Surge of neurophysiological coherence and connectivity in the dying brain.

During cardiac arrest, the mammalian brain can generate a transient surge of highly coherent gamma oscillations that exceed levels seen during conscious waking. In rats undergoing experimental cardiac arrest, continuous electroencephalography revealed a global increase in gamma power, coherence, and directed connectivity within the first 30 seconds after arrest, before the electroencephalogram became isoelectric. These gamma waves were tightly phase-coupled to theta and alpha waves. The findings suggest that near-death, the brain can paradoxically produce neural correlates of heightened conscious processing.

Study at a glance

Abstract

The brain is assumed to be hypoactive during cardiac arrest. However, the neurophysiological state of the brain immediately following cardiac arrest has not been systematically investigated. In this study, we performed continuous electroencephalography in rats undergoing experimental cardiac arrest and analyzed changes in power density, coherence, directed connectivity, and cross-frequency coupling. We identified a transient surge of synchronous gamma oscillations that occurred within the first 30 s after cardiac arrest and preceded isoelectric electroencephalogram. Gamma oscillations during cardiac arrest were global and highly coherent; moreover, this frequency band exhibited a striking increase in anterior-posterior-directed connectivity and tight phase-coupling to both theta and alpha waves. High-frequency neurophysiological activity in the near-death state exceeded levels found during the conscious waking state. These data demonstrate that the mammalian brain can, albeit paradoxically, generate neural correlates of heightened conscious processing at near-death.