CONVERGENCE OF HIPPOCAMPAL NEURAL SEQUENCES PRODUCES A COMPRESSED SPACE OF REMEMBERED EXPERIENCE

Highly reliable sequential dynamics organize neural activity in the hippocampus and progress with changes in physical, sensory, or cognitive variables, typified by place cells during active exploration. But sensory and behavioral variables are often confounded, and so it remains intensely debated whether hippocampal sequences are driven by sensory content directly or rather reflect the alignment of internally generated dynamics to external perception.
Here we used mouse virtual reality to characterize hippocampal dynamics in environments with systematically different sensory complexity, and to test the robustness of neural sequences to manipulations of precise sensory content. The structure of neural sequences could be perturbed by changes in both moment-to-moment visual experience and ongoing behavior, a pattern that was best explained by the different behavioral strategies employed by the animal in the presence or absence of sensory ambiguity. Neural subsequences could be flexibly interrupted, inserted, and resumed wherever a memory of prior experience was violated, indicating that the propagation of hippocampal dynamics was not rigidly fixed by internal networks and initial conditions. Our results are congruent with hippocampal computations that organize experience along an abstract memory space, which can flexibly encompass both sensory and internal factors according to the selective and variable memory demands encountered by the animal across contexts.