ScienceDaily (here) and (in more detail) a blog by Ed Yong (here) discuss a paper by Jimo Borjigin and others; “Surge of Neurophysiological Coherence and Connectivity in the Dying Brain” in PNAS. The paper is about near-death experiences.
Here is the 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.
The neural correlates of consciousness are synchronized gamma waves connecting distant parts across the cortex together and involving a loop with the thalamus. What they seem to have found is a short period strong synchronized gamma waves, indicating consciousness during the first half second of cardiac arrest, with strong coupling to theta and alpha waves – a super level of consciousness fitting with the very vivid memories of near-death experiences in humans.
There are still questions of what the mechanism is for this burst of conscious activity. Is something being released by the brain cells as they die that enhances activity for a short period? Is some brake on extreme activity released? Is the brain actually (unlikely as it may be) trying to think a way out of death? Is there an attempt to re-establish a balance that is disappearing?
Of course, some people have found it hard to accept that rats might have near-death experiences, or that near-death experiences could be explained as brain activity with no super-natural cause. But, that is to be expected. Near-death experiences were one of the only refuges left for the idea of a form of consciousness that could be independent of the body.