Does the Season Change How Well People Think?
The study everyone quotes for a September peak measured brain activity, not performance, and found performance did not move at all.
Reviewed against primary sources on September 8, 2026 by the Soon operations research team. How we vet the evidence
The evidence in one line
In 28 young adults kept for several days without seasonal cues, performance on attention and working-memory tasks stayed stable across the year while the brain activity supporting those tasks varied by season, peaking at different points for each task (Meyer et al., 2016). Separately, across 3,353 older adults, cognition was higher in summer and autumn than in winter and spring by an amount equivalent to 4.8 years of age difference (Lim et al., 2018). Age and measurement method, not the calendar alone, decide which of those findings applies.
What the widely quoted study actually measured
The claim that sustained attention peaks near the summer solstice and working memory near the autumn equinox comes from a single fMRI study of 28 healthy young adults, each kept for four and a half days in an environment stripped of seasonal cues before testing (Meyer et al., 2016). Both statements are about brain responses. They describe where in the year the measured neural activity supporting each task reached its maximum, and the two tasks peaked at different points.
Performance did not follow. The authors report that responses on the attention task were not related to significant changes in performance, which remained good and stable throughout the year. The finding is about the cerebral resources recruited to hold performance steady, which is a real and interesting result, and a different result from the one usually attributed to it. A schedule built on the belief that staff think measurably better in September is built on a claim the study did not make.
Where seasonal differences in performance do show up
A much larger analysis found seasonal variation in cognition itself. Across five observational cohorts totalling 3,353 older adults, average composite cognitive function was higher in summer and autumn than in winter and spring, a difference equivalent in effect to 4.8 years of age (95% CI 2.1 to 8.4), and the odds of meeting criteria for mild cognitive impairment or dementia were higher in winter and spring (odds ratio 1.31, 95% CI 1.10 to 1.57) (Lim et al., 2018).
The two results are not in conflict; they are about different people measured in different ways. The controlled study isolated season in young adults by removing every other seasonal cue, which is exactly what makes it a poor guide to a real workplace where season arrives bundled with daylight, illness, holidays, and workload. The cohort study kept all of that noise and found a clinically meaningful pattern in an older population near a diagnostic threshold. Neither licenses a general claim about working-age staff completing ordinary work.
Why this matters for how the year is planned
The practical temptation is to schedule analytical work for one season and collaborative work for another. Nothing in this evidence supports that. One study found no seasonal performance difference in young adults and the other measured older adults, many with underlying pathology, on clinical cognitive batteries rather than on job tasks. No study here observed anyone doing their actual work.
What both do support is treating the calendar as a source of variation worth measuring rather than assuming. If a winter dip appears in your own error rates, absence, or throughput, it is measurable locally and worth acting on locally. Attributing it in advance to a published seasonal curve imports a number from a population that may share nothing with yours.
What this means for your schedule
- Do not reschedule complex work by season on the strength of the brain-imaging result; it reported neural activity, with performance explicitly stable.
- Treat the older-adult cohort finding as relevant to clinical and care settings, and to workforces where cognitive screening matters, rather than to office task performance generally.
- If you suspect a seasonal effect in your operation, measure your own outcomes across at least a full year before designing around it.
- Be suspicious of any source quoting a peak month for a cognitive skill without saying whether performance or brain activity was measured.
The business case
Seasonal work-allocation policies are cheap to announce and expensive to unwind, and the evidence usually cited for them does not show a seasonal performance difference in working-age adults.
The defensible version of this idea is a measurement programme: baseline your own throughput and error rates by month, then decide whether a seasonal pattern exists in your setting.
Frequently asked questions
- Does attention really peak in June and working memory in September?
- Brain activity did, in one study of 28 young adults (Meyer et al., 2016). The maximum response for the sustained-attention task fell near the summer solstice and the maximum for the working-memory task near the autumn equinox. Performance on those tasks did not vary significantly across the year, so the peaks describe neural cost rather than capability.
- Why were participants kept away from seasonal cues?
- To isolate season from everything that normally travels with it. Each participant spent about four and a half days without daylight or outside contact before testing, so differences could not be attributed to that weekโs sleep, light exposure, or social schedule. It is a strong design for the biological question and a weak one for predicting behaviour in an ordinary working week.
- Is there any evidence that cognition itself varies by season?
- Yes, in older adults. Across 3,353 participants in five cohorts, cognition was higher in summer and autumn than in winter and spring by an amount equivalent to 4.8 years of age difference, with higher odds of meeting criteria for mild cognitive impairment or dementia in the colder half of the year (Lim et al., 2018). This is observational and concerns an older population.
- Should we plan strategy work for autumn?
- Not on this evidence. No study here measured people performing their jobs, one found performance unchanged across seasons, and the other studied older adults on clinical cognitive tests. If autumn suits your planning cycle for commercial reasons, that is a fine reason. Neurobiology is not currently one.
- Could winter darkness still affect how people work?
- It plausibly affects sleep timing and sleepiness, which is a separate question with its own evidence. Seasonal daylight has been shown to delay sleep and raise sleepiness among high-latitude indoor workers. That is a fatigue and scheduling question rather than a claim about cognitive capacity varying with the calendar.
Sources
Every figure on this page is drawn from a cited primary source and checked against the original publication.
Meyer, C., Muto, V., Jaspar, M., Kussรฉ, C., Lambot, E., Chellappa, S. L., Degueldre, C., Balteau, E., Luxen, A., Middleton, B., Archer, S. N., Collette, F., Dijk, D.-J., Phillips, C., Maquet, P., & Vandewalle, G. (2016). Seasonality in human cognitive brain responses. Proceedings of the National Academy of Sciences, 113(11), 3066โ3071. https://doi.org/10.1073/pnas.1518129113
Design: Cross-sectional fMRI study of 28 young adults kept 4.5 days in an environment free of seasonal cues
Lim, A. S. P., Gaiteri, C., Yu, L., Sohail, S., Swardfager, W., Tasaki, S., Schneider, J. A., Paquet, C., Stuss, D. T., Masellis, M., Black, S. E., Hugon, J., Buchman, A. S., Barnes, L. L., Bennett, D. A., & De Jager, P. L. (2018). Seasonal plasticity of cognition and related biological measures in adults with and without Alzheimer disease: Analysis of multiple cohorts. PLOS Medicine, 15(9), e1002647. https://doi.org/10.1371/journal.pmed.1002647
Design: Analysis of five observational cohorts, 3,353 older adults, community and memory-clinic based
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Why this page is graded moderate evidence
A consistent systematic review or meta-analysis at a lower grade, or a large observational study whose authors disclaim causality.
Who reviewed this
Every article in this library is checked against its primary sources by the Soon operations research team: each figure is traced back to the study it came from, and the wording is checked against the study design before publication. What that review covers
None of the studies cited here evaluated Soon.They examine scheduling practices, shift patterns, and working hours as studied by independent researchers, so their findings describe what those practices are associated with, not what any particular software produces.
This article summarizes published research for scheduling and operations decisions. It is not medical advice. Individual health questions belong with a qualified clinician.
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