Introduction

The regular recurrence of aphasic syndromes, especially with strokes, has formed the basis of the cortical localizationist models and has provided clinicians a solid foundation for diagnosis and prognosis. Approximately 25% of stroke patients have significant aphasia (Leske, 1981), making this a common neurological and rehabilitation issue. Broca (1861) established the importance of the left hemisphere in language. Meynert (1867/1868) is credited with the motor sensory dichotomy of cortical function and also with recognizing the accompanying anteroposterior anatomical distinction. Wernicke (1874), subsequently, extended the description of aphasic syndromes including comprehension deficit, on the basis of this motor–sensory dichotomy. Upon these foundations, a number of aphasic syndromes have been described subsequently. The taxonomy of these syndromes has been much debated, but in Table 15.1 the most commonly accepted classification and terminology are summarized. The issue of specialized language cortex, functionally unique and anatomically localizable, similar to the primary motor or visual cortex, has become an important question for research. The existence of such a language cortex is supported by the large number of persisting aphasic patients and the anatomical and physiological evidence for networks for language output and comprehension. The characteristics of such networks can be summarized as: (i) a function is represented at multiple sites, therefore lesions from multiple sites can produce a similar deficit, (ii) each area may belong to several overlapping networks, therefore a lesion in a single area often produces multiple deficits, and (iii) severe and lasting deficit of function occurs when all or most structural components of a network are involved.