Though there have been various psychological accounts of aphasia over the years, only one -- Wernicke's -- anatomical theory has ever been proposed. According to this theory, speech perception occurs over a series of stages in the posterior-superior temporal region ( Wernicke's area), which both transmits to (for repetition) and modulates Broca's area. Language produced in the posterior brain is conveyed by an uncertain path to Broca's area for articulation. In more modern accounts, mechanisms are assumed to be located within the anterior and posterior regions, which can account for the diversity of clinical symptomatology: for example, mechanisms for sound, word, and meaning perception; for discrimination and sequencing; for various short-term memory and long-term memory processes; a parietal dictionary attached to Wernicke's area accounting for anomia; impaired verbal or auditory feedback. Luria's classification is derived from Wernicke's approach, since similar mechanisms are inferred ad hoc from the clinical picture. In such theories, every new observation implies a new mechanism and results in a chaotic patchwork of areas, mechanisms, and interconnecting paths.
The anatomical model of aphasia presented in this chapter differs fundamentally from this classical account. Limbic and neocortical zones identified with aphasic disturbances are viewed as strata or levels in the evolutionary and maturational structure of the brain. In this model, there is no rostral conveyance of language content, but rather a simultaneous realization of the entire hierarchical system within its anterior and posterior sectors. Nor are there separate processes or strategies operating on language content; instead, there is a resubmission of emerging abstract content at each hierarchical level to the same reiterated process -- in other words, one process at multiple levels, rather than multiple processes at the same level. These differences from the traditional approach will become more apparent as we proceed into the actual model.____________________