Chemical bases of behavior.

Abstract

Efforts to relate behavior to chemical substances and events in the brain date from ancient Greek physiology and medicine. Hippocrates speculated that the human body consists chemically of four humors: bile, black bile, phlegm, and blood. Temperamental differences between persons were supposed to reflect differences in the proportions of these humors. The adjectives in our own language which correspond to Hippocrates' four basic temperaments still reveal the influence of these humoral notions. They are choleric, melancholic, phlegmatic, and sanguine.Significant progress in understanding the chemical bases of behavior has been a very recent development. Progress had to await the development of adequate technics for measuring behavioral changes which accompany chemical changes in the brain. Also, there are special problems involved in experimentally manipulating the chemical composition of the brain. The brain as a whole has a remarkable tendency to maintain its chemical constancy (homeostasis). This is due in part to a functional barrier between the blood and the brain tissue which prevents all but a few chemicals from entering the brain proper. The anatomic location of this blood-brain barrier is a matter of dispute but most authorities place it at the capillary wall or glial mantle. The barrier appears to function to protect the brain against the myriad chemical fluctuations reflected in the blood.