So that's what the afternoon slump is all about!

The brain’s reward centre activates differently across the day, peaking in the morning and evening, say mental health experts whose research on healthy young men is published in the Journal of Neuroscience.

This finding contrasts with previous work that suggests behavioural measures of reward activation peak around the early afternoon.

The significance of this discovery, made by a team at Swinburne University, is that it shows the brain’s reward system is probably connected to the internal clock that primes 24-hour physiological