Optogenetic stimulation of TH+-LC neurons facilitates memory retention. (A and B) Experimental design for optogenetic preencoding (A) and postencoding (B) stimulation. Optogenetic stimulation of LC-TH+ neurons was scheduled either 45 min before memory encoding (A) in the event arena or, in a separate session, 30 min after encoding (B). A PT was scheduled 24 h later. (C) The Th-Cre ChR+ group that received optogenetic stimulation with red light (Light-ON) displayed good memory at 24 h (F = 7.48, df = 1/8, P < 0.01), and the Th-Cre ChR+ control group that did not receive optogenetic stimulation (Light-OFF) and in the Th-Cre ChR– control animals were at chance level (1-sample t test, t = 6.26, df = 1/8, P < 0.001). Means ± SEM and individual animal data plots. Dashed line in panel C indicates chance level. ns, not significant. **P < 0.01.