Maybe cats have nine lives, or maybe brain dead people aren't so dead.
Parts of the brain may still be active after a commonly used brain activity reading goes to a flat line, according to a study on cat brains published Wednesday in the online journal PLOS One.
The study came after Romanian doctors noticed odd electroencephalogram (EEG) activity in a patient who had lapsed into a coma while under the influence of anti-seizure medication.
Researchers at the Universite de Montreal put 26 cats under deep anesthesia and recorded their brain activity in the upper cortical regions and hippocampus. In all of the cats, a previously undocumented "ripple event" was evident in the hippocampus after EEG read-outs went "flat," indicating a silenced cortex. The results appeared to replicate what had been seen in the human patient, according to the study.
The findings could revive debate over the criteria for declaring a person "brain dead." In the U.S., two such flat-line readings 24 hours apart are necessary, along with other tests of brain function.
Researchers said their findings suggest that the brain can survive an extremely deep coma and that inducing such a state could help preserve some brain function that otherwise might cease, causing the brain to atrophy.
Scientists have been steadily probing the nature of brain activity at the border of death. Evidence of a sharp burst in brain activity after cardiac arrest suggest a neural explanation for anecdotes from patients who have recovered from near-death experiences, including a sensation of leaving the body, and deep memories flickering in dream-like fashion.
The most famous example of the phenomena turned into a best-selling book, "Proof of Heaven," in which a physician recounted the vivid imagery he experienced during a coma. Neurologists question whether the cortex was fully shut down and suggest these memory functions reflected activity in the brain, not a supernatural phenomenon.
Anecdotes of near-death imagery have varied by culture and changed significantly over time and correlate with the teller's religious iconography, skeptics note. Heavenly experiences, they suggest, are in the mind of the beholder.
A recent study using mice showed that brain activity after complete cardiac arrest does not gradually wane to zero but is distinguished by phases that include a burst of activity -- a phenomenon noted also by the Montreal team.