Ephaptic Coupling and Regular Firing Optimize Tactile Signal Transmission in the Dorsal Column

Low-threshold mechanoreceptors (LTMRs) exhibit diverse firing patterns during tactile exploration, with responses varying depending on stimulus properties. For example, slowly adapting type 1 (SA1) afferents can display irregular firing during sustained indentation but shift to a regular pattern under vibratory stimulation. These dynamic firing modes may influence how tactile signals are propagated along sensory pathways. In this study, we employed a biophysically detailed computational model of ephaptic coupling to investigate how different firing patterns affect conduction velocity and spike-time synchronization as LTMR axons transition from the cellular heterogeneity of the peripheral nerve to the more homogeneous composition of the dorsal column. Our simulations demonstrate that regular firing patterns enable the fastest and most temporally precise spike propagation by serving as a pacemaker for phase-locking other patterns. These results suggest that the cellular homogeneity of the dorsal column may optimize tactile signal transmission via ephaptic coupling, providing a mechanism for synchronizing diverse peripheral inputs before they reach supraspinal targets.