Summary: A new Journal of Neuroscience study reveals the activation of a brain area associated with reward response early in the afternoon.
Source: SfN.
Understanding how activity in the brain’s reward system changes throughout the day could have implications for depression, substance abuse and sleep disturbances.
Activation of a reward-processing brain region peaks in the morning and evening and dips at 2 p.m., finds a study of healthy young men published in The Journal of Neuroscience. This finding may parallel the drop in alertness people tend to feel in mid-afternoon.
Greg Murray and colleagues compared activation of the brain’s reward system in 16 men during a gambling task at 10 a.m., 2 p.m. and 7 p.m. They found that activation in the left putamen was lowest in the early afternoon. The result contrasts with previous research showing that people report being in the best mood — a subjective measure of reward activation — at this time. The authors suggest that activation is greater in the morning and evening because rewards are not expected at these times.
Understanding the timing of reward response could have implications for the treatment of disorders in which symptoms fluctuate throughout the day, such as depression, substance abuse and sleep disturbances. This work also calls into question neuroimaging studies that do not control for or report the time of day when scanning took place.
Funding: The study was supported by Barbara Dicker Brain Sciences Foundation.
Source: Lauren Quinn – SfN
Image Source: NeuroscienceNews.com image is credited to Byrne et al., The Journal of Neuroscience.
Original Research: Abstract for “Time of day differences in neural reward functioning in healthy young men” by Jamie E. M. Byrne, Matthew E. Hughes, Susan L. Rossell, Sheri L. Johnson and Greg Murray in Journal of Neuroscience. Published online August 21 2017 doi:10.1523/JNEUROSCI.0918-17.2017
[cbtabs][cbtab title=”MLA”]SfN “Afternoon Slump in Reward Response.” NeuroscienceNews. NeuroscienceNews, 21 August 2017.
<https://neurosciencenews.com/brain-changes-reward-7342/>.[/cbtab][cbtab title=”APA”]SfN (2017, August 21). Afternoon Slump in Reward Response. NeuroscienceNew. Retrieved August 21, 2017 from https://neurosciencenews.com/brain-changes-reward-7342/[/cbtab][cbtab title=”Chicago”]SfN “Afternoon Slump in Reward Response.” https://neurosciencenews.com/brain-changes-reward-7342/ (accessed August 21, 2017).[/cbtab][/cbtabs]
Abstract
Time of day differences in neural reward functioning in healthy young men
Reward function appears to be modulated by the circadian system, but little is known about the neural basis of this interaction. Previous research suggests that the neural reward response may be different in the afternoon; however the direction of this effect is contentious. Reward response may follow the diurnal rhythm in self-reported positive affect, peaking in the early afternoon. An alternative is that daily reward response represents a type of prediction error, with neural reward activation relatively high at times of day when rewards are unexpected (i.e., early and late in the day). The present study measured neural reward activation in the context of a validated reward task at 10.00h, 14.00h, and 19.00h in healthy human males. A region of interest blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) protocol was used to investigate the diurnal waveform of activation in reward-related brain regions. Multi-level modelling found, as expected, a highly significant quadratic time-of-day effect focusing on the left putamen (p <.001). Consistent with the ‘prediction error’ hypothesis, activation was significantly higher at 10.00h and 19.00h compared to 14.00h. It is provisionally concluded that the putamen may be particularly important in endogenous priming of reward motivation at different times of day, with the pattern of activation consistent with circadian-modulated reward expectancies in neural pathways; viz., greater activation to reward stimuli at unexpected times of day. This study encourages further research into circadian modulation of reward, and underscores the methodological importance of accounting for time of day in fMRI protocols.
SIGNIFICANCE STATEMENT
This is one of the first studies to employ a repeated measures imaging procedure to explore the diurnal rhythm of reward activation. While self-reported reward (most often operationalised as positive affect) peaks in the afternoon, the present findings indicate that neural activation is lowest at this time. We conclude that the diurnal neural activation pattern may reflect a prediction error of the brain, where rewards at unexpected times (10.00h and 19.00h) elicit higher activation in reward brain regions than at expected (14.00h) times. These data also has methodological significance, suggesting that there may be a time of day influence which should be accounted for in neural reward procedures.
“Time of day differences in neural reward functioning in healthy young men” by Jamie E. M. Byrne, Matthew E. Hughes, Susan L. Rossell, Sheri L. Johnson and Greg Murray in Journal of Neuroscience. Published online August 21 2017 doi:10.1523/JNEUROSCI.0918-17.2017
