Early Birds, Night Owls and Working Memory

There is a growing body of research showing the individual preference for mornings or evenings influences human performance and disease.

Early birds is common term for individuals who arise early and prefer activity in mornings. Night owls often stay up late at night and find they are more productive in the evenings.

This day time preference pattern is known scientifically as chronotype.

Christina Schmidt and colleagues from Belgium recently published an interesting study of the effect of chronotype on working memory and brain activity.

The key elements of their research design included the following elements:

• Subjects: 32 young healthy volunteers with 16 showing a morning chronotype and 16 showing a evening chronotype
• Procedures: Subjects participated in a series of studies involving sleep diaries, polysomnography in a sleep lab and neuropsychological testing. Working memory was tested using a procedure known as the N-Back Paradigm.
• Brain imaging: Subjects completed functional magnetic resonance imaging in a 3T MRI scanner. Brain regional patterns of activation were analyzed during working memory tasks. Individual performance and activation patterns were compared between a morning scan and and evening scan.  Morning preference individuals were compared to evening preference individuals.

The main findings from the study included the following:

• Subjects performed modestly better on the most complex working memory task based on their chronotype--morning individuals performed better in the morning and evening individuals performed better in the evening
• During evening imaging, evening preference individuals demonstrated higher memory task activation of the brain thalamus than morning preference individuals
• During morning imaging, morning preference individuals demonstrated higher memory task activation of the middle frontal gyrus than evening preference individuals

The authors note that one implication of their study is the need to measure chronotype preference in neuropsychological testing and functional brain imaging. Chronotype preference is a potential confounding variable in memory and other cognition studies.

Additionally, this study shows that brain correlates of peak performance do appear to depend on time of day. Morning preference types appear to perform best in the morning and might want to arrange their most demanding cognitive tasks in the morning. The opposite is true for evening chronotypes.

So for example, if you are an evening chronotype, you might want to consider taking a memory-intensive task, i.e. the SAT exam as late in the day as possible.

Individuals with more interest in this study can access the free full-text manuscript by clicking on the PMID link in the citation below.

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Schmidt C, Collette F, Reichert CF, Maire M, Vandewalle G, Peigneux P, & Cajochen C (2015). Pushing the Limits: Chronotype and Time of Day Modulate Working Memory-Dependent Cerebral Activity. Frontiers in neurology, 6 PMID: 26441819