The stress response of the body involves all body systems. The heart and blood vessels, the immune system, the lungs, the digestive system, the sensory organs, and brain are modified to meet the perceived danger.
External stressors include adverse physical conditions or stressful psychological environments.
Internal stressors can also be physical or psychological. An example of an internal psychological stressor is intense worry about a harmful event that may or may not occur.
Accurately calibrated music synthesis software has been used to create the exact isochronic beat frequencies required to induce a deep relaxation of mind and body.
Experimenting through the whole range of alpha waves (from 8 - 12 Hz) it was found that a combination of frequencies consistently caused a spontaneous relaxation of mind and body.