The perversion of language: Jules Baillarger on aphasia, the lateralization of speech, and the Baillarger-Jackson principle.

Jules Baillarger was one of the foremost figures of nineteenth-century neurobiology. He is remembered today for his discovery that the human cerebral cortex is composed of six intercalated layers. Even today, two horizontal fiber bundles within cortical layers IV and V are referred to as the outer and inner bands of Baillarger. It is a measure of the importance of Baillarger's discovery that his findings were elaborated upon with advances in microscopy and the development of methods for staining neurons and myelin by, notably, Theodor Meynert and Santiago Ramon y Cajal. Furthermore, Baillarger's observation that there are variations in the thickness of one or another of the six cortical layers in different cortical regions, and the discovery of giant pyramidal motor neurons in layer V of the precentral gyrus, ultimately led to the architectonic and architectonic maps of Oscar Vogt and Cécile Vogt-Mugnier, and of their student Korbinian Brodmann (1908). Less well known are Baillarger's contributions to the semiology of aphasia and the pivotal role he played in the recognition of the localization and lateralization of speech to the left hemisphere. Paul Broca's localization of articulate language to the posterior aspect of the frontal lobes and Marc Dax's discovery that speech is a function of the left hemisphere were vigorously challenged within French academic medicine until 1865, when Baillarger gave two addresses to the Royal Academy of Medicine. In the first address, he described a form of aphasia he called the , which we now call fluent aphasia, and reported that aphasic patients can express words or parts of sentences when they are angry or excited, a phenomenon now known as the Baillarger-Jackson principle. In his second address, Baillarger supported the lateralization of speech to the left hemisphere of the brain and referred to this association as Dax's "singular law," and supported the localization of speech to the posterior aspect of the left inferior frontal gyrus. Baillarger's description of the perversion of language and of the influence of emotions on speech presaged the discipline of aphasiology, and his support for the lateralization of speech to the left hemisphere marks the first instance of the unequivocal recognition of asymmetrical hemispheric functions by academic medicine. This article reviews these aspects of Baillargher's career. Critical sections of his papers on cortical structure, aphasia, and functional hemispheric asymmetry are translated by the author.