Brown-Séquard and cerebral localization as illustrated by his ideas on aphasia

Brown-Séquard's concept of localization was built on the phenomena of inhibition and dynamogenesis, constituting a dynamic system in which reflex mechanisms, that played a part not only in the spinal cord but in the brain as well, were considered of particular importance. The use of this concept is considered in Brown-Séquard's discussion of the subject of cerebral localization, and especially of aphasia. The origin and development of Brown-Séquard's ideas on aphasia from 1861 onwards are discussed, as is the part he possibly played in the transfer of knowledge from Paris to London (Broca and Jackson). In the 1870's Brown-Séquard debated on cerebral localization with Charcot before the Société de Biologie. Opposing the cluster theory of localization, Brown-Séquard developed the theory of "réseau de cellules anastomosées", a kind of network theory in which scattered cells subserving the same function are connected by nerve fibers. This was to him a plausible theory, with which he was able to explain the fact that damage in several locations may produce the same effect, and, to account for observations that some functions remain unimpaired despite extensive brain-injury. Although Brown-Séquard's arguments were not always valid, because they were based on imprecise observations, his dynamic model, nowadays, seems valuable. He influenced "anti-localizers" such as Goltz, but also Jackson and probably Von Monakow and Sherrington.