Optogenetic inhibition of the rodent dorsal hippocampus impairs temporal duration sequence memory retrieval
Zhemeng Wu1 (firstname.lastname@example.org), Sandeep Dhawan1, Nisma Khan1, Andy Lee1, Rutsuko Ito1; 1University of Toronto Scarborough
Convergent animal and human research have demonstrated that the hippocampus represents timing information embedded within a sequence of events. However, the specific roles of hippocampal subdivisions remain unclear. We developed a novel cross-species behavioural task to examine the temporal acquisition process using a novel computation modelling and then investigated the role of rodent dorsal hippocampus (dHPC) in temporal duration memory after acquisition. Across a number of training days, Long Evans rats learned to identify, via a left/right lever press, two distinct auditory sequences, each comprised of a pure tone and white noise of differing durations. We then developed a computational model to characterize the temporal learning dynamics of each participant and to identify the source of inter-participant variability. This model comprised of two components: (1) Bias, a cubic spline function captured the extent to which a subject’s responding is biased towards one lever in the early phases of learning; and (2) Learning, a sigmoid function was implemented to provide insight into each subject’s learning process. We found that although rats were able to successfully learn the different sequences, they demonstrated different strategies: some rats acquired both sequences equally throughout learning while others were biased towards learning one sequence over the other early on. After successful sequence acquisition, we inhibited the dorsal hippocampus (dHPC) using optogenetics. dHPC inhibition during sequence presentation impaired performance while inhibition during choice phase had no impact. Our data suggest a critical role for the rodent dHPC in representing temporal duration information in the context of sequences.
Topic Area: LONG-TERM MEMORY: Episodic
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