Active lever presses (ALP), inactive lever presses (ILP) and laser stimulations (LS) per minute during operant conditioning (n = 9 mice; LP: two-way repeated measures ANOVA, LP effect F (1,8) = 203, *** P < 0.001; session effect F (16,128) = 12.12, *** P < 0.001; LP time interaction F (16,128) = 11.23, *** P < 0.001). Data are mean s.e.m.