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AN EXAMINATION OF THE FUNCTIONAL RELATIONSHIP BETWEEN BRAIN AND LANGUAGE.

This paper focuses on the structure/function relationship of the brain and language. Specifically, this paper first reviews the basic theories concerning cortical structures and language representation. This review is followed by an examination of the major criticisms associated with each theory. Finally, a call for a more sophisticated analysis of the complex relationship between cortical and subcortial structures and language processing and production is presented. This call highlights the need to examine the areas of listening, memory, and information retrieval.

In the past years a number of Speech Communication scholars have turned to neurophysiological research to provide insight and clarity in to the way humans process linguistic stimuli. These speech-oriented studies have been vital in explaining the structure / function relationship of brain and language. However, now that the 'basic" introduction to the area of neurophysiology has been accomplished, it may be time to reevaluate the general principles we have adopted whole heartedly from early neurological studies. If an accurate assessment of language processes is to be achieved, a more sophisticated analysis of the intricacies of the brain, and that entity's role in the production of speech need to be considered. It is no longer appropriate to generalize about language functions and cortical structures. Language and Reading scholars should strive for specificity.

The purpose of this paper is three fold: first, a review of the basic theories related to cortical structures and language representation is presented. Second, the major criticisms associated with each theory are briefly outlined, and finally, some suggestions for adding increased specificity to future speech communication research concerned with cortical processing are offered.

The functional organization of the brain is an area of strong debate. The sensory and motor areas have been mapped (rather precisely), but the areas or structures associated with language processes are not quite as clearly known. What is it that permits an individual to possess language/speech? Why are humans the only creatures able to communicate via a grammatically governed symbol system? The nature and origin of the human capacity to encode and decode ideas into symbols has been an area afforded much scholarly attention. The interest in language comprehension, storage, and production, even after two hundred years of research, still hasn't given up its secrets. The basic issue in all attempts to solve the problem of the relation between language and brain is that of the cortical localization of language and speech: "Which part of the cortex are responsible for acquisition of language codes and their use?" (Luria, 1974, p. 1).

Broca and Wernicke were the first to provide hard -evidence concerning lateralization of speech/language functions in the brain. Carl Wernicke (1874) clearly illustrated a difference between aphasias produced by damage in the frontal lobe of the Left Hemisphere (LH) (i.e., Broca's area) and damage in the temporal lobe of the LH (i.e., Wernicke's area). Aphasia characteristic of Broca's are associated with expression disorders,- whereas, aphasia associated with Werrdcke's area are related to comprehension dysfunctions.

Wernicke illustrated that Broca's area is located in the internal portion of the left frontal lobe. This structure lies directly in front of the area of the brain responsible for the motor representation of the organs of speech (e.g., lips, tongue, plate, vocal cords and face). This discovery led to the assumption that Broca's area is the cerebral structure responsible for the mapping of language programs into articulatory form.

Wernicke's area is located adjacent to the cortical representation of hearing, and it is assumed that this area is involved in the recognition of the patterns of spoken language (Geschwind, 1970). These two areas (Broca's area & Wernicke's area) are believed to be connected by a nerve track This pathway permits the auditory form of a word to be transferred from Wernicke's area where a proposition, word, or idea is converted into a syntactic design to Broca's area where this design is programmed on to the muscles of articulation and projected to the organs of speech. Damage to either of these areas or the connecting neural tract would typically result in some form of aphasia.

Based on the discovery of these two cortical structures, the LH is believed to be the site of language localization. Localization is this sense means that a human function is accomplished within a specific structural location of the brain. Lateralization is characterized by the limiting of some function to one side of the brain or only one cerebral hemisphere. Evidence associated with the work of Broca and Wernicke led to the basic assumption that certain anatomical structures responsible for the reception and production of language/speech are located in the left cerebral hemisphere. However, there is not total agreement on this assumption

The most widely held theory of language-brain representation is "Cerebral Dominance." This theory argues that one hemisphere is dominant (i.e., LH and the other minor (i.e., RH) with regard to their association or contribution to language functions. One commonly held assumption is that there is a "direct relationship" between certain brain areas and language and speech functions. Functionally, the LH is believed to control the processing of linguistic material (Bogen & Gazzaniga, 1965, Broca, 1865, Kimura, 1961, Wernicke, 1874). Specifically, the LH is predisposed to process digitally or discretely patterned stimuli (e.g., words or numbers). In contrast, the RH controls the processing of non linguistic material (e.g., music, imagery, facial expressions). The mode of processing attributed to the RH is Gestalt or holistic organizations of continuous stimuli.

In connection with this dominant/minor hemispheric distinction, Lenneberg (1967) postulated a critical period hypothesis. In this theory Lenneberg asserts that a first language can only be learned between the ages of two and puberty. Before two years of age the brain is not mature enough to acquire language and after puberty the brain's neural network has lost the plasticity necessary for normal language acquisition and development. Plasticity, according to Lenneberg, refers to the neural synaptic flexibility which permits variant neural pathways over the cerebral cortex. After puberty this flexibility is lost. The neural pathways become "hard wired." The completion of neural synaptic connections associated with other non language abilities are no longer available. This hard wired condition results from insufficient linguistic stimulation of the language-related areas of the cortex. Theoretically, this lack of stimulation results in the functional atrophy of the LH or the loss of critical neural space necessary for speech/language processes to other nerve systems (e.g., sight, psycho-motor abilities).

Schneider (1976) has shown that developing nerve systems will compete for synaptic space. Also, nerves can compress so as to carry out normal neural functions in less cortical space. These two findings provide empirical support for the critical period hypothesis. Between 12 and 24 months of age, many areas of the brain contain a larger number of neurons than are needed to survive (Cowan, 1979). It is believed that those functions receiving primary stimulation exploit the large number of synapses available, resulting in an increased proficiency of those functions and limited space available to those less exercised functions. This competition for synaptic space continues until the abundance of synapse are eliminated from competitive interaction (Gardner, 1983). For example, nerve systems associated with physical movement or sense perception could control the cortical areas typically associated with speech/language functions, especially if the cortex has been deprived of sufficient linguistic stimulation to engender the growth of linguistic associated neural pathways.
 The normal feature of development also had adaptive advantages. If some
 damage occurs during a time when excessive connections are available, the
 chances are greater that the organism will survive despite injury. In
 support of this notion, a tremendous growth in cell connections occurs
 immediately after a lesion, sometimes as much as six weeks worth of growth
 occurring in seventy-two hours. Analogously, if one eye is removed at
 birth, the death of retinal gaglion cells, which would ordinarily occur in
 the first two postnatal weeks, is markedly reduced. (Gardner, 1983, p. 44)


This act of compression could explain right hemisphere language acquisition after early, extensive damage to the left hemisphere. The Critical Period hypothesis, at least in its weak form, has not been refuted. Therefore, it may be an accurate commentary on when language can be acquired. It does not, however, explain how language processing is accomplished.

In contrast with Lennenberg's theory, Geschwind (1972) offers a neuroanatomical model of language processing. Geschwind (1970) has developed a theory based on the analysis of information gathered from individuals suffering from various types of brain damage. This theory's basic argument rests on the belief that certain anatomical structures, responsible for the reception and production of language/ speech, are located in left cerebral hemisphere, and that this mutual structural/functional association, to some degree, is present at birth (Molfese, 1976). Physiological asymmetries were found associated with the cerebral representation of language -- the plannum temporal -- is larger in the left hemisphere than in the right hemisphere (Geschwind and Levitsky, 1968). Similar asymmetries were found in neonates (Witelson and Pallie, 1973) and fetuses (Wada, Clarke, and Hamm, 1975).

In Geschwind's model the grammatical and lexical representations of language arise in the superior temporal gyrus (Wernicke's area) of the LH, and these representations are transformed via a band of association fibers that course around the sylvian lip through the angular gyrus and into the frontal lobe, terminating in the third frontal convolution of the LH (Broca's Area). The band of association fibers responsible for the intra-hemispheric transfer of neural information is the arcuate fasciculus.

Geschwind's proposed theory appears logical. Wernicke's area is located adjacent to the area associated with the reception of auditory stimuli Heschle's gyrus, and Broca's area is located close to the cortical areas assigned to the motor control of the muscles of articulation. Considering Geschwind's theory in conjunction with the physical arrangement of the functional areas of the cortex, sound is received by Heschle's gyrus (1) this stimuli is monitored for linguistic patterns by Wernicke's area (2) and ideational symbols generated in Wernicke's area can be transferred forward to Broca's area (3) where these propositions are mapped onto the mechanisms of speech articulation.

The logic associated with Geschwind's theory is strong; however, empirical evidence tends to inhibit its total acceptance. There are records of lesions occurring in the arcuate fasciculus that have not resulted in aphasia. Because of the lack of speech disturbance even though a major link in the theory chain is severed leads one to question the accuracy of Geschwind's theory. There must be an alternate neural route connecting Broca's area and Wernicke's area (Brown, 1975).

Brown (1975) suggests that the thalamaus is related to cortical functions associated with speech/language. He also argues against naive functional organizations associated with cortical lateralization. Brown and Jaffee (1974) assert that lateralization is not a state, but a developmental process. The lateralization process develops from inter-to intra-hemispheric localization. According to their conceptualization, the pulvinar is believed to be the primary mediator of language functions.

Anatomically, there are strong fiber connections between the pulvinar and the temporo-parieto cortex. Because of these physiological structures, and because children of different ages evidence different aphasic symptoms resulting from damage to different cortical locations, Brown further posits a four stage model of neocortical evolution.

Auditory stimuli do not enter directly into the new-cortex. In an abbreviated explanation, sound vibrations begin their journey to the cortex in the cochlea of the inner ear. From there the stimuli are transmitted along the auditory nerve to the brain stem from which fibers radiate out into Heschle's gyrus and then on to Wernicke's area. Accordingly, speech does not enter the cortex directly, but must first travel through the subcortical bodies including the thalamus.

Criticism of Theories

One of the major problems with the theories reviewed is their restricted view of language processes. Even Brown and his evolutionary development of language lateralization appears to be underestimating the complexity of language by focusing primarily on the articulatory aspects of speech or the superficial aspects of speech/reading comprehension.

For the purposes of theory building, it would seem beneficial to examine the epistemological potential of each of the following areas:

(1) Input Processes- The process of decoding LANGUAGE from linguistic stimuli. Here full range neurological mapping of the listening and psycho-acoustic networks would prove invaluable in coming to understand how linguistic stimuli are transformed into symbols that are comprehensible.

(2) Central Processes- The organizational dimensions of verbal (semantic) memory and verbal (semantic) thought. How does the mind index, date, store, and retrieve data? How does the mind maximize heuristics? Or, as Ogden and Richards (1923) wondered half a century ago, how does language mean? Perhaps it is more than an associative process. For too long the emphasis has been on understanding the functions of the software without having the tools to understand the hardware that makes it work. Now that neurological technologies are breaking neural codes that have long mystified neurologists, the time is right for crossdisciplinary cooperation to address the question, "How does meaning mean?"

(3) Output Processes- The process of extracting verbal thought from memory traces, and the encoding of these thoughts into a linguistic pattern that will be articulated. There are essentially three scholastic camps in output processes: the cognitive camp, which focuses on memory, the linguistic camp, which is concerned with the process of information retrieval; and the social camp, that focuses on that which is socially appropriate as a guide to understanding linguistic output. It is clear, however, that these different perspectives do not function independent of each other. Efforts must be made to describe and explain the integration of these perspectives and the role each play in the production of complex communication.

In addition to these three processes, the modality employed to encode/decode symbolic content must also be considered. Does linguistic stimulation occur via auditory or visual means and does the individual processing this input respond orally or in written form. Developing a model of cortical representation of speech/language without considering these elements is to consider only part of the entire picture.

In summary, humans appear to have certain functional capabilities localized predominantly to the left hemisphere which provide them with the ability to decode and encode linguistic stimuli. The structural location of these functions are generally assumed to be the third frontal convolution of the LH (i.e., Broca's area), the superior temporal gyms of the LH (i.e., Wernicke's area). The supramarginal gyms and the angular gyrus, located in the posterior portion of the LH, are assumed to be responsible for the ability to read. And the supplemental motor speech area (Penfield & Roberts, 1957), found anterior to the pre-motor strip of the LH, is typically associated with automatic speech, for example overlearned linguistic patterns such as vulgarity, pledges, or prayers.

The connection between these areas of the left hemisphere and the specific role the right hemisphere in linguistic processes is not well established. It is known, however, that the right hemisphere is more efficient at processing nonverbal, spatial stimuli than the LH (Anderson, et al., 1975; Jaffee, 1978). However, just how much the RH aids the LH in comprehending and producing linguistic information is not yet known. To assume that the RH has little or no responsibility in processing linguistic material, or to consider only the activities of the cortex of the LH when analyzing linguistic processing is to limit one's analysis to only a small portion of the process. In order to fully understand language/speech processing, cortical as well as subcortical structures must be examined. Furthermore, the type of processing required (ie., decoding, organizing, encoding) and the modality used to initiate stimulation must also be included in the research model.

References

Andersen, P.A., Garrison, J.P., & Andersen, J.F. (1979). Implications of a ncurophysiological approach for the study of nonverbal communication. Human Communication Research, 6 (1), 74-89.

Bogen, J.E. & Gazzaniga, M.S. (1965). Cerebral commissurotomy in man: Minor hemisphere dominance for certain visuospatial functions. Journal of Neurosurgery. 23,394-399.

Broca, P. (1861). Nouvelle observatin d'aphemie produite par une lesion de la moire posterieure des deuxieme ct troisicme circonvolutions frontales. Bulletin de la Society Anatomique de Paris. 36 398-407.

Brown, J.W. (1978). Lateralization: A brain model. Brain and Language. 5,258-261.

Cowan, W.M. (1979). The development of the brain. Scientific America, 241, 112-133.

Gardner, H. (1983). Frames of Mind. New York- Basic Books, Inc., Publisher.

Geschwind, N., & Levitsky, W. (1968). Human brain: Left-right asymmetries in temporal speech regions. Science, 161, 186-187.

Jaffee, J. (1978). Parliamentary procedure and the brain. In A.W. Siegman & S. Feldstein (Eds.), Nonverbal Behavior and Communication. Hillsdale, New Jersey: Lawrence Erlbaum Associates.

Kimura, D. (1961). Some effects of temporal-lobe damage on auditory perception. Canadian Joumal of Psychology, 15, 156-165.

Lenneberg, E.H. (1967). Biological Foundations of Language. New York: John Wiley and Sons, Inc.

Luria, A.R. (1974). Towards the basic problems of neuro linguistics. Brain and Language, 1, 1-14.

Molfese, D.L. (1976). Auditory evoked potentials in left and right hemispheres of infants. Paper presented at the Fourth Annual Meeting of the International Neuropsychology Society, Toronto, February.

Ogden, C. K. & Richards, 1. A. (1923). The Meaning of Meaning. N.Y.: Harcourt Brace Jovanovich.

Penfield, W. & Roberts, L. (1959). Speech and Brain Mechanisms, N.J.: Princeton University Press.

Schneider, G-E. (1978). Growth of abnormal neural connections following focal brain lesions: constraining factors and functional effects, in W.H Sweet, S. Obrader, and J.G. Martin

Rodreguez (Eds.). Neurosurgical Treatment in Psychiatry. Baltimore: University Park Press.

Wada, J.A., Clarke, R., & Hamm, A. (1975). Cerebral hemispheric asymmetry in humans. Archives of Neurology. 14, 221-222.

Wernicke, C. (1874). Der aphasische symptomencomplex. Eine psychologische studie auf anatomischer basis, Breslau: Cohen & Weigert.

Witelson, S.E & Pallie, (1973). Left hemisphere specialization for language in the new bom: Neuroanatomical evidence of asymmetry. Brain. 96 641-646.

JEFFREY S. McQUILLEN Assistant Professor Communications Department

University of Texas - Pan American Edinburg, TX 78539

WILLIAM F. STRONG Associate Professor Communications Department University of Texas - Pan American Edinburg, TX 78539
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Author:MCQUILLEN, JEFFREY S.; STRONG, WILLIAM F.
Publication:Reading Improvement
Geographic Code:1USA
Date:Mar 22, 2000
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