CLOCK-dependent pathway in a single pair of LNd neurons instruct circadian-independent interval timing behavior.

Interval timing is a cognitive ability essential for behaviors such as mating, foraging, and decision-making, and it is distinct from circadian rhythm regulation. Despite the involvement of circadian clock genes in both interval timing and circadian rhythms, the mechanisms differentiating these functions remain unclear. Using Drosophila as a model, we demonstrate that the CLK/CYC heterodimer, but not PER/TIM, is essential for interval timing. Neuronal CLK/CYC expression is necessary and sufficient for sexual experience-dependent shorter mating duration (SMD) behavior. We identified that CLK/CYC expression in a single pair of ITP-positive LN _d neurons is pivotal for SMD. These neurons are glutamatergic with output circuits to central brain regions. CLK variants lacking DNA binding motifs dissociate circadian rhythms from interval timing and sleep behaviors in these neurons. Our study uncovers a specialized circuit for interval timing and highlights the non-circadian functions of circadian clock genes.