Large-scale infra-slow dynamics of extracellular potentials linked to synchronous states revealed by graphene neural probes

Infra-slow (<0.5 Hz) brain dynamics reflect homeostatic and neuromodulatory processes that modulate neuronal excitability and shape faster oscillations across brain regions. Infra-slow brain activity is typically inferred from magnetic or optical imaging, but these methods are limited in temporal resolution and compatibility with unconstrained behavior. Infra-slow local field potentials (isLFPs) could provide a direct measure of infra-slow network dynamics, but have remained poorly characterized due to the absence of scalable, DC-coupled recording methods. Here, we introduce DC-coupled electrophysiological imaging based on arrays of up to 512 multiplexed graphene transistors enabling stable, high-density recordings across cortical regions and cortical layers in freely moving rats. We developed an analytical framework for the analysis of wide-band LFP, revealing that synchronous oscillatory states of variable duration and spatial scale are consistently linked to topographically and translaminarly structured DC potential shifts. We propose a physiological model linking these DC shifts to sustained gradients of extracellular K+ concentration, providing a mechanistic connection between neuronal synchrony and isLFP dynamics. By integrating DC-coupled sensing, multiplexed scalability, and depth-surface co-registration, this work establishes a new modality for imaging-like electrophysiology in freely moving animals and a framework for interpreting infra-slow dynamics.