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Summary

Loss of consciousness under anaesthesia is accompanied by widespread silencing of neurons, and disruption of cortical dynamics. Yet, how this affects mesoscale signal propagation within higher-order associative areas, crucially implicated in theories of consciousness, remains poorly understood. Here we combined intracortical microstimulation, and simultaneous multielectrode recordings in the ventrolateral prefrontal cortex (vlPFC) and the posterior parietal cortex (PPC) of macaques across wakefulness, and graded depths of anaesthesia. Spiking responses revealed distinct regimes: in the PFC, higher-amplitude stimulation elicited a delayed single rebound after sustained inhibition, whereas in the PPC, a faster and double-rebound profile emerged. Despite enhanced local spiking and LFP responsivity under anaesthesia, we found a strong and selective suppression of lateral signal propagation in the PFC - a breakdown strikingly absent in the PPC. This dissociation suggests that anaesthesia disrupts consciousness not merely by silencing cortical populations, but by impairing mesoscale integrative processes critical for neuronal dynamics at multiple scales. Our findings demonstrate in a causal and spatially-resolved manner, that lateral signal spread within higher-order cortex is a key mechanism underlying conscious awareness, and its loss under anaesthesia.