Psychoneuroimmunology
In 1975 Robert Ader and Nicholas Cohen advanced PNI with a demonstration of classic conditioning of the immune function, and coined the term "psychoneuroimmunology". Ader was investigating how long conditioned responses  might last in laboratory rats. The highly reproducible results showed that conditioned rats exposed to the conditioned stimulus were immuno suppressed. In other words, a signal via the nervous system (taste) was affecting immune function. This was one of the first scientific experiments that demonstrated that the nervous system can affect the immune system.