We first analyzed recordings of BLA multi-unit activity, which are less subject to volume conduction than the LFP, although such recordings can be dominated by spikes from fast-spiking interneurons. One third of BLA multi-unit recordings (21/63) had statistically significant phase-locking (p<.05, Rayleigh's test) to BLA fast gamma oscillations during the CS+ (Figure 4A-B; p<.001 relative to shift predictor, McNemar's test). Spike-spike cross correlations (Supplementary Experimental Procedures) also revealed significant synchrony between simultaneously recorded multi-units during fast gamma oscillations (Figure S5; p<.001, sign-rank, n=102 pairs). These findings suggest that gamma oscillations are associated with synchronous neuronal activation in at least a subset of BLA neurons.
