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Abstract
Although peaks and troughs in cognitive performance characterize our daily functioning, time-of-day fluctuations remain marginally considered in the domain of cognitive psychology and neuropsychology. Here, we attempt to summarize studies looking at the effects of sleep pressure, circadian variations, and chronotype on cognitive functioning in healthy subjects. The picture that emerges from this assessment is that beyond physiological variables, time-of-day modulations affect performance on a wide range of cognitive tasks measuring attentional capacities, executive functioning, and memory. These performance fluctuations are also contingent upon the chronotype, which reflects interindividual differences in circadian preference, and particularly upon the synchronicity between the individuals' peak periods of circadian arousal and the time of the day at which testing occurs. In themselves, these conclusions should direct both the clinician's and the researcher's attention towards the utmost importance to account for time-of-day parameters when assessing cognitive performance in patients and healthy volunteers.
We thank K. Blatter and three anonymous reviewers for helpful comments on previous versions of this manuscript. CS is supported by the Lundbeck-Belgian College of Neuropharmacology and Biological Psychiatry and by the Belgian National Foundation of Scientific Research (FNRS). FC is supported by the FNRS. PP was formerly supported by the PAI/IAP Interuniversity Pole of Attraction P5/04. CC is supported by grants from the Swiss National Foundation START Grants 3130–054991 and 3100–055385.98.