory and processing speed, while a greater number of SLEs in non-recent adulthood were associated with better overall cognition and perceptual reasoning. Greater perceived stress was associated with a flattened diurnal cortisol slope, but not with cognition. No evidence for interplay between self-reported and physiological stress markers was found in relation to cognition, although there appeared to be a significant positive indirect association between economic/legal SLEs and the diurnal cortisol slope via perceived stress.

CONCLUSIONS

The associations between SLEs and cognition depend on the period during which SLEs occur, but seem independent of late-life cortisol dysregulation.

Loneliness during the post-confinement period: The significance of social living conditions for stress biomarkers and memory

In the aftermath of the COVID-19 lockdown, concerns about the impact of loneliness and reduced social interactions on mental health have arisen. This study explored the repercussions of post-lockdown social restrictions across psychological (loneliness, perceived stress, and depressive symptoms), biological (hair cortisol and cardiovascular activity), and cognitive dimensions (subjective memory complaints and working, declarative, and prospective memory), with a specific emphasis on perceived loneliness and the living situation. The study included 45 students: 23 (mean age = 25.69 years) in the Alone Group (AG), who experienced significant family changes and international relocation, and 22 (mean age = 25.50 years) in the Not Alone Group (NAG), who maintained their nuclear family and did not move from their home country. We assessed heart rate variability (HRV) before, during, and after immediate memory evaluations using time-domain (the square root of the mean, RMSSD) measures. The analysis revealed no significant group differences in telematic contact with family and friends, perceived stress, or depression. However, the AG participants reported fewer face-to-face interactions and greater perceived loneliness compared to the NAG. Additionally, the AG group exhibited slightly higher hair cortisol levels and worse working memory (WM) and prospective memory (PM) performance. Importantly, no significant associations were observed between memory outcomes and stress biomarkers. However, a significant interaction effect of loneliness in the relationship between hair cortisol levels and PM was found. That is, hair cortisol concentrations were negatively related to PM when participants perceived high and moderate loneliness. This interaction was absent in the working and declarative memory domains. In summary, these findings underscore the intricate interplay between loneliness, cortisol, and memory, emphasizing the need for comprehensive research on the complex mechanisms governing these multifaceted relationships.

Effects of COVID-19 Lockdown on Nutritional, Functional and Frailty Biomarkers of People Living in Nursing Homes. A Prospective Study

BACKGROUND

Nursing home residences suffered a lockdown from the beginning of the COVID-19 pandemic. The present study prospectively evaluates the frailty, functional, and nutritional statuses of nursing home residents.

METHODS

Three hundred and one residents from three nursing homes took part in the study. Frailty status was measured using the FRAIL scale. Functional status was evaluated using the Barthel Index. Additionally, Short Physical Performance Batter (SPPB), SARC-F, hand-grip strength, and gait speed were also evaluated. Nutritional status was determined using the mini nutritional assessment test (MNA) and several anthropometrical and biochemical markers.

RESULTS

Mini Nutritional Assessment test scores decreased in 20% throughout the confinement (p < .001). Barthel index, SPPB and SARC-F scores also decreased, although to a lesser extent, reflecting a decrease in functional capacity. However, both anthropometric parameters, hand grip strength and gait speed, remained stable throughout confinement (p > .050 in all cases). Morning cortisol secretion significantly decreased by 40% from baseline to post-confinement. A significant reduction in daily cortisol variability was observed, which may suggest increased distress. Fifty-six residents died during the period of confinement (81.4% survival rate). Sex, FRAIL and Barthel Index scores were significant predictors of resident survival.

CONCLUSION

After the first COVID-19 blockade, several alterations in residents' frailty markers were observed, which were small and potentially reversible. However, many of the residents were pre-frail after the lockdown. This fact highlights the need for preventive strategies to reduce the impact of future social and physical stressors on these vulnerable individuals.

Sleep and dreaming in the light of reactive and predictive homeostasis

Dreams are often viewed as fascinating but irrelevant mental epihenomena of the sleeping mind with questionable functional relevance. Despite long hours of oneiric activity, and high individual differences in dream recall, dreams are lost into oblivion. Here, we conceptualize dreaming and dream amnesia as inherent aspects of the reactive and predictive homeostatic functions of sleep. Mental activity during sleep conforms to the interplay of restorative processes and future anticipation, and particularly during the second half of the night, it unfolds as a special form of non-constrained, self-referent, and future-oriented cognitive process. Awakening facilitates constrained, goal-directed prospection that competes for shared neural resources with dream production and dream recall, and contributes to dream amnesia. We present the neurophysiological aspects of reactive and predictive homeostasis during sleep, highlighting the putative role of cortisol in predictive homeostasis and forgetting dreams. The theoretical and methodological aspects of our proposal are discussed in relation to the study of dreaming, dream recall, and sleep-related cognitive processes.

Cortisol, cognition and Alzheimer's disease biomarkers among memory clinic patients

Objective

This study aims to investigate the relationship between diurnal cortisol patterns, cognition and Alzheimer's disease (AD) biomarkers in memory clinic patients.

Method

Memory clinic patients were recruited from Karolinska University Hospital in Sweden (n=155). Diurnal cortisol patterns were assessed using five measures: awakening levels, cortisol awakening response, bedtime levels, the ratio of awakening to bedtime levels (AM/PM ratio) and total daily output. Cognition was measured in five domains: memory, working memory, processing speed, perceptual reasoning and overall cognition. AD biomarkers Aβ42, total tau and phosphorylated tau were assessed from cerebrospinal fluid (CSF). Cognition was measured at follow-up (average 32 months) in a subsample of participants (n=57).

Results

In assessing the associations between cortisol and cognition, higher awakening cortisol levels were associated with greater processing speed at baseline. No relationship was found between diurnal cortisol patterns and change in cognition over time or CSF AD biomarkers in the total sample. After stratification by CSF Aβ42 levels, higher awakening cortisol levels were associated with worse memory performance in amyloid-positive participants. In amyloid-negative participants, higher bedtime cortisol levels and a lower AM/PM ratio were associated with lower overall cognition, greater awakening cortisol levels were associated with better processing speed, and a higher AM/PM ratio was associated with better perceptual reasoning. Additionally, higher awakening cortisol levels were associated with lower CSF Aβ42 levels in amyloid-positive participants, while higher bedtime cortisol levels and a lower AM/PM ratio were associated with higher CSF total tau in amyloid-negative participants.

Conclusions

Our findings suggest that diurnal cortisol patterns are associated with cognitive function and provide new insights into the association between diurnal cortisol patterns and AD-related CSF biomarkers. Further research is needed to examine the complex relationship between cortisol, cognition and brain pathology.

Mediation of perceived stress and cortisol in the association between neuroticism and global cognition in older adults: A longitudinal study

Neuroticism has been associated with a greater dementia risk, but its association with cognitive decline in healthy older adults remains unclear. Stress has been proposed as one of the mechanisms that could explain this relationship. Our aim was to analyse, in healthy older people, the mediating role of perceived stress and the Hypothalamic-Pituitary-Adrenal (HPA) axis in the association between neuroticism and global cognition. At Waves 1 and 2 (4-year follow-up), 87 older people (49.4% women; M age = 65.08, SD = 4.54 at Wave 1) completed a neuropsychological battery and the Perceived Stress Scale (PSS), and provided saliva samples on two (Wave 1) and three (Wave 2) consecutive days to measure the wake-to-bed slope. In Wave 2, neuroticism was assessed with the NEO-Five-Factor Inventory. PSS, but not the wake-to-bed slope, mediated the negative associations between neuroticism and global cognition (Waves 1, 2 and change). Regarding gender differences, PSS (Waves 1, 2 and change) and the wake-to-bed slope (Wave 2 and change) mediated these associations in men. Our results suggest that perceived stress and HPA-axis dysregulation could act as mechanisms underlying the association between neuroticism and cognitive functioning and decline, at least in older men.

Diurnal cortisol secretion and health-related quality of life in healthy older people

Several studies have demonstrated that a dysregulated hypothalamic-pituitary-adrenal (HPA) axis is related to worse health status (e.g., depression, posttraumatic stress, or diabetes, among others). However, less is known about the association between the individual's perception of their own health status and HPA-axis functioning in healthy older people. The aim of the present study was to examine the relationship between HPA-axis functioning and health-related quality of life (HRQoL) in healthy older people. To do this, 140 healthy older people (69 men and 71 women) from 56 to 76 years old collected eight saliva samples on two consecutive weekdays to measure the diurnal cortisol cycle (i.e. awakening cortisol levels, cortisol awakening response (CAR), overall morning cortisol levels, change in the cortisol levels during the day, and bedtime cortisol levels). In addition, they completed the SF-36 questionnaire to obtain a measure of HRQoL (i.e. reflecting physical and mental functional health status). Results showed that higher awakening and bedtime cortisol levels and the CAR were associated with a better perception of both physical and mental health. In addition, the wake-to-bed cortisol slope was only positively related to physical health. No sex differences were found. These findings suggest that the awakening and bedtime cortisol levels and the CAR are the most relevant indices of diurnal cortisol secretion for understanding the relationship between HPA-axis functioning and HRQoL status in older people.

An inverted U-shaped relationship between cortisol awakening response and same-day error monitoring function in healthy males

The cortisol awakening response (CAR) is thought to provide an energetic "boost" for the coming day and has been shown to be associated with prefrontal dependent function. The aim of the current study was to examine the relationship between the CAR and same-day neural activity following an error response task. Forty-six healthy males (22.25 years ± 1.98) collected saliva samples at 0, 30 and 45 min post-awakening to measure the CAR, and on the same afternoon event-related potential activity during error processing was measured. Although no association was observed between CAR and post-error behavior, a significant quadratic relationship was observed between CAR and Error-related Negativity (ERN) amplitude, and this association remained while controlling for confounding factors. This finding suggested the existence of an inverted U-shaped relationship between CAR and the same-day error-monitoring function in healthy males.

Cortisol reactivity to a psychosocial stressor significantly increases the risk of developing Cognitive Impairment no Dementia five years later

Alzheimer's disease (AD) patients show high cortisol levels suggesting that biological mediators of stress may play a role in the neurodegenerative process of cognitive disorders. However, there is no consensus as to whether cortisol concentrations represent a risk factor for the development of cognitive impairment. We analyzed the potential association between the incidence of cognitive impairment and cortisol concentrations under basal and acute stress conditions in 129 individuals aged 50 years or older, with preserved cognitive and functional abilities. All participants were recruited in 2011 for assessment of cognitive performance and cortisol levels. Cortisol was analyzed in saliva samples collected during two typical and consecutive days, in the morning, afternoon, and night, and also during exposure to an acute psychosocial stressor (Trier Social Stress Test - TSST). After a five-year follow-up, 69 of these volunteers were reassessed for cognitive performance, functional evaluation, memory complaints, and depression. The incidence of cognitive impairment not dementia (CIND) was 26.1 %, and was positively associated with greater TSST-induced cortisol release (responsiveness) [(95 % CI = 1.001-1.011; B = 0.006), p = 0.023]. Moreover, five years before diagnosis, participants who later developed CIND had greater responsiveness to TSST (p = 0.019) and lower cortisol awakening response (CAR: p = 0.018), as compared to those who did not develop CIND. These findings suggest that higher psychosocial stress responsiveness profiles may represent a preclinical sign of cognitive impairment.

Stress, the cortisol awakening response and cognitive function

There is evidence that stress-induced disruption of the circadian rhythm of cortisol secretion, has negative consequences for brain health. The cortisol awakening response (CAR) is the most prominent and dynamic aspect of this rhythm. It has complex regulatory mechanisms making it distinct from the rest of the cortisol circadian rhythm, and is frequently investigated as a biomarker of stress and potential intermediary between stress and impaired brain function. Despite this, the precise function of the CAR within the healthy cortisol circadian rhythm remains poorly understood. Cortisol is a powerful hormone known to influence cognition in multiple and complex ways. Studies of the CAR and cognitive function have used varied methodological approaches which have produced similarly varied findings. The present review considers the accumulating evidence linking stress, attenuation of the CAR and reduced cognitive function, and seeks to contextualize the many findings to study populations, cognitive measures, and CAR methodologies employed. Associations between the CAR and both memory and executive functions are discussed in relation to its potential role as a neuroendocrine time of day signal that synchronizes peripheral clocks throughout the brain to enable optimum function, and recommendations for future research are provided.

Relationship between Cortisol Changes during the Night and Subjective and Objective Sleep Quality in Healthy Older People

The aim of this study was to investigate whether the nighttime cortisol release was associated with subjective and objective sleep quality and the discrepancy between them. Forty-five healthy older adults (age range from 56 to 75 years) collected salivary samples immediately before sleep and immediately after awakening on two consecutive nights. Actigraphy was used to assess objective sleep quality and quantity. A sleep diary was used to assess subjective sleep quality. Linear mixed models were performed using subjective and objective sleep quality data from 76 nights to investigate between-subject associations. We observed that larger changes in cortisol levels between sleep onset and awakening, reflecting a healthier circadian rhythm of the Hypothalamic-Pituitary-Adrenal (HPA) axis, were associated with better subjective sleep quality, but not with objective sleep quality. Moreover, smaller changes in nighttime cortisol were associated with lower subjective sleep quality relative to objective sleep quality. All these results were observed even after controlling for important confounders such as sleep quantity, age, sex, subjective socioeconomic status, stress perception, depression, physical activity, and adherence to the salivary sampling protocol. This study demonstrates that subjective sleep quality in older people may be explained, to some extent, by the activity of the HPA axis.

The effects of stress on cardiovascular disease and Alzheimer's disease: Physical exercise as a counteract measure

AD is a complicated multi-systemic neurological disorder that involves different biological pathways. Several risk factors have been identified, including chronic stress. Chronic stress produces an alteration in the activity of the hypothalamic pituitary adrenal (HPA) system, and the autonomic nervous system (ANS), which over time increase the risk of AD and also the incidence of cardiovascular disease (CVD) and risk factors, such as hypertension, obesity and type 2 diabetes, associated with cognitive impairment and AD. Considering the multi-factorial etiology of AD, understanding the complex interrelationships between different risk factors is of potential interest for designing adequate strategies for preventing, delaying the onset or slowing down the progression of this devastating disease. Thus, in this review we will explore the general mechanisms and evidence linking stress, cardiovascular disease and AD, and discuss the potential benefits of physical activity for AD by counteracting the negative effects of chronic stress, CVD and risk factors.

The relationship between loneliness and cognition in healthy older men and women: The role of cortisol

Loneliness has been associated with an increased risk of cognitive decline and dementia in older people, as well as a dysregulation of Hypothalamic-Pituitary-Adrenal (HPA) axis functioning. In addition, it has been suggested that women are more vulnerable to the negative effects of loneliness on health. Our aim was to analyze the effect of HPA-axis functioning as a mediator in the relationship between loneliness and cognitive function, and interactions depending on sex, in healthy older people. To do so, 86 healthy older people (52.3% female) from 60 to 80 years old (M = 67.44, SD = 4.37) completed the revised UCLA loneliness scale. A neuropsychological battery was administered to assess global cognition, processing speed, attention and executive function, working memory, and verbal memory immediate and delayed recall. Saliva samples were provided on two consecutive weekdays to obtain awakening and bedtime cortisol levels, the diurnal cortisol slope (DCS), and the area under the curve with respect to the ground (AUCg). Our results showed that loneliness was not directly associated with cognitive performance. Furthermore, loneliness was related to higher bedtime cortisol levels, but not to awakening cortisol, the DCS, or the AUCg. In addition, loneliness was associated with worse performance on attention and processing speed, executive function, and verbal memory immediate recall, via bedtime cortisol levels. Therefore, we suggest that HPA-axis functioning is one of the biological mechanisms that mediate the relationship between loneliness and poorer cognitive function. No sex differences were observed in these associations.

Apolipoprotein E gene polymorphism, posttraumatic stress disorder, and cognitive function in older U.S. veterans: Results from the National Health and Resilience in Veterans Study

BACKGROUND

Although the ε4 allele of the apolipoprotein E (APOE) gene and posttraumatic stress disorder (PTSD) have been linked to cognitive dysfunction and dementia risk, it is unknown whether they interact to predict cognitive dysfunction.

METHODS

We analyzed data from European-American (EA) veterans who participated in the National Health and Resilience in Veterans Study (NHRVS): main sample (n = 1,386) and primary replication sample (n = 509). EAs from the Yale-Penn Study cohort (n = 948) served as a second replication sample. Multivariable analyses were conducted to evaluate the predictive effects of ε4 carrier status and PTSD on cognitive functioning, with a focus on whether PTSD moderates the effect of ε4 carrier status.

RESULTS

APOE ε4 allele carrier status (d = 0.15 and 0.17 in the main and primary replication NHRVS samples, respectively) and PTSD (d = 0.31 and 0.17, respectively) were independently associated with lower cognitive functioning. ε4 carriers with PTSD scored lower than those without PTSD (d = 0.68 and 1.29, respectively) with the most pronounced differences in executive function (d's = 0.75-1.50) and attention/concentration (d's = 0.62-1.33). A significant interaction was also observed in the Yale-Penn sample, with ε4 carriers with PTSD making more perseverative errors on a measure of executive function than those without PTSD (24.7% vs. 17.6%; d = 0.59).

CONCLUSIONS

APOE ε4 allele carriers with PTSD have substantially greater cognitive difficulties than ε4 carriers without PTSD. These results underscore the importance of assessing, monitoring, and treating PTSD in trauma-affected individuals who are at genetic risk for cognitive decline and dementia.

Odorants: a tool to provide nonpharmacological intervention to reduce anxiety during normal and pathological aging

Anxiety disorders represent 1 of the most common classes of psychiatric disorders. In the aging population and for patients with age-related pathology, the percentage of people suffering of anxiety is significantly elevated. Furthermore, anxiety carries with it an increased risk for a variety of age-related medical conditions, including cardiovascular disease, stroke, cognitive decline, and increased severity of motor symptoms in Parkinson's disease. A variety of anxiolytic compounds are available but often carry with them disturbing side effects that impact quality of life. Among nonmedicinal approaches to reducing anxiety, odor diffusion and aromatherapy are the most popular. In this review, we highlight the emerging perspective that the use of odorants may reduce anxiety symptoms or at least potentiate the effect of other anxiolytic approaches and may serve as an alternative form of therapy to deal with anxiety symptoms. Such approaches may be particularly beneficial in aging populations with elevated risk for these disorders. We also discuss potential neural mechanisms underlying the anxiolytic effects of odorants based on work in animal models.

Age differences in the relationship between cortisol and emotional memory

Research has shown that remembering emotional information can occur at the expense of surrounding neutral background information; this emotional memory trade-off occurs similarly in both younger and older adults. We investigated how levels of cortisol, a hormone that acts on the central nervous system, impact emotional memory with age. Younger and older adult participants incidentally encoded emotional (positive, negative, or neutral) items placed on neutral backgrounds and later completed recognition tests for both the items and the backgrounds. Cortisol was measured at multiple time points to assess basal cortisol. Results are reported for prelearning levels, as findings were comparable across time points. Results revealed that higher levels of cortisol predicted a lower memory trade-off effect for older adults compared to younger adults and that this age difference in the role of cortisol tended to be strongest for memory for negative items (rather than for backgrounds or neutral items). No such interaction emerged for the positive trade-off effect. These results suggest that cortisol levels play a different role in supporting emotional memory across the life span, with lower levels of cortisol potentially more adaptive for memory for negative emotional information and higher levels indicating potential impairment with age. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Exercise, the diurnal cycle of cortisol and cognitive impairment in older adults

Exercise has been shown to reduce the risk of developing Mild Cognitive Impairment and Alzheimer's disease as well as to improve cognition in healthy and cognitively impaired individuals. However, the mechanisms of these benefits are not well understood. The stress hypothesis suggests that the cognitive benefits attributed to exercise may partially be mediated by changes in the cortisol secretion pattern. Chronic stress may increase the risk of AD and exacerbate the cognitive deficits and brain pathology characteristic of the condition while physical activity has been shown to attenuate most of stress consequences and risk factors for AD. Initially, research on the effects of cortisol on cognition and physical activity focused on cortisol levels at one time point but the circadian pattern of cortisol secretion is complex and it is still unclear which aspects are most closely associated with cognitive function. Thus, the aim of this review was to analyze the exercise/stress/cognition hypothesis focusing on the effects of the diurnal cycle of cortisol on cognitive function and physical activity in older adults with and without cognitive impairment.

The cortisol awakening response predicts response inhibition in the afternoon of the same day

The cortisol awakening response (CAR) is the rapid increase of cortisol levels 30-45 min after awakening in the morning. Numerous studies have indicated the relationship between the CAR and cognition. However, little is known about daily variation in the CAR and cognitive function in healthy adults. The aim of the present study was to investigate whether the CAR predicted the response inhibition function on the same day in both behaviour and the dynamic time course of brain processing. The saliva samples of 47 healthy men were collected at three time points: immediately on awakening, 30 min and 45 min post-awakening in the morning. Participants performed a Go/NoGo task while electroencephalograms (EEG) were recorded in the afternoon of the same day. The results showed that a greater CAR was associated with a stronger N2. In the sub-group of CAR responders (n = 33) the CAR was negatively related to the false alarm rate of NoGo-trials. Our findings suggested that the CAR was predictive of the function of response inhibition in both the earlier cognitive step (i.e., conflict monitoring) and the behavioural performance of response inhibition on the same day in healthy men.

Elevated cortisol awakening response associated with early life stress and impaired executive function in healthy adult males

Experiencing early life stress (ELS) and subsequent dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis may play a role in the aetiology of mental health disorders. However, the exact mechanisms linking HPA-axis dysregulation with the development of psychopathology have not been fully delineated. Progress in this area is hampered by the complex and often conflicting associations found between markers of HPA-axis function and risk factors for mental health disorders such as impaired executive function (EF) and ELS. This study investigated the association of the cortisol awakening response (CAR) with ELS and EF in a healthy adult male population (n=109, aged 21-63). As previous inconsistencies in CAR and ELS association studies may be the result of not considering ELS-related factors such as cumulative exposure, type of stressor and developmental timing of ELS, these were also investigated. The main findings were that the CAR was significantly elevated in individuals reporting ELS compared to those reporting no ELS (p=0.007) and that an elevated CAR predicted poorer problem solving/planning (p=0.046). Cumulative exposure, type of stressor and developmental timing of ELS were also found to impact significantly on the CAR. These results suggest that ELS is associated with chronic changes in HPA-axis function and that these changes may be associated with impairments in problem solving/planning. Future work should investigate further the neurobiological mechanisms linking ELS, the CAR and EF and their role in conferring risk for the development of mental health disorders.

Slow wave sleep and accelerated forgetting

We investigated whether the benefit of slow wave sleep (SWS) for memory consolidation typically observed in healthy individuals is disrupted in people with accelerated long-term forgetting (ALF) due to epilepsy. SWS is thought to play an active role in declarative memory in healthy individuals and, furthermore, electrographic epileptiform activity is often more prevalent during SWS than during wakefulness or other sleep stages. We studied the relationship between SWS and the benefit of sleep for memory retention using a word-pair associates task. In both the ALF and the healthy control groups, sleep conferred a memory benefit. However, the relationship between the amount of SWS and sleep-related memory benefits differed significantly between the groups. In healthy participants, the amount of SWS correlated positively with sleep-related memory benefits. In stark contrast, the more SWS, the smaller the sleep-related memory benefit in the ALF group. Therefore, contrary to its role in healthy people, SWS-associated brain activity appears to be deleterious for memory in patients with ALF.