Non‑monotonic reorganization of cortical neuron firing despite ongoing delta‑dominated activity

Abstract

Delta - dominated activity is a hallmark of anesthesia and non‑REM sleep, yet how neuronal firing evolves across these rhythms remains unclear. Here, by tracking cortical neuron firing in the ketamine‑xylazine model, we find that across continuing delta - dominated activity, population firing rates progress through successive epochs of excitation, suppression, and re - emergence. Concurrently, fine‑scale spike timing and burst dynamics exhibit non - monotonic modulation, revealing continuous reorganization beneath the ongoing delta-dominated oscillation. At the transition to theta - dominated activity, a restructuring of temporal patterning without a significant shift in the firing - rate distribution suggests that temporal structure, rather than firing rate, defines this transition. These population - level dynamics were firing - rate - dependent: high‑firing - rate neurons were more tightly modulated, whereas low‑firing-rate neurons exhibited more heterogeneous changes. Neither ketamine nor xylazine alone recapitulates these dynamics, suggesting their combined action creates a uniquely dynamic architecture. These findings reveal a continuous, firing - rate - dependent reorganization of single-neuron activity during ongoing delta-dominated states.