Russell J. Love

Language performance on visual processing tasks in right hemisphere lesion cases

Abstract Seven language tests were constructed or adapted to assess the performance of three groups of 10 right-handed adult subjects: a right hemisphere lesion (RHL) group, a left hemisphere lesion (LHL) group, and a neurologically normal (NN) control group. Both the LHL and RHL groups produced poorer scores than the NN group on six of the seven tests. On two of the six significant tests, the RHL performed more poorly than the NN group. Analyses of words uttered during an oral story telling test indicated that the RHL group told significantly fewer complete stories using significantly more nouns, adjectives, and conjunctions than the NN group. On a 7-point scale, three judges rated the overall communication abilities of the RHL group as having “mild problems,” a significantly different rating than the ratings of the LHL and NN groups. The findings suggest that underlying visual spatial and perceptual deficits may be accompanied by clearly recognizable language differences in certain subjects.

The Cranial Nerves

Publisher Summary This chapter highlights the parts of the nervous system involved in the act of speaking. The cranial nerves make up a part of the peripheral nervous system that provides crucial sensory and motor information to the oral musculature. The cranial nerves are vital for speech production, and the speech-language pathologist must be knowledgeable about their functions. There are 12 pairs of cranial nerves and 6 of them are directly related to speech production—cranial nerves V (trigeminal), VII (facial), VIII (acoustic-vestibular), IX (glossopharyngeal), X (vagus), and XII (hypoglossal). This chapter refers to the embryologic origin of the cranial nerves, explaining those which are somatic or branchial in origin and those which are solely special sensory nerves. The chapter also discusses the anatomy, innervation, function, and testing of each of the nerves associated with speech. It describes the cooperation of several cranial nerves in the act of swallowing.

1 – Introduction to Speech-Language Neurology

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.

Neurosensory Organization of Speech and Hearing

This chapter discusses the neurosensory organization of speech and hearing. Three major pathways carry sensory impulses from the extremities and trunk to higher levels of the nervous system. One of these is the spinothalamic tract that has two divisions—the lateral spinothalamic tract and the ventral spinothalamic tract. The lateral spinothalamic tract conveys impulses of pain and temperature. The ventral spinothalamic tract conveys impulses of light touch, light pressure, and tactile discrimination. The second major pathway is known as the dorsal column. The two tracts of the dorsal column are the fasciculus gracilus and the fasciculus cuneatus. The third major pathway includes the spinocerebellar tracts. The dorsal pathway ascends contralaterally. Both pathways end in the cerebellum and are thought to mediate conscious proprioception of movement. Cerebral lesions, marked by language loss, may have accompanying sensory loss involving the parietal lobe or subcortical pathway. The oral cavity is very rich in sensory receptors. Tactile receptors of the mouth, tongue, pharynx, and teeth play a significant role in the articulation of speech.

The Neuromotor Control of Speech

This chapter discusses the neuromotor control of speech. The neuromuscular control for speaking occurs in three classic motor systems: (1) the pyramidal, (2) extrapyramidal, and (3) cerebellar systems. When the corticospinal tract of the pyramidal tract is damaged by an upper motor neuron lesion, a contralateral hemiplegia (one-sided paralysis) may result. The corticobulbar tracts are the voluntary motor pathways for speech; they are part of the pyramidal system. Corticobulbar fibers innervate the cranial nuclei in the pons and medulla for the cranial nerves that control speech. The crossed and uncrossed fibers of the corticobulbar tracts are arranged so that the midline speech muscles function in bilateral synchrony for many functions. Some speech muscles show mixed bilateral synchrony and contralateral independence. The cerebellum is responsible for synergistic motor coordination and plays an important part in guiding the rapid, alternating, repetitive movements of speech. It provides afferent and efferent information to the corticobulbar fibers.

Language Mechanisms in the Developing Brain

This chapter discusses the language mechanisms in the developing brain. Acquisition of speech and language is clearly tied to physical development and maturation in the infant and child. Two indices of brain growth—changes in brain weight with advancing age and the differential myelination of cerebral structures—appear to be valid correlates of speech and language development. Neuroanatomic differences, such as larger left temporal planums and longer sylvian fissures on the left, found in the majority of fetuses and infants, provide some support for an early lateralization of language mechanisms. Infants who sustain damage to the left hemisphere before 1 year of age demonstrate a degree of early cerebral plasticity for language mechanisms. Developmental language disability without evidence of focal brain lesions has long been associated with the primary etiologies of deafness, mental retardation, and childhood autism. Many children with language delay and disabilities present unknown etiologies but are suspected of cerebral dysfunction. Signs of minimal cerebral dysfunction cannot always be established on neurologic examination, and an idiopathic neurologic disorder is suspected.

Clinical Speech Syndromes and the Developing Brain

This chapter discusses the clinical speech syndromes. The developmental motor speech disorders include developmental dysarthria, developmental anarthria, and developmental apraxia of speech. Developmental dysarthria is by far the most common of the motor speech disorders and is most frequently seen in children with cerebral palsy. Cerebral palsy is primarily a movement disorder caused by damage to the immature brain. The three major clinical syndromes of cerebral palsy are spasticity, athetosis, and ataxia. Most cerebral palsied children present multiple disabilities in addition to their motor disorder. Next to cerebral palsy, childhood muscular dystrophy is the most common motor disorder in children. Pseudohypertrophic muscular dystrophy is the largest subgroup of the childhood dystrophies. The diagnosis of early neurologic injury is dependent on a total pediatric neurologic examination that usually includes an assessment of the primitive reflexes of the first year of life. Absent or highly persistent reflexes are usually indicative of abnormality.

The Cerebral Control of Speech and Language

This chapter discusses the cerebral control of speech and language. The mechanism for the human communicative nervous system is for the most part in the cerebrum. The cerebrum contains four lobes on its external surface: (1) the frontal, (2) parietal, (3) temporal, and (4) occipital lobes. A fifth, internal, lobe, the limbic lobe, plays a role in emotion and recent memory and may also be important in the motivation of communication. The insula historically has been considered a point of confluence of fibers traveling from the posterior portion of the brain to the anterior portion. The corpus callosum and the anterior and posterior commissures connect the two hemispheres and transfer information between them. Split-brain research after commissurotomy has dramatically demonstrated the asymmetrical functions of the two hemispheres. The left hemisphere is verbal, analytic, and logical; the right hemisphere is perceptual-spatial, intuitive, musical, and holistic. The language areas that were originally established clinicopathologically have been confirmed by newer neurodiagnostic methods. These language areas are richly supplied by cerebral arteries that join to form the circle of Willis at the base of the brain.

The Central Language Mechanism and Its Disorders

This chapter discusses the central language mechanism and its disorders. The exact neurophysiology of the central language mechanism is not completely known, but a model developed by Carl Wernicke over a century ago has proved to be the most valid and reliable construct for the explanation of the wide array of aphasia symptoms seen clinically. The model has gained wide acceptance among neuroscientists, linguists, and speech-language pathologists. There is growing support for the model from neurosurgical data, brain and CT scans, and other neurodiagnostic procedures. Although aphasic classification systems are abundant, the Wernicke model is the source of the most widely used current classification. Aphasias of the perisylvian zone include Brocas aphasia, Wernickes aphasia, conduction aphasia, and global aphasia. Aphasia syndromes outside the perisylvian speech zone are called transcortical aphasias. These include transcortical motor aphasia, transcortical sensory aphasia, mixed transcortical aphasia, and the isolated speech-area syndrome. Anomic aphasia is usually associated with bilateral lesions or mild involvement of the perisylvian speech area. Other anomic patients show no demonstrable lesions. Aphasia syndromes have often been dichotomized into fluent or nonfluent disorders in terms of spontaneous speech performance. Nonfluent aphasia is usually associated with anterior lesions and fluent aphasia with posterior lesions.

Neuronal Function in the Nervous System

This chapter discusses neuronal function in the nervous system. A neuron is the basic functional unit of the nervous system. Its primary property is excitability. The afferent processes of the neuron are called dendrites, and the efferent process is the axon. Neural transmission is a function basic to the nervous system, and the neuron with its processes serves as one of its basic conductive units. The synapse is a juncture point at which electrical impulses are transmitted from nerve to muscle, gland, or another neuron. Interneuron transmission occurs in the brain from nerve to nerve. Electrical transmission at the synapse is aided by the release of biochemical transmitters. Peripheral neuromuscular synapses release acetylcholine. Neuronal function at higher levels is accomplished in neuronal patterns and networks. The principles of network excitation and inhibition, convergence and divergence, and probabilistic selectivity of impulses at the synapse are important in brain function. There remains a significant knowledge gap between understanding the electrical and biochemical properties in neuronal transmission and explaining the neuronal activity necessary for speech and language.