Publisher Summary

This chapter presents an introduction to speech-language neurology. The brain is the source of all speech and language behavior. Hence, current knowledge concerning its anatomy and functioning must be studied and absorbed by a speech-language pathologist. But it is not the responsibility of the clinical speech-language pathologist to diagnose a neurologic disorder. This function is in the realm of the physician. Nevertheless, it is the responsibility of the speech-language pathologist to assess all relevant aspects of speech and language in those with a known or suspected neurologic disorder. The study of the relationship between the brain and speech and language function has a rich history in the past hundred twenty-five years, and the disciplines of speech-language pathology and neurology have often cooperated in the study of neurologically based communication disorders. Employing both verbal reasoning (left-hemisphere function) and visual imagery (right-hemisphere function) contributes to a successful experience.

“We must admit that the divine banquet of the brain was, and still is, a feast with dishes that remain elusive in their blending, and with sauces whose ingredients are even now a secret.”

—MacDonald Critchley, The Divine Banquet of the Brain, 1979

Why Neurology?

Every student of communicative disorders realizes without being taught that the brain is the source of all speech and language behavior. Nevertheless, many students shy away from achieving a basic understanding of the neural mechanisms of speech, language, and hearing because they believe the nervous system is overwhelmingly complex and abstruse. This complexity and obscurity, they fear, will lead only to perplexity and frustration if they attempt serious study of neuroanatomy and neurophysiology.

To compound this attitude, many academic training programs in communicative disorders treat the neurologic aspects of their discipline only superficially, arguing that this aspect of our knowledge is more properly the domain of medicine. In fact, some training programs in communicative disorders would make neurology the exclusive domain of the physician. The arguments generally cited for this point of view are, first, that neurology has little relevance to diagnosis or the day-to-day clinical management of the communicatively disordered client, and, second, that operant/behavioral management principles have been demonstrated to be effective in improving the speech and language of clients. These principles assume no neurologic explanation. This general position is expressed by Starkweather (1983).

Effective as behavioral principles have been in the diagnosis and management of communicative disorders, elevation of operant techniques to a central position in both the theory and practice of speech and language pathology may force the speech-language pathologist into the role of a mere technician, expert at dealing with only one facet of a multifaceted problem. This limited view will never permit a complete understanding of the disorders of speech and language.

There has been an increasing interest in the neurologic aspects of speech and language pathology in the past two decades. Language development and its disorders are being studied in the context of developmental neurology and biological explanation (Lenneberg, 1967). A clearer understanding of the motor disorders of speech has been gained in the last two decades, and the literature on dysarthria and apraxia of speech has been expanded impressively. Interest in the study and treatment of aphasia has so increased that there is now a subspeciality called clinical aphasiology. Research and writing on cerebral speech and language disorders and their mechanisms are no longer solely the province of neurologists, as was almost always the case in the past. Today, the speech-language pathologist, the neuropsychologist, and the neurolinguist are major contributors to the ever-growing abundance of literature on neurologic communication disorders.

In a significant manner this literature reflects the fact that the modern-day speech-language pathologist is playing an expanded and crucial role in the rehabilitation of persons with neurologic disorders. Since World War II, the speech pathology service has become an accepted service in the standard rehabilitation center and many general hospitals. As the role of the speech-language pathologist expands in the rehabilitation of the neurologic patient, the neurologic information and background expected to be part of the academic training will be considerably larger in scope. Future speech-language pathologists will view themselves as important students and contributors to the field of neuroscience. Speech pathology will be one of several specialties contributing to the discipline of behavioral neurology.

It should be emphasized that it is not the responsibility of the clinical speech-language pathologist to diagnose a neurologic disorder. This function is in the realm of the physician. Nevertheless, it is the undeniable responsibility of the speech-language pathologist to assess all relevant aspects of speech and language in those with a known or suspected neurologic disorder. The speech-language pathologist must be accountable for understanding the results of this speech-language assessment in terms of the underlying neurological mechanisms. Further, the clinical speech-language pathologist must be conversant with current methods of neurologic diagnoses and treatment as they apply to persons with communicative disorders. The neurologist’s point of view toward speech and language disorders should be familiar to every clinician. In turn, the neurologist must be conversant with assessment methods and therapy procedures of the communication disorders specialist. This is particularly crucial now, since both disciplines have developed relatively independently in the past half century, sometimes to the detriment of both professions and the people they serve.

Historical Roots: Development of a Brain Science of Speech-Language

Speech-language pathology has many of its roots in neurology. In 1861 the French physician, Pierre Paul Broca (1824–1880), studied the brains of two patients who both sustained a language loss and a motor speech disorder. This allowed him to localize the human speech center to a definite circumscribed area of the left hemisphere, and a brain science of speech and language was irrevocably established. Broca’s discovery went far beyond the now classic description of an interesting brain disorder called aphasia. Possibly foremost among his conclusions was the assertion that the two hemispheres of the brain were asymmetrical in function and that the left cerebral hemisphere contained the speech center in the majority of the population. Important implications of asymmetry of the brain are even now coming to light in neuroscience research some thirteen decades later. Asymmetry of function is more pervasive than was thought earlier. It extends well beyond speech to other brain areas and their functions.

Another conclusion that has had everlasting importance for neurology since Broca’s death is that specific behavioral functions appear to be associated with clearly localized sites in the brain. The collorary of this observation is that behavioral dysfunction can point to lesions at specific sites in the nervous system. The concept of localization of function in the nervous system has been demonstrated repeatedly by clinical and research methods since Broca first articulated it over a century ago. This observation was so profound that it became a significant historical force in the establishment of the medical discipline of clinical neurology. Much of clinical neurology is dependent on the physician’s ability to lateralize and localize a lesion in the nervous system.

Very important for speech-language pathology was the fact that Broca’s discovery stimulated a period of intensive search for a workable explanation of the brain mechanisms of speech and language. Probably no period in the history of neurologic science has so advanced the understanding of communication and its disorders as those years between the date of Broca’s discovery and World War I.

One of the first and foremost outcomes of this intensive study of speech-language brain mechanisms was the establishment of neurologic substrata for modalities of language deficit other than the expressive oral language described by Broca. In 1867 William Ogle published a case that demonstrated that a cerebral writing center was independent of Broca’s center for speech. Carl Wernicke (1848–1905) in 1874 identified an auditory speech center in the temporal lobe; it was associated with comprehension of speech as opposed to Broca’s area in the frontal lobe, which was an expressive speech center. Lesions in Broca’s area produced a motor aphasia, in Wernicke’s area a sensory aphasia. In 1892 Joseph Dejerine identified mechanisms underlying reading disorders. Disorders of cortical sensory recognition, or the agnosias, were named by Sigmund Freud in 1891, and in 1900 Hugo Liepmann comprehensively analyzed the apraxias—disorders of executing motor acts resulting from brain lesion.