Dynamic encoding of valence by the anterior cingulate cortex in mice

Fear supports survival by linking environmental cues with potential threats, but its dysregulation contributes to anxiety disorders and PTSD. While the contributions of hippocampus and amygdala to fear memory are well established, the role of the anterior cingulate cortex (ACC) during and after acquisition remains less clear. Here we longitudinally recorded ACC neuronal activity using single-photon calcium imaging in freely behaving mice undergoing auditory fear conditioning. During cue pre-exposure, neural responses to the cue were strongest to early novel presentations and declined with repetition. During acquisition, responses emerged late in training as the cue became shock-predictive. Ensemble analysis identified subpopulations of "freezing on" and "freezing off" cells in the ACC whose activation coincided with decreased neural activity and increased neural synchrony. During 24-h and 48-h recall, ACC responses were robust to early presentations but diminished during late tones; similarly, a subpopulation of neurons emerged that was upmodulated by the CS in early 24-h and 48-h recall. Together, our results demonstrate that ACC neuronal response to a cue reorganizes both within and across sessions, with dynamic changes in population activity, recruitment, and synchrony that mirror changes in novelty and negative valence. This pattern suggests a role for ACC as a flexible hub that dynamically represents changes in cue significance.