Abstract
We have shown previously that CA1 conveys significant neural signals necessary to update value of the chosen target, namely chosen value and reward signals. To better understand hippocampal neural processes related to valuation, we compared chosen value- and reward-related neural activity between the CA3 and CA1 regions. Single units were recorded with tetrodes from the dorsal CA3 and CA1 regions of rats performing a dynamic foraging task, and chosen value- and reward-related neural activity was estimated using a reinforcement learning model and multiple regression analyses. Neural signals for chosen value and reward converged in both CA3 and CA1 when a trial outcome was revealed. However, these neural signals were stronger in CA1 than CA3. Consequently, neural signals for reward prediction error and updated chosen value were stronger in CA1 than CA3. Together with our previous finding that CA1 conveys stronger value signals than the subiculum, our results raise the possibility that CA1 might play a particularly important role among hippocampal subregions in evaluating experienced events.
Highlights
As a structure known for its essential role in encoding episodic memory, the hippocampus has not been a popular target for investigation of the neural underpinning of value-based decision-making
All rats showed biased choices toward the higher-rewardprobability target after block transition, an effect that was well-captured by a reinforcement learning (RL) model (Huh et al, 2009) (Figure 1B)
We replicated our previous findings in the present study; reward and chosen value signals converge in CA1 when trial outcome was revealed
Summary
As a structure known for its essential role in encoding episodic memory, the hippocampus has not been a popular target for investigation of the neural underpinning of value-based decision-making. When we remember a past episode, we usually remember what happened, and its affective component—how good or bad—as well In this regard, significant value signals have been found in the human (Tanaka et al, 2004; Bornstein and Daw, 2013) and rat (Lee et al, 2012) hippocampus, raising the possibility that factual and value information may be conjunctively encoded in the hippocampus such that the memory of an event is inseparable from the memory of its value. Concurrent coding of factual and value information would be useful for simulating hypothetical outcomes and assessing their values It is well-established that the hippocampus is important for memory, but CA1 and CA3 Value Signals for imagining new experiences (Buckner, 2010; Schacter et al, 2012; Gaesser et al, 2013; Mullally and Maguire, 2014). Value information represented in the hippocampus would be useful for simulating most probable and rewarding scenarios for maximizing value
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