The Effects of Daytime Melatonin Administration on Sleep, Higher Cognitive Function, and Changes in the Brain

This study investigated the effects of exogenous melatonin on people’s sleep, ability to perform an emotional Stroop task, and underlying brain architecture. 10 healthy adults (age = 26.8 ± 6.25 years) underwent a baseline period followed by an experimental period whereby melatonin was administered at inappropriate times, with daily activity logs kept throughout. The emotional Stroop task was performed four times during each period, followed by an MRI scan. Following melatonin administration, sleep and wake times were significantly shifted and sleep quality ratings were significantly decreased compared to baseline values. Additionally, processing of emotional words but not faces was negatively affected by the melatonin treatment. Fractional anisotropy and mean diffusivity values were also significantly altered in the inferior frontal gyrus. It is inferred that the melatonin treatment induced circadian desynchronization, resulting in behavioural changes and structural alterations in brain regions involved in performance of the emotional Stroop task.