This book demonstrates for the first time the connection between age, disease in old age, psychiatric disorders, pain, psychosomatic phenomena on the one hand and the function of neurotransmitters on the other and attempts to explain the significance of these substances for our behaviour. The authors therefore offer a biological approach to psychotherapy, drug dependence, neurosis and psychopathy, which have hitherto been seen from a purely psychiatric angle. This modern version of the hypothesis that "the balance of neurotransmitters is a condition for normal behaviour" will surely give an impulse to further far-reaching research.