There are three major theories on how the brain is organized, in terms of its structure and function. Phrenology was proposed by Gall in the late 18th century who thought it was possible to determine character traits by examining the external bumps on the head. All behavior/mental function was assigned a location in the brain, and using more or less of these regions determined these bumps. The aggregate field view was raised by Flourens (1920s) using experimental evidence that showed that all areas are important for each mental function. So any part can perform all functions and there was no localization. Cellular connectionism (supported by Hughlings Jackson, Wernicke, Sherrington, Ramon y Cajal) states that individual neurons are signalling units that are arranged in groups, each having a particular function. References E. R. Kandel, J. H. Schwartz, T. Jessell, Principles of Neural Science (McGraw-Hill, New York, ed. 4, 2000).