In 1975, scientists Robert Ader and Nicholas Cohen demonstrated classic conditioning of the immune function in their experiments with rats at the University of Rochester. In the process the coined the term “psychoneuroimmunology.” (Ader & Cohen, 1975 The experiment demonstrated that the nervous system ― and even our thoughts ― can influence the immune system. Scientists formerly believed that each physical system functioned independently.

Another breakthrough showing neuro-immune interactions occurred years later, in 1981 when Indiana University of Medicine scientist David Felten found nerves connected to blood vessels and cells of the immune system, as well as in the thymus and spleen ending at clusters of immune function-regulating lymphocytes, macrophages and mast cells. Combining their research, Ader, Cohen and Felten edited Psychoneuroimmunology in 1981, proposing that the brain and immune system work together to keep the body healthy.

Following suit, in 1985 neuropharmacologist Candace Pert at Georgetown University demonstrated that the cell walls and the brain have neuropeptide-specific receptors. (Pert et al.; Ruff et al. 1985) This research provided scientific proof that emotions and immunity are interrelated.

According to Steven Maier, Ph.D., the body can translate a blood-borne signal into a neural signal. Maier explained the importance and relevance of the vagus nerve in transmitting information to the brain. This nerve acts as an immunomodulator, regulating the production of pro-inflammatory cytokines.

Maier explains that the blood-brain barrier does not allow cytokines produced by the macrophages to cross. Instead, the vagus nerve translates the information for the brain. In the next post, we’ll see how this system works.