Nature's clocks and human mood: the circadian system modulates reward motivation.
Existing literature on reward motivation pays scant attention to the fact that reward potential of the environment varies dramatically with the light/dark cycle. Evolution, by contrast, treats this fact very seriously: In all species, the circadian system is adapted to optimize the daily rhythm of environmental engagement. We used 3 standard protocols to demonstrate that human reward motivation, as measured in the dynamics of positive affect (PA), is modulated endogenously by the circadian clock. Under naturalistic conditions, 13.0% of PA variance was explained by a 24-hr sinusoid. In a constant routine protocol, 25.0% of PA variance was explained by the unmasked circadian rhythm in core body temperature (CBT). A forced desynchrony study showed PA to align with CBT in exhibiting circadian periodicity independent of a 28-hr sleep/wake cycle. It is concluded that the circadian system modulates reward activation, and implications for models of normal and abnormal mood are discussed.
Murray
Greg
G
Psychological Science and Statistics, Swinburne University of Technology, Hawthorn, Victoria, Australia. gwm@swin.edu.au
Nicholas
Christian L
CL
Kleiman
Jan
J
Dwyer
Robyn
R
Carrington
Melinda J
MJ
Allen
Nicholas B
NB
Trinder
John
J
D000293:Adolescent; D000328:Adult; D000339:Affect; D001143:Arousal; D001831:Body Temperature; D002940:Circadian Rhythm; D034201:Computers, Handheld; D056348:Emotional Intelligence; D005260:Female; D005783:Gender Identity; D006801:Humans; D007206:Individuality; D008297:Male; D009042:Motivation; D009043:Motor Activity; D012016:Reference Values; D012201:Reward; D012931:Social Environment; D055815:Young Adult