Neuroscience and the near-death experience: roles for the NMSA-PCP receptor, the sigma receptor and the endopsychosins.

The Near-Death Experience (NDE) is a dissociative mental state with characteristic features. These can be reproduced by ketamine which acts at sigma sites and blocks N-methyl-D-aspartate (NMDA) linked phencyclidine (PCP) receptors to reduce ischaemic damage. Endogenous ligands, alpha and beta-endopsychosin, have been detected for these receptors which suggests an explanation for some NDE's: the endopsychosins may be released in abnormal quantity to protect neurons from ischaemic and other excitotoxic damage, and the NDE is a side effect on consciousness with important psychological functions.