A discussion like this automatically turns into a debate between those who are materialists and believe there is nothing beyond the physical universe and those who believe there is.
There is at least one study that might bear on this although from a clinical view it did not measure brain waves which would be seriously hard to do with current technology:
[Cardiac arrest] survivors commonly experience a broad range of cognitive themes, with 2% exhibiting full awareness. This supports other recent studies that have indicated consciousness may be present despite clinically undetectable consciousness. This together with fearful experiences may contribute to PTSD and other cognitive deficits post CA.
http://www.resuscitationjournal.com/article/S0300-9572(14)00739-4/fulltext
There is at least one study that might bear on this although from a clinical view it did not measure brain waves which would be seriously hard to do with current technology:
[Cardiac arrest] survivors commonly experience a broad range of cognitive themes, with 2% exhibiting full awareness. This supports other recent studies that have indicated consciousness may be present despite clinically undetectable consciousness. This together with fearful experiences may contribute to PTSD and other cognitive deficits post CA.
http://www.resuscitationjournal.com/article/S0300-9572(14)00739-4/fulltext