The Local Field Potential Reflects Surplus Spike Synchrony

TL;DR

This study shows that surplus spike synchrony during specific time intervals enhances the local field potential (LFP) and suggests a dual coding scheme of rate and synchrony in cortical processing.

Contribution

It provides experimental evidence linking transient spike synchrony to LFP dynamics and introduces a quantitative model explaining this relationship.

Findings

Surplus spike synchrony enhances LFP entrainment.

Large LFP amplitudes amplify synchrony effects.

Neurons participate in different constellations with partial spike contribution.

Abstract

The oscillatory nature of the cortical local field potential (LFP) is commonly interpreted as a reflection of synchronized network activity, but its relationship to observed transient coincident firing of neurons on the millisecond time-scale remains unclear. Here we present experimental evidence to reconcile the notions of synchrony at the level of neuronal spiking and at the mesoscopic scale. We demonstrate that only in time intervals of excess spike synchrony, coincident spikes are better entrained to the LFP than predicted by the locking of the individual spikes. This effect is enhanced in periods of large LFP amplitudes. A quantitative model explains the LFP dynamics by the orchestrated spiking activity in neuronal groups that contribute the observed surplus synchrony. From the correlation analysis, we infer that neurons participate in different constellations but contribute only a fraction of their spikes to temporally precise spike configurations, suggesting a dual coding scheme of rate and synchrony. This finding provides direct evidence for the hypothesized relation that precise spike synchrony constitutes a major temporally and spatially organized component of the LFP. Revealing that transient spike synchronization correlates not only with behavior, but with a mesoscopic brain signal corroborates its relevance in cortical processing.