Convinced that mental functions are localized in specific regions of the brain and that human behaviour is dependent upon these functions, Gall assumed that the surface of the skull faithfully reflects the relative development of the various regions of the brain. His popular lectures in Vienna on “cranioscopy” (called phrenology by his followers) offended religious leaders, were condemned in 1802 by the Austrian government as contrary to religion, and were banned. Three years later he was forced to leave the country.

His concept of localized functions in the brain was proved correct when the French surgeon Paul Broca demonstrated the existence of a speech centre in the brain (1861). It was also shown, however, that, since skull thickness varies, the surface of the skull does not reflect the topography of the brain, invalidating the basic premise of phrenology. Gall was the first to identify the gray matter of the brain with active tissue (neurons) and the white matter with conducting tissue (ganglia).