Indeed, selective silencing of the clock gene Per2 in the LHb in rats induced depression-like behavior at night, (Li et al., 2021) and deletion of Per1 in the LHb suppressed the beneficial effects of light on despair related behavior (Olejniczak et al., 2021) suggesting that Per genes may play an important role in the pathogenesis of depression. Here, PER2 is linked to depressive symptom measurement.