Brain wave synchronization, also called neuronal coherence, is a fundamental mechanism of communication in the brain, where synchronized field potentials coordinate synaptic and spiking events to support plasticity and learning. Although the spread of field potentials has garnered great interest, little is known about the spatial reach of neuronal coherence. Here we used simultaneous recordings from electrocorticography grids and high-density microelectrode arrays to estimate the spatial reach of neuronal coherence and spike-field coherence (SFC) across frontal, temporal, and occipital cortices during cognitive tasks in humans. We observed the strongest coherence within a 2-3 cm distance from the microelectrode arrays, potentially defining an effective range for local communication. This range was consistent across brain regions, frequencies, and cognitive tasks. The magnitude of coherence showed power law decay with increasing distance from the microelectrode arrays, where the highest coherence occurred between ECoG contacts, followed by coherence between ECoG and deep cortical LFP, and then SFC (ECoG > LFP > SFC). The spectral frequency of coherence also affected its magnitude. Alpha coherence was generally higher than other frequencies for signals nearest the microelectrode arrays, whereas delta coherence was higher for signals that were farther away. Action potentials in all brain regions were most coherent with the phase of alpha oscillations, which suggests that alpha waves could play a larger, more spatially local role in spike timing than other frequencies. These findings provide a deeper understanding of the spatial and spectral dynamics of neuronal coherence, further advancing knowledge about how activity propagates across the human brain.

Learning Objectives:

1.    Describe the underlying nature of brain waves.

2.    Explain the importance of brain wave synchronization to cognition and behavior.

3.    Identify factors that play a role in how synchronization spreads across the brain.