Heterogeneous single-cell dynamics support stable population codes for objects in the mouse anterior cingulate cortex

Remembering our environment and its principal features is essential to our survival. The anterior cingulate cortex (ACC) has been implicated as a key region in remote memory (Frankland et al., 2004; Goshen et al., 2011; Almaguer-Melian et al., 2025). Whilst most studies investigating the ACCs contribution to memory have used fear conditioning, some have highlighted a role in the retention of object locations across various timescales, both recent and remote (Weible et al., 2009, 2012). However, how neurons in the ACC encode object locations across repeated exposure has not been investigated. Here, we investigated if object representations are supported by cell assemblies that are stable over days, or if the representation is volatile and dynamic across repeated experiences separated across time. Using calcium-imaging in freely moving mice, we recorded the activity of excitatory ACC neurons while mice explored objects placed in an environment over repeated days. We find that the ACC encodes object location in a mostly dynamic fashion: while the proportion of neurons allocated to object coding does not change across days, the specific neurons exhibiting object correlates fluctuate, featuring a dynamic turnover with a smaller set of stable cells. Interestingly, this was modulated by the animals behaviour, such as object cells from mice spending the most time exploring the objects showed a higher degree of stability. We next examined how dynamic single-cell coding relates to stability at the network level. Population analyses revealed stable representations emerging from collective dynamics, suggesting that downstream regions may rely on ensemble patterns rather than fixed cell identities. Decoding analyses supported this view: ensembles of 64-128 neurons were as accurate and more efficient than the full dataset, indicating that information about the animals location becomes more linearly separable when represented at a coarser population scale, making it more readily accessible to downstream regions that integrate population-level activity. Thus, we show that the ACC achieves stability through emergent organization across neurons, even as individual cells remain dynamic.