PER1 and Anxiety: Intriguingly, Per1 in the lateral habenula was necessary for the antidepressant effect of light but loss of Per1 in the lateral habenula did not affect anxiety-like behavior in the O-maze, indicating that increased anxiety-like behavior observed in Per1 global knockout mice is attributed to loss of Per1 somewhere else in the brain, potentially the SCN (Olejniczak et al., 2021).