シンポジウム
37 記憶回路における報酬信号
37 Reward representations in the entorhinal-hippocampal memory circuit
座長：五十嵐 啓（University of California, Irvine）・Boccara Charlotte N（University of Oslo） |
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| 2022年6月30日 16:10～16:40 ラグナガーデンホテル 羽衣：中 第9会場
1S09e-01
Reward related dynamics in the parahippocampal circuit
*Lisa Giocomo(1)
1. Stanford University School of Medicine
Keyword: Navigation, Reward learning, Memory
To learn and remember where to find reward in an environment, the brain's spatial map must be updated by reward predictive information. This spatial memory process relies, in part, on circuits in the parahippocampus. As reward locations are learned, spatial representations in the hippocampus and entorhinal cortex 'remap' their firing properties to represent reward locations. In ongoing work, we are investigating how the entorhinal cortex and hippocampus encode information regarding remembered reward locations and whether this remapping corresponds to the accuracy of behavior. | | 2022年6月30日 16:40～17:10 ラグナガーデンホテル 羽衣：中 第9会場
1S09e-02
Complementary roles of the hippocampus and the entorhinal cortices for reward learning and consolidation during sleep
*Charlotte Boccara(1), Michele Nardin(2), Federico Stella(3), Jozsef Csicsvari(2)
1. University of Oslo, 2. IST Austria, 3. Radboud University
Keyword: reward, hippocampus, medial entorhinal cortex, grid cells
Memory can be described as a two-step process. Step one is the learning – or encoding of new information in a temporary storage – the hippocampus – one of the first brain region affected by Alzheimer disease. Step two is the consolidation of newly learnt information and their transfer into a long-term storage in the cortex, where it will be accessible for later recall if a need arises. To understand how neural representation are encoded in the hippocampal region, we focused on goal encoding. We recently demonstrated that learning of reward locations can distort both hippocampal and entorhinal spatial maps. To that aim, we had trained rats to daily learn three new reward locations on a cheeseboard maze while recording from the medial entorhinal cortex and the hippocampal CA1 region. Many grid fields moved toward goal location, leading to long-lasting deformations of the entorhinal map. Therefore, distortions in the grid structure contribute to goal representation during both learning and recall, which demonstrates that grid cells participate in mnemonic coding and do not merely provide a simple metric of space. Here we present unpublished new analyses on how this process dynamically takes place during learning and subsequent consolidation during sleep. We specifically highlight (i) how hippocampal and entorhinal remap at different paces and (ii) that a hippocampo-entorhinal dialogue may be key to ensure reward encoding. Our results demonstrate how transfer of information occurring during sleep may shape neural (reward) codes. | | 2022年6月30日 17:10～17:40 ラグナガーデンホテル 羽衣：中 第9会場
1S09e-03
Dopamine facilitates encoding of cue-reward associative memory in the lateral entorhinal cortex
*Kei M Igarashi(1)
1. University of California, Irvine
Keyword: Reward, entorhinal cortex, associative memory, dopamine
Mounting evidence shows that dopamine in the striatum is critically involved in reward-based reinforcement learning. However, it remains unclear how dopamine reward signals influence the entorhinal-hippocampal circuit, another brain network critical for learning and memory. Using cell-type-specific electrophysiological recording, we found that dopamine signals from the ventral tegmental area/substantia nigra control encoding of cue-reward association rules in layer 2a fan cells of the lateral entorhinal cortex (LEC). When mice learned novel olfactory cue-reward associations using a pre-learned association rule, spike representations of LEC fan cells grouped newly learned rewarded cues with a pre-learned rewarded cue, but separated them from a pre-learned unrewarded cue. Optogenetic inhibition of fan cells impaired the learning of new associations while sparing the retrieval of pre-learned memory. Using fiber photometry, we found that dopamine sends novelty-induced reward expectation signals to the LEC. Inhibition of LEC dopamine signals disrupted associative encoding of fan cells and impaired learning performance. Our results suggest that LEC fan cells represent a cognitive map of abstract task rules, and that LEC dopamine facilitates the incorporation of new memories into this map. | | 2022年6月30日 17:40～18:10 ラグナガーデンホテル 羽衣：中 第9会場
1S09e-04
Encoding and consolidation of reward-related information in the hippocampus
*Attila Losonczy(1)
1. Columbia University
Keyword: hippocampus, sharp-wave ripple , imaging, navigation
The hippocampal-entorhinal circuitry in the mammalian brain supports goal-directed spatial navigation and learning. However, the precise nature and cellular/circuit-level mechanisms of reward-related information processing in the circuitry still remain poorly understood. In my talk, I will summarize recent results demonstrating flexible encoding and consolidation of reward-related information at the ensemble level and cellular level in the hippocampus. These studies identify a novel role for hippocampal sharp-wave ripple-related memory replay in promoting unbiased consolidation of informative cognitive maps of the world by adaptively selecting or excluding experimentally salient stimuli, including reward reinforcers. Frist, two-photon calcium imaging of CA3 axonal projections to CA1 combined with simultaneous local field potential recordings revealed that CA3 projections encoding behaviorally informative sensory stimuli were selectively recruited during the memory replay events that underlie hippocampal memory consolidation. These axonal projections formed sequential assemblies conjunctively linking sensory features to spatial location and thus reward proximity. By contrast, axons encoding uninformative, peripatetic sensory cues were notably suppressed during memory replay. In a second study, we used simultaneous fast calcium imaging and electrophysiology to track hippocampal are CA1 place cells over two weeks of online spatial reward learning behavior and offline resting. We describe that recruitment to persistent network-level offline reactivation of spatial experiences in mice predicts the future representational stability of place cells days in advance of their online reinstatement. Moreover, while representations of reward-adjacent locations are generally more stable across days, offline-reactivation-related stability is, conversely, most prominent for reward-distal locations. Lastly, I will introduce results suggesting that reward-related and context-related information are preferentially conveyed to the hippocampus from respective lateral and medial entorhinal cortical inputs during goal-directed navigation and learning. Together these provide significant new insights into reward-related information encoding and consolidation in the hippocampal-entorhinal circuitry. | |
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