Some people are able to achieve astral travel – an out-of-body experience, without the use of a psychoactive substance, with the help of certain mental instructions and mental techniques that they find in literature or on the Internet. In percentage terms, this is a small fraction of people, not even one percent of people who can do it. These people are also mentally healthy – they do not suffer from any mental disorder – at least the vast majority of them (although some schizophrenics may also have out-of-body experiences).
These people may naturally have a different level of activity of some receptors in the brain than most people. The brain of such people may work similarly to when a normal person is under the influence of a psychoactive substance. This may involve high activity of dopamine, serotonin and κ (kappa) opioid receptors, sigma receptors and low activity of NMDA receptors.