Hippocampal Sequences and the Cognitive Map

Abstract

Ensemble activity in the hippocampus is often arranged in temporal sequences of spiking. Early theoretical and experimental work strongly suggested that hippocampal sequences functioned as a neural mechanism for memory consolidation, and recent experiments suggest a causal link between sequences during sleep and mnemonic processing. However, in addition to sleep, the hippocampus expresses sequences during active behavior and moments of waking rest; recent data suggest that sequences outside of sleep might fulfi ll functions other than memory consolidation. These fi ndings suggest a model in which sequence function varies depending on the neurophysiological and behavioral context in which they occur. In this chapter, we argue that hippocampal sequences are well suited to play roles in the formation, augmentation, and maintenance of a cognitive map. Specifi cally, we consider three postulated cognitive map functions (memory, construction of representations, and planning) and review data implicating hippocampal sequences in these processes. We conclude with a discussion of unanswered questions related to sequences and cognitive map function and highlight directions for future research.

Hippocampal replays under the scrutiny of reinforcement learning models

“…These MB-RL inference methods also have the potential of generating imaginary sequences, because the reactivations they produce are not constrained to previously experienced sequences, in contrast to MF-RL replays. Therefore, the experimental observation of hippocampal replays that go beyond the animal's past experience, such as hippocampal sequences suggesting an unexperienced combination of paths within the maze (Gupta et al 2010), have so far only been explained in terms of MB-RL, rather than MF-RL, and more specifically in terms of cognitive maps (Wikenheiser and Redish 2015). Our simulations confirm this MB-RL explanation of imaginary replays.…”

An Embodied Agent Learning Affordances With Intrinsic Motivations and Solving Extrinsic Tasks With Attention and One-Step Planning

“…Later, forward planning became popular again, thanks to general-purpose heuristics that allowed the reduction of the search breadth based on domain-independent general heuristics, for example focusing only on the “positive effects” (usually denoting the action success) while ignoring the “delete effects” (usually involved in the violation of other sub-goals). This suggests that the common use of forward planning by organisms (Wikenheiser and Redish, 2015) might rely on affordances for pruning relevant actions: affordances hence are so important for organisms (Thill et al, 2013) because they not only support an efficient action but also planning.…”