Memories are extremely fallible

Dr Chris Freeman, Royal Edinburgh Hospital

Of these 56 had no recollection of the period of unconsciousness they experienced whilst, effectively, clinically dead.

However, seven had memories, four of which counted as near-death experiences.

They told of feelings of peace and joy, time speeded up, heightened senses, lost awareness of body, seeing a bright light, entering another world, encountering a mystical being and coming to "a point of no return".

Oxygen levels

None of the patients were found to be receiving low oxygen levels - which some scientists believe may be responsible for so-called "near-death" experiences.

Lead researcher Dr Sam Parnia, of Southampton General Hospital, said nobody fully understands how brain cells generate thoughts.

He said it might be that the mind or consciousness is independent of the brain.

He said: "When we examine brain cells we see that brain cells are like any other cells, they can produce proteins and chemicals, but they are not really capable of producing the subjective phenomenon of thought that we have.

"The brain is definitely needed to manifest the mind, a bit like how a television set can take what essentially are waves in the air and translate them into picture and sound."

Scepticism

Dr Chris Freeman, consultant psychiatrist and psychotherapist at Royal Edinburgh Hospital, said there was no proof that the experiences reported by the patients actually occurred when the brain was shut down.

"We know that memories are extremely fallible. We are quite good at knowing that something happened, but we are very poor at knowing when it happened.

"It is quite possible that these experiences happened during the recovery, or just before the cardiac arrest. To say that they happened when the brain was shut down, I think there is little evidence for that at all."