ENSEMBLES IN THE VENTRAL HIPPOCAMPUS EXERT LONG-TERM CONTROL OVER HABIT-BASED BEHAVIOR

Habits are routinized behavioral patterns that can be elicited by environmental cues and occur almost automatically. The ventral hippocampus (vHC) is involved in the formation and execution of habits, and it can form stable ensembles controlling behavior. Here, we sought to investigate whether the vHC modulates habitual behavior via neuronal ensembles that remain functional throughout time. Using young mice, which are innately prone to display habit-like behavior, we tagged neurons that were active in the vHC during the execution of habit-like behavior. Later chemogenetic stimulation of these neuronal ensembles induced habit-like behavior under conditions in which mice typically demonstrate more goal-directed, flexible actions. Interestingly, though, chemogenetic inhibition of these ensembles did not block later habit-like behavior. Thus, neural ensembles in the vHC remain functional for long periods of time and are sufficient, but not necessary, to induce habitual response tendencies. We sought to further characterize these vHC ensembles by quantifying the overlap between neurons active during the formation vs execution of habitual actions. We found minimal overlap between cells active during habit formation vs execution, suggesting that the vHC recruits ensembles for habits that might change and drift over time. Future research will focus on understanding the specificity of these ensembles and what information they encode to promote habitual behavior.