Spatiotemporal patterns of sub-threshold oscillatory activity in the inferior convexity of the macaque prefrontal cortex
Despite significant progress in understanding functional parcellation of the primate prefrontal cortex (PFC) it is currently unknown whether an intrinsic mechanism could dynamically coordinate activity between these functionally specialized sub-regions. Such a mechanism could be reflected in spatially organized rhythmic activity that is mesoscopically observed as complex, rhythmic spatio-temporal patterns. In order to identify such spatio-temporal patterns in the default state of the prefrontal cortical network we recorded from the inferior convexity of the macaque PFC during anesthesia using multi-electrode (Utah) arrays. The power spectrum and spatial coherence of oscillatory activity exhibited a distinctive peak in the beta (15-30 Hz) frequency range of local field potentials (LFP's) during resting state but also during sensory stimulation with dynamic movie stimuli, revealing a dominant rhythm in the PFC. We observed consistent phase gradients in the beta band that formed complex, dynamic patterns, suggesting propagation of oscillatory activity across the cortical surface. These spatio-temporal patterns were subsequently clustered using a graph cut algorithm based on a measure of phase shift invariant similarity. Our analysis revealed a dominant travelling wave pattern in the beta band, propagating along the ventral-dorsal plane and replaced by less frequent, less dominant patterns both in the absence of visual stimulation (spontaneous activity) and during stimulation with movie clips. By estimating mutual information, we found that the amplitude of this wave conveyed sensory information during the presentation of several movies. These findings suggest that spatiotemporal phenomena are suggestive of highly coordinated activity in the PFC, a cortical area known to be involved in associative functions. In particular, traveling waves of oscillatory neural activity are modulated by sensory input and could provide a functional substrate for coordinating activity across different subregions of the PFC.