An advanced field of research that studies the complex interactions of the nervous, immune and endocrine (hormonal) systems, as well as their impact on each other and on human health. This area explains, for example, how chronic stress can lead to the release of hormones such as cortisol that weaken the immune system, or how immune changes can affect mood and behavior. It also shows that the body and mind function in a complex network of chemical, neurological, and hormonal signals, meaning that any imbalance in any of them can lead to physical or psychological disorders. This area of research is fundamental to understanding psychosomatic illnesses and developing holistic therapeutic interventions that integrate biological and psychological aspects.