Our data from fear conditioning were highly suggestive of an mPFC-to-BLA safety signal in the gamma range. To confirm that the same physiological correlates could be observed in other safe contexts, we first evaluated changes throughout extinction of conditioned fear, as animals learned that the previously aversive CS+ no longer posed a threat. After an additional two days of exposure to CSs without shock, animals returned to a baseline level of freezing (~20%; Figure 8A; n=11). Throughout extinction, there was a steady increase in BLA and mPFC fast gamma power during tone presentations (Figure 8B, C; p<.05, MLR). Notably, this effect was seen both for animals that began as discriminators and those that began as generalizers (data not shown), suggesting that these changes reflect safety signals, rather than the active process of discrimination, which could not be disentangled during fear recall. At the same time, we saw an enhancement of the GCImPFC→BLA (Figure 8D; p=4.7 × 10−5, MLR), without a corresponding change in the GCIBLA→mPFC (p=.97), suggesting that the observed increase in fast gamma power was the result of enhanced
