Canadian researchers studying the neuroscience of the moment of death ('necroneuroscience') have uncovered a surprising phenomenon: anomalous EEG activity up to 10 minutes after the time of clinical death. The researchers were examining EEG readings recorded at the time that life support was withdrawn from four critically ill patients, and found that in one of patients - a 67-year-old man who suffered cardiac arrest - "single delta wave bursts persisted following the cessation of both the cardiac rhythm and ABP":
It is difficult to posit a physiological basis for this EEG activity given that it occurs after a prolonged loss of circulation. These waveform bursts could, therefore, be artefactual in nature, although an artefactual source could not be identified.
Here's the EEG readings of the four patients:
On the other hand, it's worth noting also that this study failed to find evidence for the so-called 'death wave' previously found in studies with rats, in which a surge of brain activity was detected at the time of death, leading some people to suggest that it might evidence for a 'near-death experience' type brain event.