Illustrating a revolution: an unrecognized contribution to the golden era of cerebral localization.

The late 19th century witnessed a remarkable growth of knowledge concerning the functions of the brain. The excitability of the cerebral cortex was first reported by Gustav Fritsch (1838-1927) and Eduard Hitzig (1838-1907) in 1870, followed by the classical investigation of cerebral localization by David Ferrier (1843-1928). Ferrier's identification of cerebral motor centres based on a series of cortical stimulations and ablations was central to the physiological and clinical achievements of cerebral localization in the late 19th century. Cerebral illustrations were an important component of Ferrier's physiological research, synthesizing a great deal of experimental data and suggesting precise locations and boundaries of sensory and motor areas. Surprisingly, little attention has been paid to the construction of cerebral maps and their role in establishing the utility and veracity of the doctrine of cerebral localization. Two illustrations of the macaque brain based on Ferrier's experimental work were particularly influential. These and other important illustration accompanied Ferrier's manuscript, "the localisation of functions in the brain", submitted to the Royal Society in early 1874, but were not produced by Ferrier himself. Rather, they were sketched by E.A. Waterlow (1850-1919), a young painter and acquaintance of Ferrier's who--undoubtedly under Ferrier's guidance--synthesized the experimental data of more than a dozen experiments in these diagrams. Unfortunately, during contentious review, abstraction and fragmentation of Ferrier's manuscript, Waterlow's monogrammed insignia was omitted from reproductions of his sketches and Ferrier's acknowledgement to him was not published in subsequent works.