Affective valence of neurons in the vicinity of the rat amygdala: Single unit activity in response to a conditioned behavior and vocal sound playback.

We recorded single unit activity within and around the rat amygdala while rats were engaged in an operant task (which included both reward and aversive trials) and during playback of ultrasonic vocalizations (USVs) to determine if there existed neurons which responded to two different types of either positive contexts (i.e., water reward and positively associated 50kHz vocalizations) or negative contexts (i.e., white noise and negatively associated 22kHz vocalizations). Ultimately, we wanted to determine if these two contexts (operant condition task and vocal sounds) could be represented as either positive or negative in a single neuron. Neural activity in 90% of cells was modulated in response to one or more of those events. A small number of those cells showed neural responses to both the aversive operant trials and 22kHz USVs, but did not show responses to reward operant trials or 50kHz USVs, suggesting the activity of these neurons encodes for similar negative emotion in response to these two contexts. Some cells showed responses to either the reward trials or 50kHz USVs, but no cells showed responses to both, suggesting that these cells do not show a common response to events associated with positive emotion. This might mean that 50kHz vocal sounds and the operant rewards were segregated into two different categories within the neural representation at the level of the amygdala, even though it appeared that both events were associated with positive emotions in rats.