A longitudinal study of basal cortisol in infants: Intra-individual variability, circadian rhythm and developmental trends

Mothers with normally developing babies were visited in their homes during 13 consecutive weeks, when the babies were around 5–8 months of age. Basal salival cortisol measures were taken for both the baby and the mother on arrival.The infants’ basal cortisol decreased linearly with age, was negatively related to sleep, and did not show adult-like circadian declines from morning to mid-afternoon. Furthermore, while the infants showed relative stability across individuals, they displayed great intra-individual variability across assessments. Contrarily, the mothers displayed important inter-individual variability, together with a relative stability across assessments. The infants’ important intra-individual variability was not affected by gender, nor time of visit, nor was it related to the mothers’ basal cortisol. Daily measures of basal cortisol taken in a subgroup of infants indicated the day-to-day intra-individual variability to be of the same magnitude as the week-to-week variability.The question of how the intra-individual variability in basal cortisol affects assessments of cortisol in infancy is addressed. The aggregation of data with the goal of increasing the reliability of the assessments is shown to be inadequate for infant basal cortisol.     

The relationship between morningness–eveningness, time-of-day, speed of information processing, and intelligence

Morningness–Eveningness refers to individual differences in circadian phase position of spontaneous sleep–wake rhythms and to subject alertness. There is some evidence indicating that performance on cognitive tasks may be influenced by Morningness–Eveningness and time-of-day. Given the potential importance of such a finding for the assessment of cognitive ability we conducted a study assessing the relationship between Morningness–Eveningness, time-of-day, and performance on the Multidimensional Aptitude Battery IQ (MAB-IQ) and Inspection Time (IT) task. Twenty male and 50 female participants classified according to their scores on the Morningness–Eveningness dimension (Horne & Östberg, 1976) were administered the MAB and IT tasks in the morning (0900 h) and in the late afternoon (1500 h). No significant effect of time of testing, and Morningness–Eveningness was observed except for the Spatial subtest of the MAB. Morning Type-participants performed significantly worse in the morning session in Spatial subtest and better in the late afternoon session and Evening Type-participants performed significantly better in the morning than in the late afternoon session. These results do not support the hypothesis that there is a reliable relationship between Morningness–Eveningness, time-of-day and cognitive ability.     

Refining the psychometric properties of the circadian type inventory

The psychometric properties of the 18-item circadian type inventory (CTI) were examined in a non-shiftwork sample. Inter-item correlations for each scale were low to moderate. Confirmatory factor analysis (CFA) via structural equation modelling did not support the posited structure of the CTI. Principal components analysis and reliability analyses suggested the CTI is better represented by 11-items. The revised five item FR scale accounted for 27% of the variance, had stronger factor loadings and increased Cronbach alpha. The psychometric properties of the six item LV scale were marginally improved and explained 21% of the variance. The two-factor 11-item model was supported by CFA. Compared to the 18-item model, the 11-item model showed a marked improvement on several incremental fit indices and achieved a more parsimonious model fit. There was some indication of gender differences but a multi-group CFA indicated model parsimony was best for the invariant model. Gender difference needs to be further examined in large samples using a similar gender balance. It is concluded that the 11-item CTI is psychometrically superior to the original. However, its predictive efficacy needs to be examined in longitudinal studies.     

Examining the sex- and circadian dependency of a learning phenotype in mice with glycine transporter 1 deletion in two Pavlovian conditioning paradigms

Behavioural characterisation of transgenic mice has been instrumental in search of therapeutic targets for the modulation of cognitive function. However, little effort has been devoted to phenotypic characterisation across environmental conditions and genomic differences such as sex and strain, which is essential to translational research. The present study is an effort in this direction. It scrutinised the stability and robustness of the phenotype of enhanced Pavlovian conditioning reported in mice with forebrain neuronal deletion of glycine transporter 1 by evaluating the possible presence of sex and circadian dependency, and its consistency across aversive and appetitive conditioning paradigms. The Pavlovian phenotype was essentially unaffected by the time of testing between the two circadian phases, but it was modified by sex in both conditioning paradigms. We observed that the effect size of the phenotype was strongest in female mice tested during the dark phase in the aversive paradigm. Critically, the presence of the phenotype in female mutants was accompanied by an increase in resistance to extinction. Similarly, enhanced conditioned responding once again emerged solely in female mutants in the appetitive conditioning experiment, which was again associated with an increased resistance to extinction across days, but male mutants exhibited an opposite trend towards facilitation of extinction. The present study has thus added hitherto unknown qualifications and specifications of a previously reported memory enhancing phenotype in this mouse line by identifying the determinants of the magnitude and direction of the expressed phenotype. This in-depth comparative approach is of value to the interpretation of behavioural findings in general.     

Preliminary evidence of diurnal rhythms in everyday behaviors associated with positive affect

The authors used the Electronically Activated Recorder (EAR) to track within-day variability in everyday behaviors associated with positive and negative affect across two samples. The EAR is a portable audio recorder that periodically samples snippets of ambient sounds from participants’ momentary environments. The recorded sounds are then coded for different behaviors. The study tested whether previous findings regarding diurnal patterns in self-reported mood extend to naturalistically observed behavior. Across both samples, behavior associated with positive affect (i.e., socializing, laughing, and singing) varied according to a sinusoidal 24-h rhythm centered around participants’ average waketime while behavior associated with negative affect (i.e., arguing and sighing) did not. Further, there was preliminary evidence that personality traits can moderate these rhythms (e.g., their amplitude).     

Thinking about complex decisions: How sleep and time-of-day influence complex choices

In this study, we systematically manipulate a person’s state of sleep; Sleep-deprived and Well-rested along with Matching or Mismatching the decision time-of-day to their circadian preferred time-of-day. We assessed how these conditions influenced performance on an incentivized complex decision task. In the overall analysis of these variables no differences emerged. However, a comparison of the more cognitively depleting Sleep-deprivation/Circadian-mismatch condition to the cognitively enhancing Well-rested/Circadian-match condition showed improved performance in the Well-rested/Circadian matched group for one complex decision task but not for the other. These findings build upon the existing literature on sleep and circadian rhythm effects while uniquely observing the combined effects of these variables on complex decision making.     

Predicting students’ learning strategies: The contribution of chronotype over personality

Students’ learning strategies as well as the search for its determinants have gained expanding interest in psychology and educational research. The present study investigated the contribution of chronotype, another construct of increasing importance in the academic context, to students’ learning strategies controlling for the established predictor of personality and its relations to chronotype. A sample of 318 college students (mean age = 22.6, SD = 2.5; age range = 19–34) was assessed online through self-report questionnaires. We discriminated between two learning strategy factors aggregated by a diverse set of learning strategies, learning discipline and elaboration. First, results confirmed significant associations between most personality scales and students’ strategy use. Furthermore, we found evidence for significant associations between chronotype and personality, as well as chronotype and learning strategies. Finally, structural equation modeling revealed that openness, agreeableness, conscientiousness, and morningness were significant predictors for elaboration, whereas learning discipline was significantly predicted by conscientiousness and morningness. We conclude that chronotype plays an important role explaining students’ learning strategies over and above personality.