For many years, the immune system has been thought of as a stand-alone, independent mechanism. However, more recently, numerous links have been found between neuroscience and the immune system. This relatively new field is known as psychoneuroimmunology (PNI). Although ordinary people have long believed that stress can make you ill or slow down recovery, until a few decades ago this was considered little more than an old wives’ tale in the medical community— despite many first-hand accounts linking, for example, stress to skin conditions, or cancer survival to the patient’s attitude and support network.

Robert Ader, the father of this field of study, made his breakthrough discovery quite by chance. He was working on variations of the Pavlov’s dogs experiment, feeding rats sweetened water and simultaneously injecting them with a harmful drug that suppresses the immune system. As predicted, the rats were conditioned to avoid the sweet water. Ader then stopped injecting the rats but continued to offer them the sugary solution. The rats continued avoided it—but intriguingly, some of them died. It seemed to him that not only had an avoidance response been conditioned, but the drop in immunity brought on by the drug was also somehow being conditioned such that the rats still died without receiving the drug. His subsequent studies showed that his hypothesis, although mocked in the scientific community, was indeed correct, and the door was opened for studies into the relationship between the central nervous system and the immune system.

As the field of PNI grows, many different connections are being uncovered. For example: during stress the body, which believes itself to be in imminent danger, uses cortisol to activate changes in the body to ensure that energy is available for a fight-or-flight situation, including suppressing the immune system, which uses a lot of energy. In a stressed person, cortisol levels are elevated for prolonged periods of time, leading to a weakened immune system. Of course, this mechanism evolved long ago, when you were more likely to run into a hungry predator than delays on the Central line. There is also evidence emerging that Oxytocin, produced during positive interpersonal interaction including hugging and mother-infant bonding, promotes significant health benefits such as the increased speed of wound healing.

Applicants for Medicine and Psychology should consider the links between these two fields, with reference to examples. They may wish to think about the role of serendipity and accidental discovery in research, as well as how developments in medical and scientific knowledge often depend on questioning preconceived ideas.

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