Given that discriminators demonstrated enhanced fast gamma power during the CS− compared to the CS+, we anticipated that they would show stronger local gamma-frequency synchrony during the CS−than the CS+. Indeed, we found that in discriminators, a higher percentage of multi-unit recordings were significantly phase-locked to fast gamma oscillations during the CS− than CS+ (Figure 4C; p<.05, McNemar's test). Phase-locking to theta or slow gamma was not affected by stimulus type (Figure S4F; p > .05), suggesting that this safety-related change is highly specific. We also evaluated the relationship between phase-locking differences and discrimination on a continuous scale (rather than relying on a significance threshold), quantifying phase locking strength, as measured by MRL, for every multi-unit recording. Multi-unit firing of discriminators was more strongly phase locked to fast gamma during the CS−than the CS+ (Figure 4D; p<.01, sign-rank). Importantly, for generalizers, the strength of phase-locking to fast gamma did not differ by CS (Figure 4C; p>.05, McNemar's test; Figure 4D; p>.05, sign-rank). Taken together, these data demonstrate that neural activity in the BLA is synchronized during fast gamma oscillations, and this synchronization is enhanced during stimuli the animal treated as signaling safety.
