Serotonin and the Mystic Potential
A 2003 study The Serotonin System and Spiritual Experiences published in The American Journal of Psychiatry reveals an interesting correlation between Serotonin receptor density in the brain and the capacity for spiritual experiences. Given the limitations, the results of this study must be interpreted with caution; however this may reveal insight into the biology behind the fact that not everyone is capable of mystic experiences.
And of course, it would be erroneous to interpret this study as demonstrating that mystic experiences are 'all in the head'. The study proves no such thing.
"In the present study, we found an association between interindividual variability in 5-HT1A receptor binding potential and the self-transcendence score on the Temperament and Character Inventory. We found no correlation for any of the other dimensions. The lack of correlation for the other dimensions is consistent with a previous study that used Tridimensional Personality Questionnaire, and an earlier questionnaire covering the four temperament dimensions of the Temperament and Character Inventory.
The self-transcendence dimension is the most stable Temperament and Character Inventory dimension over time and is also one of the two Temperament and Character Inventory dimensions showing the largest variability. The self-transcendence dimension consists of three subscales representing several aspects of religious behavior, subjective experience, and individual worldview. Of interest, in the extended analysis, we found that the correlation of self-transcendence was shown to be fully dependent on the spiritual acceptance scale, whereas no correlation was found to the other two subscales. (My emphasis)
The spiritual acceptance scale measures a person’s apprehension of phenomena that cannot be explained by objective demonstration. Subjects with high scores tend to endorse extrasensory perception and ideation, whether named deities or a commonly unifying force. Low scorers, by contrast, tend to favor a reductionistic and empirical worldview.
A role for the serotonin system in relation to spiritual experiences is supported by observations of drugs such as LSD, psilocybin, N,N-dimethyltryptamine, mescaline, and 3,4-methylenedioxymethamphetamine that are known to cause perturbations of the serotonin system in several brain regions.
On a behavioral level, these drugs elicit perceptual distortions, illusions, a sense of insight, spiritual awareness, mystical experiences, and religious ecstasy. Of interest, such pharmacological effects induced by hallucinogens resemble the extrasensory perception and ideation endorsed by subjects scoring high on the spiritual acceptance scale.
However, another drug causing spiritual experiences is salvatorin A. This drug may act primarily on the kappa opioid receptor system, indicating that the serotonin system is not the only brain neurotransmitter system that may be related to spiritual experiences."