What happens after we die? That’s a question the living among us will never be able to answer. But as for what happens when we die, that’s a conundrum scientists may be a step closer to solving.

Researchers observing the brains of dying patients have reported a surge in activity similar to that seen while dreaming and in seizure patients during hallucinations and ‘out of body’ experiences.

The study may help explain the ‘near-death’ experiences reported by up to a fifth of cardiac arrest survivors, regardless of cultural or religious background.

A team from the University of Michigan analysed heart and brain function using electrocardiogram (ECG) and electroencephalogram (EEG) signals in four comatose patients after the withdrawal of ventilatory support. 

Two of the patients showed a rapid rise in an area of the brain known as the ‘hot zone’, which is thought to be critical for conscious processing. The increase in gamma waves detected by the EEG was stimulated by global hypoxia – the complete lack of oxygen after ventilation was removed – while their heart rate also increased.

Writing in The Proceedings of the National Academy of Sciences, the team said: ‘Internal perception of bright light or familiar faces reported by survivors of clinical death suggests a preserved capacity in the dying brain to process internally generated vision.’

In short, the moments before death may be more vivid than a simple fading into black.

The team, led by Dr Jimo Borjigin, investigated whether the gamma activity could have been due to the patients suffering seizures as a result of the lack of oxygen, but other EEG data showed no evidence to support the theory – although both patients had previously suffered seizures in their lifetimes.

However, the team is keen to stress the results do not prove any form of thought or consciousness at the point of death, because the patients did not survive to report their experiences.

‘How vivid experience can emerge from a dysfunctional brain during the process of dying is a neuroscientific paradox,’ said co-author Dr George Mashou. ‘Dr Borjigin has led an important study that helps shed light on the underlying neurophysiologic mechanisms.’

All four patients in the study had been determined beyond medical help. Their families granted permission for the removal of life support.

Dr Nusha Mihaylova, who collaborated with Dr Borjigin on the work and collected EEG data for the study, added: ‘We are unable to make correlations of the observed neural signatures of consciousness with a corresponding experience in the same patients in this study. 

‘However, the observed findings are definitely exciting and provide a new framework for our understanding of covert consciousness in the dying humans.’

Previous studies in animals have also demonstrated high levels of gamma wave activity before death.

‘Empirical evidence presented in this study strongly suggests that the dying human brain can be activated,’ the team concluded. 

‘This study lays the foundation for further investigation of covert consciousness during cardiac arrest, which may serve as a model system to explore mechanisms of human consciousness.’

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