The study, led by Jimo Borjigin, associate professor of molecular and integrative physiology and neurology at Michigan, was very small, featuring only four patients. But the findings echo animal model studies, where the presence of gamma waves in dying brains has also been observed, including in a previous study in rats that Borjigin and colleagues ran a decade earlier.

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“These data demonstrate that the surge of gamma power and connectivity observed in animal models of cardiac arrest can be observed in select patients during the process of dying,” the researchers wrote in their paper, published in PNAS.

What are gamma waves? Gamma waves are high-frequency brain waves researchers believe represent multiple areas of the brain working together in complex thoughts. Take, for example, combining the sight, sound, and smell of a car to get a full picture of the vehicle, Ajmal Zemmar, a neurosurgeon at the University of Louisville uninvolved with the study, told Science.

Researchers have also found patterns of gamma waves in healthy people while dreaming, learning, and recalling lessons, Science reported, with some researchers associating them with consciousness itself. But the exact mechanisms behind gamma waves are “one of the biggest mysteries in neuroscience,” Zemmar said.