Speech and language disturbances in atypical parkinsonian disorders often present as initial symptoms or prominent neurobehavioral sequelae that worsen as the disease progresses. These disorders, even in their early stages, can have profound effects on communicative functioning and, by extension, psychosocial well-being. In the face of neurodegenerative disease, the downward course of the ability to communicate mirrors a loss considered elemental to the human condition; it unavoidably robs the individual of a primary mode of expression of thoughts and ideas and, in its most severe form, basic needs.
We draw a distinction between speech and language for purposes of clarity throughout this chapter. These terms, sometimes used interchangeably or in combination by clinicians and researchers, can be defined and distinguished in a hierarchical representational framework (1):
Overview of Neuroanatomical Correlates
If approached from the perspective of classical neuroanatomical correlates, damage to portions of the auditory and visual association areas of the cortex can result in comprehension deficits of the spoken or written word. Damage to Wernicke's area (Brodmann area 22), in the posterior portion of
From: Current Clinical Neurology: Atypical Parkinsonian Disorders Edited by: I. Litvan © Humana Press Inc., Totowa, NJ
the superior temporal gyrus of the dominant hemisphere, can result in a type of aphasia generally called Wernicke's aphasia. Wernicke's aphasia is marked by reduced comprehension and fluent but often paragrammatic verbal output characterized by word or nonword substitutions (paraphasias) sometimes to the extent of producing fluent streams of non-English or neologistic jargon. In contrast, damage to Broca's area (Brodmann areas 44-45), in the third convolution or inferior gyrus of the frontal lobe of the dominant hemisphere can result in a type of aphasia generally called Broca's aphasia. Broca's aphasia, in contrast to Wernicke's aphasia, is marked by relatively spared comprehension but sparse, effortful, nonfluent, and agrammatic verbal output. Along the parameters of fluency, comprehension, repetition, and naming, other classic aphasia syndromes have been identified including conduction, transcortical motor, transcortical sensory, and global aphasia.
The nondominant hemisphere is also increasingly implicated in its role in language functions, particularly for global and thematic processing of narratives, pragmatics (relation between language behavior and context in which it is used or interpreted), and prosody (elements of speech melody, rate, stress, juncture, and duration) of language, and inferencing, coherence, and topic maintenance during discourse processing and production (3,4).
Skilled motor programs for control of the larynx, lips, mouth, respiratory system, and other accessory muscles of articulation are thought to be initiated from Broca's area. Damage to this area, or within other parts of the left hemisphere's network of structures involved in the planning and programming of speech, results in apraxia of speech. Once these programs are activated via the premotor zone of Broca's area, thus mediating orofacial and speech praxis, the facial and laryngeal regions of the motor cortex (bilaterally) activate the speech musculature for actual emission of sound. The neural substrates of neuromuscular execution originate in the primary motor cortex (Brodmann area 4) with pathways descending either directly or indirectly via the pyramidal or extrapyramidal tracts. The pyramidal tract consists of upper motoneurons in the cerebral cortex with axons coursing through the pyramidal tract in the medulla and terminating on anterior horn cells or interneurons in the spinal cord. The pyramidal tract is composed of the corticospinal tract and the corticobulbar tract that influences cranial nerve activity. Types of dysarthria that could result (e.g., spastic dysarthria) would have features of spasticity, increased muscle stretch reflexes, and clonus. In contrast, damage to lower motoneurons from spinal and cranial nerves results in loss of voluntary and reflex responses of muscles. The result would be hypotonia and absence of muscle stretch reflexes. Paralysis and atrophy would occur, with the early stages of atrophy resulting in fibrillations and fasciculations. Dysarthrias with damage to lower motoneurons would have characteristics of flaccidity (e.g., flaccid dysarthria) (5). Other pathways that, if interrupted, would result in dysarthria, include extrapyramidal (coursing through structures of the basal ganglia) and cerebellar motor pathways, which could result in hyper-kinetic or hypokinetic components following extrapyramidal damage, or ataxic dysarthria following cerebellar damage (see Appendix A for descriptions of aphasia syndromes, apraxias, and dysarthria types; Appendix B for case descriptions and test stimuli used for audio samples of speech and language disorders that accompany this chapter).
With advances in neuroimaging techniques, a dynamic systems rather than localization view of speech and language functions is being adopted. Neuroimaging findings have shown that language processing extends beyond the classical perisylvian region containing Broca's and Wernicke's areas and depends on many neural sites linked as systems. For example, both left temporal and prefrontal/ premotor cortices have been found to be activated by language processing, and do so selectively. Neuroimaging studies have also shown that structures in the basal ganglia, thalamus, and supplementary motor area are engaged in language processing (6). Adding to the evidence of functional connectivity, a recent study suggests that the anatomical and functional organization of the human auditory cortical system points to multiple, parallel, hierarchically organized processing pathways involving temporal, parietal, and frontal cortices (7). Computational mapping methods, which can combine probabilistic maps of cytoarchitectonically defined regions with functional imaging data, hold promise for further elucidating brain region specialization. For example, Horwitz et al. (8). found that BA 45, not BA 44, is activated by oral or signed language production, implicating BA 45 as the part of Broca's area that is fundamental to the modality-independent aspects of language generation.
In order to clinically assess or scientifically examine aspects of speech and language, the clinician or researcher employs a battery of instrumental and behavioral tests or experimental tasks that tap both isolated and integrated components of speech and language. This approach is intended to determine relative strengths and weaknesses necessary for differential diagnosis, and to assess the consequential effects of specific disturbances on functional communication in daily life contexts. Therefore, a clinical battery is best composed of diagnostic instruments that measure the fine-grained features of speech or language, and functional measures of communication that address speech or language as an integrative construct in the context of daily life activities. In line with contemporary models of health and disability that encompass both biophysical and psychosocial aspects of medical intervention (e.g., World Health Organization International Classification of Functioning, Disability and Health; see ref. 9). Clinicians and researchers are also extending clinical measurement to aspects of general wellness or quality of life in order to determine the effect of an impairment or activity limitation on social participation, autonomy, and self-worth.
Specific to language, behavioral measurement (online automated tasks that capture aspects of processing or production as they occur in real time; standardized paper-and-pencil tests) typically includes assessment of aspects of spontaneous speech, comprehension of oral and written language, repetition of words and phrases of increasing length, naming of objects and actions, and writing. Assessment of these parameters allows differential diagnosis of aphasia, either as a classical syndrome or as a constellation of deficits that point to specific neuropathological processes.
Assessment of speech typically is conducted via a combination of perceptual, acoustic, and physiologic methods (1). Perceptual methods are based primarily on auditory-perceptual attributes that allow clinical differential diagnosis. Acoustic methods contribute to acoustic quantification and description of clinically perceived impaired speech and confirm perceptual judgments of, for example, slow speech rate, breathy or tremulous voice quality, vocal pitch and loudness variations, hypernasal resonance, and imprecise articulation. Their ability to make visible and quantify the speech signal can be used as baseline data or as an index of stability or change. Physiologic methods focus on characterizing the movements of speech structures and respiratory function, muscle contractions that generate movement, temporal parameters and relationships among central and peripheral neural activity and biome-chanical activity, and temporal relationships among active CNS (central nervous system) structures during the planning and execution of speech (for comprehensive reviews of assessment methods, see ref. 1 for motor speech disorders; refs. 10 and 11 for aphasia and related neurologic language disorders; refs. 4 and 12 for right-hemisphere communication disorders; ref. 13 for functional communication and psychosocial consequences of neurologic communication disorders).
Our purposes here are to characterize the atypical Parkinsonian disorders of corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), multiple systems atrophy (MSA), and dementia with Lewy Body disease (DLB) from the perspectives of speech and language. For each diagnostic group, we: (a) describe the neuroanatomical correlates of speech and language disorders, (b) identify their clinically common and differentiating features on the bases of clinical assessment and clinical research findings, and (c) offer some clinical management suggestions. We end by suggesting some directions for future research. Table 1 abstracts the common and distinctive features of speech and language disturbances across diagnostic groups.
Common and Differentiating Features of Speech and Language by Diagnostic Group
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