dCA1 cells encode and update contextual place preference

Pyramidal cells in the dorsal hippocampus (dCA1) are excitatory neurons modulated by environmental cues. While a population of dCA1 cells encodes spatial location, other groups are activated by reward probability and encounters. Since "rewards" are predicted at "locations," we sought to determine how spatiotemporal coding patterns in the dCA1 resolve contextual preference and subsequent change in preference that is driven by reward encounters. Specifically, we examined these encoding patterns in biased place-preference tasks for simple reward acquisition and for complex discrimination of reward magnitudes. Initial behavioral tests for mice without neural implants revealed a higher sensitivity to discriminating between two locations associated with reward magnitude, in comparison to reward detection. Analysis of dCA1 single-unit spatiotemporal activity during pre-conditioning revealed that these cells exhibited peak firing as they approached the less preferred context. Therefore, when the contextual preference is biased toward a reward or a higher-magnitude reward, a change in dCA1 firing rate around context entry events reflects the updated spatial preference. Interestingly, the context of lower preference with no associated reward or a lower-value reward elicits a stronger firing response than the alternative contexts with higher reward values. Together, we conclude that the spatiotemporal firing patterns of dCA1 single units and the threshold of peak FR change encode contextual preference. Ultimately, the spatiotemporal pattern is updated (remapped) when there is a change in the contextual preference driven by reward contingencies.