• chronotype
• cognition
• ruminations
• sleep

This research explores the association between chronotype (individual differences in circadian rhythms) and ruminative thought patterns in healthy subjects. This research also evaluates factors that could influence that association, such as executive function performance (such as cognitive flexibility, inhibitory control, and attentional switching) as well as sleep disturbances.
Objectives: There is an association, validated by previous studies, between chronotype and depression, particularly with one of the symptoms of depression: rumination. In fact, evening chronotypes show a higher degree of rumination as compared to morning ones. The purpose of this thesis is to evaluate whether the association between chronotype and rumination can be influenced by executive function performance or sleep quality disturbances. Specific Objective 1: Assess the association between chronotype and rumination. Specific Objective 2: Evaluate whether executive function performance (cognitive flexibility, inhibitory control, attentional switching) may influence the association between chronotype and rumination. Specific Objective 3: Investigate whether sleep quality disturbances may influence the association between chronotype and rumination.
Methods: This is an Observational, Cross-sectional, Prospective study conducted as part of a research carried out by the SonnoLab at the Institute of Physiology (University of Pisa). The study sample consists of 236 subjects selected from the general population, including 99 male and 137 female. They are healthy volunteers with negative psychiatric or neurological history.
Participants were evaluated through computer-based cognitive tests such as the Wisconsin Card Sorting Test, the Stroop Task and the Task switching and through questionnaires, including the reduced version of the Morningness-Eveningness Questionnaire (rMEQ), the Pittsburgh Sleep Quality Index (PSQI) and the Ruminative Response Scale (RRS). Moreover, the sleep-activity patterns of each subject was monitored for 4 to 8 days using actigraphy to allow the assessment of various parameters including the total sleep time (TST), sleep efficiency (SE), waking after sleep onset (WASO), sleep regularity index (SRI), mid-sleep point and the sleep timing (sleep onset and sleep offset).
Results: Participants were classified according to chronotype using the rMEQ, resulting that the sample was composed of 64% Neither type, 20% Morning Type and 16% Evening Type.
Results of objective 1: Chronotype groups showed significant differences only in the subscale related to depression (Depression Related Rumination). The group classified as Evening Type exhibited more Depression Related Rumination with a significantly higher score (median = 27.50, IQR = 19.00, 34.00) compared to both Neither (median=22.00, IQR = 17.00, 28.00) and Morning Types (median = 23.00, IQR = 18.00, 27.00). It was also confirmed a correlation between the Depression Related Subscale and the rMEQ (rho = -0.16, p-value = 0.016), with higher RRS scores correlated to lower rMEQ scores. The association between Depression Related Rumination and Chronotype remains significant (p-value = 0.022) also when adjusting for age, sex, and alcohol consumption.
Results of objective 2: Regarding Cognitive variables only in the WCST correct answers variable (the total number of correct answers), was observed a worse score in the Evening Type group (median = 61.00, IQR = 52.50, 64.50) comparing with Neither (median = 65.00, IQR = 55.00, 75.25) and Morning Type (median = 65.00, IQR = 61.00, 75.00) groups. However, multivariate regression analysis did not show a significative effect of the WCST correct answers in the association between Depression related Ruminations and Chronotype.
Results of obiective 3: The Evening Type group exhibited significantly worse sleep quality, both as measured by the Pittsburgh Sleep Quality Index (PSQI) and when considering actigraphic parameters such as SE and WASO. Nevertheless, only the sleep quality as measured through the PSQI showed an effect on the association between Evening chtonotype and Depression Related ruminations, specifically, when the PSQI was included to the multivariate regression model, the chronotype was no longer significantly associated with the Depression Related Ruminations, while the PSQI was significantly associated, with lower sleep quality being associated with higher Depression Related ruminations.
In conclusion, our study aimed to explore the association between rumination and chronotype. According to our results, Evening chronotype was associated with a tendency to higher “Depressive-Related Ruminations” and higher ruminations scores were correlated with poorer sleep quality as measured by the PSQI. Sleep quality seems to mediate the relationship between being an Evening chronotype and a tendency toward depressive rumination: individuals with an evening chronotype and poor sleep quality are more predisposed to ruminate. We analyzed cognitive aspects too: although individuals with an Evening chronotype exhibit lower cognitive flexibility, cognitive flexibility itself does not appear to be associated with rumination.
Results of this study highlight the potential protective role of good sleep quality in contributing to reduce rumination and, consequently, to reduce mental health disturbances, especially in individuals with an Evening chronotype.