Eveningness and distinctness of the circadian rhythm in men are related to altered neural responses to gain and loss.

Circadian rhythmicity is considered to be one of the factors modulating the functions of the brain's motivational system. To date, research has primarily focused on the unidimensional morningness-eveningness continuum (phase of the circadian rhythm), while the second dimension - distinctness (subjective amplitude) has been neglected. In this study, we explored the relationships of distinctness and eveningness with neural correlates of motivated behavior. In 37 healthy men (aged 20-30), we measured the characteristics of circadian rhythmicity using the Morningness-Eveningness-Stability-Scale improved (MESSi) questionnaire and employed additional psychometric assessments. To determine the gain- and loss-motivated behavior, we used fMRI during the Monetary Incentive Delay task. We found that higher distinctness was positively related to the: activation in the ventral tegmental area during the anticipation of punishment; activation in the left occipital pole during the negative feedback; elevated neuroticism and behavioral inhibition system scores. Eveningness was associated with increased activation in the left frontal pole, middle temporal gyrus, inferior temporal gyrus, and temporal fusiform cortex during the positive feedback. These results improve our understanding of the relationship between distinctness, eveningness, and motivated behavior. They constitute a promising direction for further studies on the multidimensionality of circadian rhythms.