Role of the hippocampal CA1 region in incremental value learning

Abstract

It is generally believed that the hippocampus plays a crucial role in declarative memory—remembering facts and events—but not in gradual stimulus-response association or incremental value learning. Based on the finding that CA1 conveys strong value signals during dynamic foraging, we investigated the possibility that the hippocampus contributes to incremental value learning. Specifically, we examined effects of inactivating different subregions of the dorsal hippocampus on behavioral performance of mice performing a dynamic foraging task in a modified T-maze. A reinforcement learning model-based analysis indicated that inactivation of CA1, but not dentate gyrus, CA3, or CA2, impaired trial-by-trial updating of chosen value without affecting value-dependent action selection. As a result, it took longer for CA1-inactivated mice to bias their choices toward the higher-reward-probability target after changes in reward probability. Our results indicate, contrary to the traditional view, that the hippocampus, especially CA1, might contribute to incremental value learning under certain circumstances.

Distinct roles of striatal direct and indirect pathways in value-based decision making

“…Hence, the task required the animal to discover reward probabilities and the optimal choice based on the history of past choices and their outcomes. As shown previously in a similar TAB task (Jeong et al, 2018), the probability of choosing the lower-reward–probability target did not increase as a block transition approached, arguing against the possibility that animals were able to estimate the time of reversal (Figure 3—figure supplement 1). Consistent with this finding, animal choice behavior in this task was well captured by the Q-learning model, a simple reinforcement learning model (Sutton and Barto, 1998) (Figure 3a).…”

“…Even though we did not test eGFP-CNO mice in the dynamic foraging task, selective effects of CNO on D1R-Cre versus D2R-Cre mice (as opposed to common CNO effects on both mouse lines) argue against non-specific effects of CNO. We also failed to find nonspecific effects of CNO on learning rate or randomness in action selection in our previous study (Jeong et al, 2018). There remains a possibility that inactivation of D1R- and/or D2R-expressing striatal interneurons (GABAergic fast-spiking interneurons and cholinergic tonically active neurons) might have contributed to the observed behavioral effects.…”

Remembering rewarding futures: A simulation‐selection model of the hippocampus

“…These functions are related to spatial/cognitive processes, but not valuation. As mentioned earlier, recent studies suggest that CA1 may be uniquely involved in valuation among different hippocampal subregions (Jeong et al, ; Lee et al, ; Lee et al, ). Our model assumes that CA1 value processing is related to its core function (selecting high‐value sequences), whereas most existing models, to the best of our knowledge, do not consider valuation itself as one of the major underlying variables that affect CA1 functions.…”

“…This is consistent with the finding in rats that CA1 neurons, but not CA3 neurons, remap their place fields when rewarding locations are reconfigured (Dupret, O'Neill, Pleydell‐Bouverie, & Csicsvari, ). Moreover, chemogenetic inactivation of CA1, but not CA3, CA2 or DG, of the dorsal hippocampus impairs value learning without affecting value‐dependent action selection in mice performing a dynamic foraging task in a modified T‐maze (Jeong et al, ). Although additional studies will be required to reveal the details of value information processing in the hippocampus, these results make a strong case for CA1’s role in valuation.…”

Enhanced Contextual Fear Memory and Elevated Astroglial Glutamate Synthase Activity in Hippocampal CA1 BChE shRNA Knockdown Mice

“…The hippocampus is involved in contextual fear memory formation and has been highlighted to play a key role in the etiology of PTSD (11,12). This brain region is involved in the rapid acquisition of CFC and the retrieval of contextual memory after a long time (i.e., 24 h) as well as the consolidation process, which is important for long-term contextual fear memory (12,16,17).…”