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.
Psychological Science and Statistics, Swinburne University of Technology, Hawthorn, Victoria, Australia. gwm@swin.edu.au
Greg
G
Murray
Christian L
CL
Nicholas
Jan
J
Kleiman
Robyn
R
Dwyer
Melinda J
MJ
Carrington
Nicholas B
NB
Allen
John
J
Trinder
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