The cortisol awakening response (CAR) and post awakening melatonin secretion
We are exploring the relationship between the CAR and melatonin secretion (measured in saliva) in the first 45 minutes post awakening. Melatonin and cortisol secretion are closely related and the role of melatonin in predicting psychological indices, known to be associated with the CAR, has not yet been explored. For example, as melatonin is associated with somnolence we predict melatonin secretion may be associated with indices of fatigue. Data collection is currently underway.
The cortisol awakening response (CAR) and balance
We are exploring association between the CAR and postural sway. Using a within and between-subject design we are exploring whether the CAR predicts postural sway in the afternoon of the same day. In particular we are examining the impact of visual dependency on postural sway.
The cortisol awakening response (CAR) and brain plasticity
Using rapid transcranial magnetic stimulation (rTMS) to induce brain plasticity in the motor cortex we have demonstrated, in a within-subject study design of healthy young participants, that the size of the CAR predicts capacity to induce neural plasticity. We are currently exploring whether between-subject differences in trait CAR predict trait differences in brain plasticity, eg in adolescents born pre-term. This work is undertaken in collaboration Mike Ridding and Julia Pitcher at the University of Adelaide.
The cortisol awakening response (CAR) and sleep inertia
Using an intensive case-study design of a healthy young male over 50 study days we are exploring associations between day-differences in the CAR and day differences in arousal and mood in the immediate post awakening period. Emerging data suggest that the dynamics and timing of the CAR are linked with indices of post awakening arousal, in contrast the total amount of cortisol secreted (especially after the peak) are associated with mood.
We are also examining predictors of the CAR from prior day experiences and behaviour (drinking and exercise).
Measurement of the cortisol awakening response (CAR)
Using a combination of wrist-worn activity meters to determine time of awakening and MEMS monitoring of saliva sapling times we are investigating the impact of imprecise saliva sampling on measurement of the CAR.
We have found that delays between awakening and collection of the first sample of between 5-15 minutes results in erroneous overestimation of the CAR as well as earlier timing of the peak. This has led us to explore the CAR at five-minute intervals post awakening which revealed a lag of about 10 minutes from the point of awakening until initiation of the cortisol rise.
We are currently exploring the prevalence of non-CAR events across individuals and days.
The impact of glaucoma on the cortisol awakening response (CAR) and mood
We are investigating whether reduced retinal sensitivity in open angled glaucoma is associated with an attenuated CAR and poor psychological well-being. In association with the International Glaucoma Association we have recruited volunteers, and matched control participates, to examine the CAR in this population. Data collection is currently underway.
The psychophysiology of human attachment style
Previous work has examined diurnal patterns of cortisol secretion in relation to attachment style. We are now exploring how attachment style moderates stress responding. Using the group Trier Social Stress Test (gTSST) we are examining the interaction between attachment style, social interaction and stress responding.
The usefulness of patterns of cortisol secretion as a biomarker of well-being in healthy young participants
We have used an intensive four-day study design, including strict monitoring of participant adherence to the requested saliva sampling protocol as well as comprehensive assessment of trait and stat well-being and ill-being, to explore the usefulness of cortisol as a biomarker of psychological status in healthy young females.
We have found that no aspect of the diurnal pattern of salivary cortisol secretion (the CAR or day decline) is associated with indices of either trait or state well-being or ill-being. We have interpreted this in terms of neurotoxicity hypothesis of HPA axis function, where healthy young participants can show resilience to the negative impact of psychological distress. In contrast, older people, having been exposed to more prolonged periods of life events, are more likely to show dysfunctional HPA axis function (ie neurotoxicity), measureable by aberrant patterns of cortisol secretion.
Hair cortisol concentration and well-being in the healthy young and healthy old
As a follow-up to our work showing no relationship between diurnal patterns of cortisol, measured in saliva, in healthy young females we have explored hair cortisol concentrations in the healthy young compared to the healthy old. These analyses are underway.