Diverse activity patterns of medium spiny neurons in the nucleus accumbens in reward and aversion

Abstract

Humans and animals adapt their behavior to acquire or avoid reward and aversive stimuli, respectively. However, the precise neural mechanisms that underly the signaling of such stimuli, as well as learnt associations between environmental cues and the rewarding/aversive stimuli they predict, are still unclear. Within the nucleus accumbens (NAc), a key neural substrate for limbic processing, dopamine D1 and D2 receptor-expressing medium spiny neuron (D1-/D2-MSNs) populations have been revealed to play important roles in controlling reward and aversion learning, respectively. Interestingly, recent reports have also suggested that within these populations there may be more complex neural circuit mechanisms contributing to the processing of limbic information. In this study, we expressed a calcium indicator in either NAc D1- or D2-MSNs and recorded neural activity at the single-cell level by miniature microscopy during reward and aversive Pavlovian learning. Diverse activity patterns were found in response to direct rewards (sucrose) and punishments (air puff), as well as environmental cues (auditory tones) paired with their delivery. These results suggest novel complexity in the control of reward and aversive learning by diverse activity patterns in subpopulations of NAc D1- and D2-MSNs.