Time of day differences in neural reward responsiveness in children.

The Reward Positivity (∆RewP) event-related potential (ERP), generally quantified as the difference between neural responsiveness to monetary gains (RewP-Gain) and losses (RewP-Loss) is commonly used as an index of neural reward responsiveness. Despite the popularity of this ERP component in studies of reward processing, knowledge about the role of state-related influences on the ∆RewP is limited. The present study examined whether ∆RewP amplitudes may differ based on when during the day they are assessed and whether age or sex would moderate this link. Participants were 188 children between the ages of 7 and 11 (47.3% female) without a lifetime history of a major depressive disorder or any anxiety disorder recruited from the community. Children completed the Doors task during which continuous electroencephalography was recorded to isolate the ∆RewP. To better isolate this ERP component from other temporally or spatially overlapping ERPs, we used temporospatial principal component analysis. We found that time of day (ToD) differences in the ∆RewP amplitude varied based on children's age. Specifically, older, compared to younger, children exhibited stronger responses to gains versus losses between 11:15 a.m. and 12:30 p.m. and after around 5:15 p.m. Further, these age-related differences appeared to be driven specifically by older children's reduced neural responsiveness to losses. The findings have methodological implications by highlighting the importance of accounting for the ToD at which ∆RewP-focused study sessions are conducted as well as for demographic characteristics of the participants, such as their age.