This got her thinking: What kinds of changes does the brain go through at the moment of death?
Last year, Borjigin turned to Mashour, a colleague with expertise in EEG and consciousness, for help conducting the first experiment to systematically investigate electrical brain activity after cardiac arrest. EEG uses electrodes to measure voltage fluctuations in the brain caused by many neurons firing at once. A normal, awake brain should show spikes of activity depending on what types of processing are going on; in a completely dead brain, it flat-lines.
When the heart suddenly stops, ongoing blood flow to the brain stops and causes death in a human within minutes. A likely assumption would be that, without a fresh supply of oxygen, any sort of brain activity would go flat. But after the rats went into cardiac arrest, Mashour and his colleagues saw the opposite.
"We saw a window of activity with certain signatures typically associated with conscious processing," said Mashour.
Those signatures include heightened communication among the different parts of the brain, actively seen in an awake state, but often lost during anesthesia. In the rats, this connectivity went above and beyond the levels seen during the awake state — which could possibly explain the hypervivid, "realer-than-real" perceptions reported close to death, said Borjigin.
Mashour speculates this integration coincides with consciousness while we work to process aspects of the world in different areas of the brain, like visual in one area and auditory in another.
"The brain kind of gets it all together so we have this unified, seamless experience," he said.
But there are many gray areas of consciousness — for instance, being under anesthesia or in a vegetative state or seizing — and scientists are still trying to pin down a clear-cut electrical marker of consciousness.