title: Pushing the Limits: Chronotype and Time of Day Modulate Working Memory-Dependent Cerebral Activity.
abstract: Morning-type individuals experience more difficulties to maintain optimal attentional performance throughout a normal waking day than evening types. However, time-of-day modulations may differ across cognitive domains. Using functional magnetic resonance imaging (fMRI), we investigated how chronotype and time of day interact with working memory at different levels of cognitive load/complexity in a N-back paradigm (N0-, N2-, and N3-back levels). Extreme morning- and evening-type individuals underwent two fMRI sessions during N-back performance, one 1.5 h (morning) and one 10.5 h (evening) after wake-up time scheduled according to their habitual sleep-wake preference. At the behavioral level, increasing working memory load resulted in lower accuracy while chronotype and time of day only exerted a marginal impact on performance. Analyses of neuroimaging data disclosed an interaction between chronotype, time of day, and the modulation of cerebral activity by working memory load in the thalamus and in the middle frontal cortex. In the subjective evening hours, evening types exhibited higher thalamic activity than morning types at the highest working memory load condition only (N3-back). Conversely, morning-type individuals exhibited higher activity than evening-type participants in the middle frontal gyrus during the morning session in the N3-back condition. Our data emphasize interindividual differences in time-of-day preferences and underlying cerebral activity, which should be taken into account when investigating vigilance state effects in task-related brain activity. These results support the hypothesis that higher task complexity leads to a chronotype-dependent increase in thalamic and frontal brain activity, permitting stabilization of working memory performance across the day.
authors.affiliation: Cyclotron Research Centre, University of Liège , Liège , Belgium ; Neuropsychology Unit, University of Liège , Liège , Belgium.
authors.forename: Christina
authors.initials: C
authors.lastname: Schmidt
authors.affiliation: Cyclotron Research Centre, University of Liège , Liège , Belgium ; Neuropsychology Unit, University of Liège , Liège , Belgium.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Collette
authors.affiliation: Centre for Chronobiology, Psychiatric Hospital of the University of Basel , Basel , Switzerland.
authors.forename: Carolin F
authors.initials: CF
authors.lastname: Reichert
authors.affiliation: Centre for Chronobiology, Psychiatric Hospital of the University of Basel , Basel , Switzerland.
authors.forename: Micheline
authors.initials: M
authors.lastname: Maire
authors.affiliation: Cyclotron Research Centre, University of Liège , Liège , Belgium ; Neuropsychology Unit, University of Liège , Liège , Belgium.
authors.forename: Gilles
authors.initials: G
authors.lastname: Vandewalle
authors.affiliation: UR2NF - Neuropsychology and Functional Neuroimaging Research Unit affiliated at CRCN - Center for Research in Cognition and Neurosciences, Neurosciences Institute, Université Libre de Bruxelles , Brussels , Belgium.
authors.forename: Philippe
authors.initials: P
authors.lastname: Peigneux
authors.affiliation: Centre for Chronobiology, Psychiatric Hospital of the University of Basel , Basel , Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Cajochen
keywords: BOLD activity; chronotype; task complexity; time of day; working memory