Redefining Wernicke's Area: Receptive Language and Discourse Semantics

Journal of Allied Health, Summer 2007 by Tanner, Dennis C

This report calls for a more exacting definition of Wernicke's area in the discipline of communication sciences and disorders to reflect an accurate view of brain functioning with regard to decoding discourse semantics. Conventional definitions are provided to delineate the general usages of important terms used by many professional dictionaries and glossaries when defining Wernicke's area, receptive aphasia, understanding, and comprehension. Five levels of semantic decoding are described. A stanza from Tennyson's In Memoriam is used to show the dynamics of discourse semantic decoding and to logically establish that "language understanding" can virtually engage the brain as a whole and the totality of a person's mind. A more accurate definition is provided, indicating that Wernicke's area is not the center for oral language understanding, only an important conduit to language comprehension. J Allied Health 2007; 36:63-66.

IN 1874, a young German neurologist, Karl Wernicke, identified the sensory or receptive area of communication in the left hemisphere of the brain, particularly the temporal lobe, in his book entitled Der Aphasische Symptamenkampleks. Zemlin1 showed Wernicke's area to also extend into the parietal lobe. Wernicke's area, the so-called "receptive language center" of the left hemisphere, is usually described as consisting of Brodmann sites 22, 41, and 42,2 although some authorities list the sites comprising Wernicke's area as Brodmann sites 22, 39, and 40 (Figure 1). Wernicke noted that a patient with sensory aphasia has impaired understanding of speech not attributable to hearing loss or deafness and may produce jargon.

Traditional thought in communication sciences and disorders attributes Wernicke's area as the site in the brain where language is recognized, perceived, interpreted, and understood. Whereas Broca's area (primarily Brodmann site 44) is the presumed site for language "expression," Wernicke's area is the contrasting site where spoken language is "understood." While Wernicke's area may be an important conduit for decoding perceptual, phonological, grammatical, and semantic features of language, attributing this site as the center for oral language understanding is based on inexact and narrow definitions of the words.

Attempts to localize receptive language to one or more brain sites of a hemisphere or lobe of the brain, perhaps more than any other attempts to localize a human cognitive function, are fraught with possibly insurmountable obstacles. Although language localization movement is a widespread practice in the speech and hearing sciences, the biggest localization flaw lies with the vague definitions of what function is localized.

The practice of defining Wernicke's area as the center for understanding can be traced to early writings in speech pathology and audiology. Wood3 defined Wernicke's area as "a region in the superior convolution of the temporal lobe of the cerebrum identified as the center for understanding speech heard" in Lee Edward Travis' classic textbook entitled Handbook Speech Pathology and Audiology. Davis4 noted, "The interpretation of auditory language input in the left hemisphere is handled posteriorly to Heschl's gyrus in a region called Wernicke's area." Stedman's Concise Medical Dictionary for the Health Professions (4th edition) defined Wernicke's area as "The region of the cerebral cortex thought to be essential for understanding and formulating coherent, prepositional speech. . . ."5 In Terminology of Communication Disorders: Speech-Language-Hearing (5th edition), Nicolosi et al6 defined Wernicke's area as the "region in the superior convolution of the temporal lobe of the cerebrum which is identified as the center for understanding oral language; corresponds approximately to Brodmann areas 22, 39, and 40." Regardless of the fact that many neuroscientists recognize the limited receptive language functions of Wernicke's area, dictionaries and glossaries in communication sciences and disorders continue to attribute it as the center for language understanding.

Most dictionaries define "understand" as the perception of the meaning of words, appreciation of the significance of a statement, interpreting the implications of an idea, and inferences that can be drawn from a statement.7 Webster's New World College Dictionary8 makes the distinction that while "understand" and "comprehend" are used interchangeably, "understand" stresses the full awareness or knowledge arrived at. The word "center" is typically used synonymously with concentrated, primary, and core and is Greek for kentron or "sharp point."

The primary auditory cortex, also known as Brodmann area 41, is located in the parietal-temporal area of the cortex. The secondary auditory cortex, Brodmann area 42, and the auditory association cortex, Brodmann area 22, are essential cortical regions for auditory reception and association. However, there is bilateral hemispheric auditory representation and both hemispheres of the brain receive auditory input. Nevertheless, there is typically a right ear advantage in most people, showing that despite the bilaterality of ascending auditory pathways, the contracterai pathways are still predominant and the right ear is represented more abundantly in the left hemisphere.9 As noted by Martin and Clark, "At one time it was believed that the auditory cortex was the only center of auditory discrimination. It is now known that many discriminations may be mediated subcortically."10