Winter Brain, Summer Brain: Seasonality in Brain Responses?

A new paper in PNAS raises the interesting suggestion that our brain function goes through yearly cycles. According to authors Christelle Meyer and colleagues, their findings reveal new evidence of seasonal effects in human cognitive brain function "that could contribute to cognitive changes at specific times of year." However in my view, the study is too small to be conclusive. Meyer et al. used fMRI to scan 28 young participants. Each of the volunteers spent 4 1/2 days in a laboratory "devoid of seasonal cues", which included a period of sleep deprivation, before being scanned.