Velocities of Hippocampal Traveling Waves Proportional to Their Coherence Frequency

Abstract

Cortical traveling waves, characterized by their spatial, temporal, and frequency attributes, offer insights into active regions, timing, frequency, and the direction of activity propagation. Recent evidence suggests that these waves directionality and spatiotemporal extent encode cognitive processes, yet the encoding mechanism related to their frequency remains unclear. We explore the hypothesis that coherence frequency dictates the velocity of wave propagation. Using nonlinear coherence analysis to compute propagation pathways among four local-field-potential signals collected along the human hippocampuss long axis, we present evidence that the coherence frequency of traveling waves encodes temporal communication aspects. Unlike linear analyses, which may overestimate velocities due to bidirectional flow when considering multiple pair coherences, nonlinear analysis treats pathways as holistic units with affectively unidirectional flow, making it more suitable for calculating wave velocities. Our findings reveal that propagation velocities along the hippocampus at low frequencies (<[~]35Hz) demonstrate a linear dependency on frequency, with an increased slope at higher frequencies, suggesting different underlying mechanisms. Although observed within the hippocampus, these findings capture a dependency between frequency and velocity of traveling waves which may be applicable to other cortical areas as well.