A recent study by Jimo Borjigin and colleagues (University of Michigan) reports that highly coherent, global oscillations in the brains of rats occurred from about 12 to 30 seconds after cardiac arrest. The investigators found that near death, some of the electrical signatures of consciousness exceeded levels found in the waking state, providing "strong evidence for the potential of heightened cognitive processing in the near-death state." "The measureable conscious activity is much, much higher after the heart stops." They assert that this evidence provides "a scientific framework to begin to explain the highly lucid and realer-than-real mental experiences reported by near-death survivors."
How well do these assertions hold up to scrutiny?
Commentary by Robert Mays, NDE researcher
There are three major flaws in the reasoning that the University of Michigan researchers used. The first flaw is that a near-death experience, with its elements of the sense of being out of the body, feelings of peace, hyper-real lucid sensations and mentation, and so on, occurs only when an individual is near death. It's important that any explanation of the phenomenon of NDEs explain the broad spectrum of cases in which they occur. NDEs can be triggered by cardiac arrest or a physical trauma, but they can also be triggered by an accident in which the NDEr is not hurt and even in a healthy individual who experiences an NDE spontaneously.
Furthermore, shared-death experiences provide even further evidence where a healthy person at the bedside of a dying loved one experiences many of the same elements of the NDE (see Moody and Perry, Glimpses of Eternity, 2010).
There is no physiological explanation of NDEs and SDEs that can explain the variety of trigger conditions and elements of the experience. So while the results of Dr. Borjigin and colleagues are interesting, they do not provide a scientific framework for explaining NDEs.
The second major flaw in reasoning has to do with the assumption that coherent oscillations in widely separated regions in the brain constitute a general signature of consciousness. In fact, coherent oscillations are neural correlates of consciousness, but are specific to cognitive activity that is directed toward a particular task such as visual spatial attention or directed motor activity. The oscillations tend to be transient, lasting only a few hundreds of milliseconds and the brain regions involved are related to the cognitive task at hand.
In fact the transient pattern of coherent gamma oscillations (25-55 Hz) that were observed in the awake rats in this study prior to anesthesia is typical of consciousness. The coherent oscillations are only a small part of the overall picture of the rat's consciousness. Coherent gamma oscillations are indications only of specific, directed cognitive activity rather than general consciousness. These oscillations always occur in the context of other electrical activity that indicate general consciousness. Thus the result that the gamma oscillations increased significantly in the period after cardiac arrest is not an indication of a heightened general consciousness.
Finally, the third major flaw is that the researchers discounted or ignored the overall power of the electrical activity in the awake rat, where there is clearly consciousness, compared with the greatly reduced power of electrical activity after cardiac arrest. The overall power of electrical activity in the conscious rat is more than 30 times greater than after cardiac arrest. (This is an estimate since I do not have access to the specific data).
There is ample evidence that consciousness is supported only by a certain minimal level of electrical activity. After the cardiac arrest, the rats do not have sufficient electrical brain activity to support consciousness. This conclusion is consistent with EEG studies in humans who experienced cardiac arrest and who immediately lost consciousness.
So what do the highly coherent, global oscillations in the rats indicate? Most likely they are a natural oscillation that occurs in resonant neural circuits when the neural activity of the living rat has ceased. In other words, they are the remnant electrical activity of a dead brain.