Serotonin Receptors May Be Linked to Spirituality

Why are some people ardent religious believers and others not? Why are some people predisposed to mystical experiences?

The answers may lie, at least in part, in the number of receptors for the nerve transmitter serotonin in the brain, suggests a provocative study published in the November 2003 American Journal of Psychiatry.

The investigation was conducted by Lars Farde, M.D., Ph.D., a professor of psychiatry at the Karolinska Institute and Hospital in Stockholm, and colleagues.

Many people would undoubtedly balk at the notion that their religious beliefs and spiritual experiences, or lack thereof, are dictated by their biology. Yet a twin and adoption study reported in the journal Science in 1990 suggested that genes may contribute as much as 50 percent to individual differences in religiosity. Yet if genes determine up to a half of people’s spirituality, how do genes program it? Farde and his coworkers decided to try to find out.

The Temperament and Character Inventory is a self-report questionnaire in which individuals rate themselves on the personality traits of novelty seeking, harm avoidance, reward dependence, persistence, self-direction, cooperativeness, and self-transcendence. The self-transcendence trait in turn reflects a religious outlook versus material rationalism. Persons who score high on the trait of self-transcendence tend to endorse extrasensory perception and ideas, whether in the form of named deities or a common unifying force.

LSD and other drugs that induce spiritual awareness, mystical experiences, and religious ecstasy, for example, are known to affect the serotonin neurotransmitter system in several brain regions.

So Farde and his colleagues administered the Temperament and Character Inventory to 15 mentally and physically healthy men aged 20 to 45. They also used PET scans to determine the number of nerve receptors for serotonin located in three areas of subjects’ brains. These areas—the dorsal raphe nuclei of the brainstem, the hippocampus, and the neocortex—are usually rich in serotonin receptors. They then assessed whether there was any connection between subjects’ scores on the personality trait of self-transcendence and the number of serotonin receptors in their brains.

The investigators found that the number of serotonin receptors correlated significantly and inversely with subjects’ scores for self-transcendence—the higher the score on self-transcendence, the fewer the number of receptors in all brain areas scrutinized.

In contrast, the investigators could find no significant correlations between other personality traits measured by the Temperament and Character Inventory and the number of serotonin receptors.

Thus, “the serotonin system may serve as a biological basis for spiritual experiences,” the researchers concluded.

But how might the serotonin system affect spirituality? “My favorite interpretation,” Farde told Psychiatric News, “is that the serotonin system regulates our perception and the variety of stimuli reaching our awareness. A person with a weak ‘sensory filter’ is used to various perceptions and may be more likely to accept religious world views.”

The study was funded by the Swedish Research Council.

Farde and his colleagues plan to conduct a similar study with women subjects.

The study, “The Serotonin System and Spiritual Experiences,” is posted online at http://ajp.psychiatryonline.org/cgi/content/full/160/11/1965?. ▪

Am J Psychiatry 2003 160 1965