(A) Diagram of oddball stimuli illustrating post-photostimulation tone number: tones and light pulses indicated as in Figure 3A. Numbers indicate each tone position relative to light pulses as included in the analysis below. Any tones following deviant tones were excluded from the analysis. (B) The mean population FR in response to standard (gray) and deviant (red) tones subsequent to light-on trials is not affected by light presentation (dark bars: light-off. light bars: light-on). For each neuron, responses are normalized by the response to the third post-laser standard tone (T3, indicated by blue dashed line). In PV-Cre mice, the standard tone-evoked FR with light-on (T0) and the tone preceding it (T−1) were significantly higher than that of standard T3 (N = 159, T−1: Δ = 10%, p2 = 0.037, t(158) = 2.9, C = 9. T0: Δ = 170%, p2 = 2e−7, t(158) = 5.9, C = 9), while the two post-light tones (T1 and T2) were not significantly different (N = 159, T1 and T2: p2 > 0.05, t(158) < 2.6, C = 9). In SOM-Cre mice, the light-on standard T0-evoked FR was greater than that of T3 (N = 114, Δ = 54%, p2 = 4e−8, t(113) = 6.4, C = 9), while all light-off tones were not significantly different (T−1, T1, and T2: p2 > 0.05, t(113) < 0.9, C = 9). In control mice, no standard tones evoked greater FR than T3, (N = 107, T−1 through T2: p2 < 0.05, t(106) < 2.7). In all three groups, deviant tones in all positions evoked greater FRs than standard T3, (Δ > 209%, p2 < 5e−5, t(106) > 4.7, C = 9). (C) Mean SSA index for each sequential tone position (for T−1, 0, 1, 2, 3) calculated based on the pair of standard and deviant tones at each respective position. Each tone response, tone A or B, was used to calculate a separate SSA index: Where S and D indicate mean FR evoked by standard and deviant tone probabilities, respectively, and their subscripts indicate the tone frequency condition. Compared to T3, SSA index was significantly reduced only for T0, the only light-on trial, in both PV-Cre and SOM-Cre mice (PV-Cre: Δ = −40%, p2 = 4e−10, t(158) = −6.9, C = 4. SOM-Cre: Δ = −29%, p2 = 2e−7, t(158) = −5.8, C = 4), as expected from Figure 3E–G. In both PV-Cre and SOM-Cre mice, the SSA index at all of the other sequential tone positions, T−1 through T2 was not significantly different than that of T3 (p2 > 0.05, t(113) < 1.9, C = 4), indicating that the effects of photosuppression were not detectable beyond T0. In control mice, the SSA index was not different compared to T3 for any tone position, even T0 (p2 > 0.05, t(106) < 1.8, C = 4). Together, this analysis demonstrates that the optogenetic effects are acute to illumination periods and unlikely to confound interpretation of effects observed during light-off trials. In all panels, single, and triple stars indicate p < 0.05 and 0.001, respectively.