Ephaptic coupling can explain variability in neural activity.

The waxing and waning cortical oscillatory power correlates with function and disease. This cross-trial variability has been thought to be due to neuromodulation, uncertainty encoding, and/or changes in cortical excitability. Here, we report evidence that it is also due to fluctuations in ephaptic influences of mesoscale electric fields. We analyzed LFP data from the PFC recorded during a spatial delay saccade task. We constructed a model that describes the electric field close to the cortical patch given the neural activity that generates it. This revealed that field-to-neuron interactions (ephaptic coupling strength) were stronger than neuron-to-field, and it correlated trial-by-trial changes in oscillatory power. This suggests a form of circular causality where neural activity and extracellular electric fields continuously shape each other. These results further suggest that mesoscale ephaptic effects help drive the formation of memory ensembles, a prediction of the cytoelectric coupling hypothesis.