Fig. 4.

Light enhances conditioned fear responses in Opn4^−/− mice. (A–C) In Opn4^−/− mice light does not significantly enhance freezing to a conditioned cue during conditioning (A) but does enhance freezing during 2 subsequent days of testing (B and C) (n = 14 in light, n = 6 in dark). (D) Freezing during ITIs was not significantly different between light and dark groups during conditioning and testing day 2, but a slight elevation was observed during testing day 1. In A–C evaluations are repeated-measures ANOVA, and in D evaluations are t tests, with P < 0.05 considered significant. *P < 0.05, **P < 0.01. Data are presented as average percentage freezing ± SEM.