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arXiv · 2305.08124

Theta sequences as eligibility traces: a biological solution to credit assignment

Tom M George
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Abstract

Credit assignment problems, for example policy evaluation in RL, often require bootstrapping prediction errors through preceding states \textit{or} maintaining temporally extended memory traces; solutions which are unfavourable or implausible for biological networks of neurons. We propose theta sequences -- chains of neural activity during theta oscillations in the hippocampus, thought to represent rapid playthroughs of awake behaviour -- as a solution. By analysing and simulating a model for theta sequences we show they compress behaviour such that existing but short $\mathsf{O}(10)$ ms neuronal memory traces are effectively extended allowing for bootstrap-free credit assignment without long memory traces, equivalent to the use of eligibility traces in TD($\lambda$).

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Tom M George. 2023-05-14. Theta sequences as eligibility traces: a biological solution to credit assignment. https://arxiv.org/abs/2305.08124

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