BACKGROUND: Reward behavior in animals is influenced by circadian genes, including clock-pathway genes such as Period2 (PER2). Several forms of psychiatric illness are associated with both altered reward function and disturbances in circadian function. The PER2 single nucleotide polymorphism (SNP) rs2304672 has been associated with psychiatric illnesses involving reward dysfunction. Associations among circadian genes, function in neural reward circuits, and circadian-influenced behavior have not yet been studied in humans, however.
METHODS: 90 healthy adolescents underwent functional magnetic resonance imaging during a guessing task with monetary reward, genotyping for two PER2 SNPs (rs2304672, rs2304674), and actigraphy to measure sleep in their home environments. Weekend sleep midpoint, a behavioral index of circadian function, was derived from actigraphy. Puberty was measured by physical exam.
RESULTS: The rs2304672 SNP predicted blood oxygenation level-dependent response to monetary reward as constrained by sleep midpoint. Later sleep midpoint was associated with reduced activity in a key component of reward circuitry, medial prefrontal cortex (mPFC; Brodmann area 9/10/32), to reward outcome (p(corrected) < .05). G allele carriers showed reduced activity in mPFC relative to CC homozygotes.
CONCLUSIONS: Our findings are the first to indicate that circadian genes have a significant impact upon circadian-relevant reward circuitry in humans. These findings have the potential to elucidate gene-brain-behavior relationships underlying reward processing and psychopathology.
