The part of your brain responsible for motivation, reward-processing, and generally being a good friend and employee basically checks out somewhere around 2 p.m., according to a new study in the Journal of Neuroscience. While past research has shown that our energy dips after lunch, this study is the first to use functional magnetic resonance imaging (fMRI) to find a neurological reason why—so you can blame your brain, instead of your meatball sub.
“This is a novel finding and has significant implications for neuroscience research, which normally ignores time of day as a variable,” study coauthor Greg Murray of Swinburne University of Technology in Australia told Fatherly.
Studies dating back as early as 1986 show evidence that the post-lunch dip that we’ve all experienced has little to do with what we’re actually eating and more to do how both human and animal reward systems are linked to circadian clocks. Most of these studies, however, were self-reported. None bothered looking at the neuroscience.
So Murray and colleagues compared the activation of the brain’s reward system in a small sample of 16 healthy men at 10 a.m., 2 p.m., and 7 p.m, while they were performing a battery of “gambling” exercises that involved motor skills and learning. Results of the fMRI scans, which measure blood flow to specific regions in the brain (albeit not always reliably) suggested that activity in the left putamen, part of the reward region of the brain, was lowest at 2 p.m. Not because the putamen turns off when the clock strikes two, the researcher say, but because the putamen appears to be “primed to expect rewards at this time, and so didn’t react as strongly as at other times of day,” Murray explains. In other words, our brains are somewhat nonplussed about rewards around 2pm—because they kind of expect it.
The most obvious caveat of the study is the small sample size, but Murray says an even larger issue is that the results raise more questions than they answer. Specifically, if this part of the reward region is relatively deactivated at 2 p.m., then why don’t we all spiral into a slump at 2 p.m. every day—and why do some frustratingly happy people actually report that their moods improve after lunch? He suspects the striatum may be involved, but further study is necessary.
In terms of what people can do about the 2 p.m. slump, Murray recommends getting outdoors during lunchtime and moving around as much as possible throughout the day to mitigate these effects. (Sorry, coworkers). And for parents, the findings reinforce the importance of enforcing a routine for children’s overall emotional and physical wellbeing.
“Our research shows that this rhythmicity is fundamental to how the brain organizes human motivation across the day,” Murray says. “Earth’s entire environment is rhythmic, and we would be wise to get in sync.”