Mapping Behavior to Lesion Location in Neurolinguistics: History and The Illusive Methodology

At first glance it seems as though the history of aphasia, a neurological deficit in language, is teaming with thorough, well characterized research using lesions to determine the language centers of the brain. A brain lesion is classified as tissue in the brain that is damaged due to disease or injury. The location of these lesions is a fundamental part of understanding how the structures of the brain affect the way humans think and behave; lesion mapping is the process used by researchers to identify this relationship. Exploring the history of this process reveals an epidemic of poorly described methodologies. Iconic names in aphasic study including Carl Wernicke, Ludwig Lichtheim, and Henry Head, credited with major aphasic discoveries, produced literature with a markedly limited, sometimes nonexistent descriptions of methodology. Thanks to the work of Broca, Dejerne, Montier and a few almost unheard-of anatomists, we retain some small insight into the development of lesion localization methodology. Still, there has been a consistent prioritization of the clinical pathology of these disorders over autopsy and detailed lesion topography, a practice which continued into the technological age neurological imaging. Today, as the complexity of these methods increases, details of the most up-to-date lesion mapping methods can still only be found by compiling the methods sections of lesion-based localization studies. This project emphasizes the need for literature dedicated to methodology and the fundamental principles of quality research standards to create more effective functional understanding of the human brain.