Historical trends in biological and medical investigations of reading disabilities: 1850-1915.

The theoretical roots of neuropsychological research lie in the case studies of reading disability completed during the late nineteenth and early twentieth centuries. This article reviews the methods, technologies, and operating tenets of these studies. The results suggest that the assumptions of anatomical and functional modularity for cortical processes became guiding principles for diagnosing and correcting reading difficulties. The advent of neuron doctrine shifted the focus of neuropsychological explanations of reading difficulties from gross neuroanatomical studies to investigations of the microstructure of the central nervous system. Early definitions of reading disabilities are interpreted across the dimensions of focal lesions, autonomous cognitive processes, comorbidity with other symptoms and syndromes, etiology, and permanence.