a, b, Top left: ex vivo whole-cell patch clamp and cell-attached recordings of ChR2–mCherry-expressing PV + ( a) and SOM + ( b) BLA interneurons in amygdala slices. Top right: distinct firing patterns of PV + ( a) and SOM + ( b) cells in response to depolarizing somatic current injection. Bottom: PV + ( a) and SOM + ( b) cells fire brief bursts of action potentials in response to short blue light stimulation (468 nm, 5 ms, 10 mW) and show sustained firing during prolonged stimulation (468 nm, 300 ms, 10 mW, cell-attached recordings). c, Single-unit recordings of optogenetically identified PV + (green) and SOM + (red) interneurons upon 300-ms stimulation with blue (ChR2, top) or yellow (ARCH, bottom) light in behaving animals. Left: Z-scored activity. Right: firing frequency. d, Left: comparison of spontaneous and light-evoked superimposed average spike waveforms of all PV + interneurons identified by optogenetic activation. Middle: linear correlations between spontaneous and light-evoked spikes were calculated for individual optogenetically identified PV + interneurons. Only cells with r values above 0.95 were considered as directly light-activated. Right: jitter of first light-evoked spikes in identified PV + cells. e, Change point analysis for determination of the latency of light-evoked activity changes. The cumulative sum of the activity of a neuron was calculated and the change point was determined. Shown is an example of ARCH-mediated inhibition for the entire illumination period (left) and at the light onset (right). The arrow indicates the change point. f, Expression of ChR2, co-expressed with Venus (green), is restricted to SOM + interneurons (red). g, Specificity of opsin-expression. Left: examples of opsin expression in a PV–Cre (top) and a SOM–Cre (bottom) animal with immunohistochemistry (IHC) for the respective other interneuron marker. Right: quantification of co-localization of opsin-expressing and IHC-labelled cells. h, Light-induced changes in activity of SOM + interneurons upon illumination with either blue or yellow light for activation of ChR2 or ARCH, respectively. i, Latencies and Z scores of light-induced activity changes in optogenetically identified SOM + interneurons. j, Left: comparison of average waveforms of spontaneous and light-evoked spikes in SOM + interneurons. Middle: linear correlations between spontaneous and light-evoked spikes in optogenetically identified SOM + interneurons. Right: jitter of first light-evoked spikes in identified SOM + cells.