Layer-Specific Contributions to Priming of Pop-Out Effects in Macaque Cortex: An LFP Power and Functional Connectivity Analysis

Abstract

Investigating the effects of priming of pop-out in the visual cortex offers valuable insights into neural processing because it can reveal the dynamics of how the cortex handles sensory information. The primary objective of this research was to explore the processing of information in macaque’s visual cortical area V4 during priming of pop-out in a visual search task and examine whether there were differences compared to unprimed settings. V4 can be organised in supragranular, granular and infragranular layers, each being differently involved in information processes within V4 or between other areas of the brain. The analysis utilised local field potential (LFP) signals recorded from this area of two macaque’s cortex in 27 sessions, using laminar electrodes across 15 channels covering the entire range of cortical layers. This allowed the sampling of different groups of neurons in each session and a layer-specific analysis in V4. Power, phase synchronisation, and information flow dynamics across layer levels in both primed and unprimed states were investigated. Phase synchronisation between cortical layers was measured by calculating pairwise phase coherence, phase locking values (PLV), phase lag indices (PLI) and pairwise phase consistency (PPC) in the frequency band filtered LFP signals, and information flow dynamics were investigated by applying pairwise Granger causality analysis on the LFP signals of the cortical layers. The results showed a difference in power between unprimed and primed trials across cortical layers, highlighting altered information processing in primed visual tasks and a possible facilitation effect. No notable differences in phase synchronisation and functional connectivity between unprimed and primed settings were observed, suggesting that the underlying coordination between the cortical layers remains consistent and more local within layers.