Hippocampal information processing between subregions is responsible for episodic learning, recall, and spatial navigation yet difficulties accessing spikes in interregional axons impede detailed understanding. Our lab has reconstructed the trisynaptic loop in vitro with isolation of axons in microfluidic channels to access spiking information between subregions. The axonal spiking dynamics and how they relate to somal activity with electrical stimulation provide insight on the information processing and routing principles in the hippocampus as well as the critical dynamic balancing of network activity. Resting differences in slopes of the log-log distributions of inter-spike intervals, interburst intervals and spikes per burst suggest quasi-critical behavior that shifts to subcritical after stimulation. Thus, the dynamics balance to accommodate stimulation. Increases in feedback over feedforward signaling were associated with stimulation, especially in axon spiking from the EC back to the CA1. By graph analysis of well-tunnel spike rate correlations with stimulation, the network shifts to more feedback activity over feedforward, and an overall decrease in routes (edges), but an increase in reliability centrality (importance), i.e., route sharpening. Characterizing the range over which the hippocampal subregions homeostatically balance activity around the quasicritical point for optimization of information processing could aid applications in computational technologies.

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