Chronotype and synchrony effects in human cognitive performance: a systematic review

Chronotype is a proxy for various intra-individual rhythms (e.g. sleep-wake cycles) which fluctuate throughout the day. The extent to which chronotype modulates cognitive performance remains unclear. Here, we systematically reviewed studies to determine the influence of chronotype on its own, and/or in interaction with time of day (ToD; optimal/non-optimal), in cognitive function in healthy adults. Following PRISMA guidelines, data searches were conducted in PubMed and Web of Science databases (11 March 2024), yielding 65 studies (53 in adults aged 18–45 y; 11 comparing adults aged 18–32 and 50–95 y; one involving only morning type adults aged 60–76 y). Most of the reviewed studies (>80%) indicated no main effect of chronotype on cognitive function. There was evidence from 29 (45.31%) of 64 studies involving adults aged 18–45 y of a synchrony effect (i.e. superior performance at optimal ToD) in morning and/or evening types, mostly in attention, inhibition, and memory. In older adults, there was evidence of a synchrony effect from 10 (83.33%) of 12 studies, especially on tasks involving fluid abilities. Limited evidence suggested higher activation of inhibition-related brain regions at optimal ToD in both chronotypes, and synchrony effects being impacted by certain exogenous factors known to affect arousal and performance (e.g. task complexity, lighting conditions). Our findings highlight the need to carefully consider age along with endogenous and exogenous sources of intra-individual variations in arousal while determining synchrony effect in cognitive functions. Not acknowledging these synchrony effects may also result in exaggerated cognitive deficits especially in the elderly.