Using the motor response of the animal as a measure of fear confounds the internal state (sense of fear or safety) of the animal with its motor response to that state. To disambiguate whether changes in fast gamma power and coupling to theta were associated with either safety or motor response, we performed two additional analyses. First, fast gamma power and theta-gamma coupling were calculated as a function of velocity in the same animals prior to fear conditioning, and second, these measures were calculated during periods of immobility (speed < 5 cm/s), allowing for the comparison of responses to the CS+ and CS− when motor behavior was equivalent. No association was found between fast gamma power and speed (Figure S4G), while for theta-fast gamma coupling, there was an inverted-U relationship with a peak at 6 cm/s, which could not explain our results. Moreover, the effects of stimulus type were present even during immobility epochs alone (Figure S4H-I). Thus, gamma coupling and power appear to be related to behavioral state rather than motor activity.
