Daily changes in smell discrimination depend on internal clock genes but not the brain’s main timekeeper

Olfactory sensitivity increased approximately 6-fold from a minimum during the day to a peak in the early night.

• Circadian changes in olfactory discrimination may depend on a genetic clock outside the suprachiasmatic nucleus (SCN).
• Olfactory sensitivity rhythms were observed even in mice with SCN lesions and those lacking the Npas2 gene.
• Loss of circadian olfactory sensitivity occurred in mice without Bmal1 or both Per1 and Per2 genes.
• Olfaction may represent a circadian behavior independent of locomotor activity and SCN function.

Simplified