Irreversible flux in hippocampal neural activity induced by physical navigation

Establish whether directed physical movement of a mouse along a one-dimensional track induces an irreversible cycle of probability flux in the abstract state space of hippocampal population activity, where states are defined by the most recently firing neuron and transitions are measured at a fixed time delay.

Background

The authors analyze two-photon calcium imaging recordings from 1,485 hippocampal neurons while a mouse navigates a virtual linear track. Place cells in the hippocampus are known to fire preferentially at specific locations, implying a spatially structured neural representation.

They define neural states by the identity of the most recently firing neuron and transitions by subsequent spikes after a time delay. Before presenting results, they point out that it is not established whether the physical forward movement (which creates an irreversible cycle in physical space) leads to an irreversible flux in the neural activity state space. Their subsequent analysis uses coarse-graining to reveal macroscopic flux loops consistent with navigation, but the initial question delineates the uncertainty motivating the paper.