The non-progressive perisylvian aphasias are common language disorders that follow focal, non-progressive cerebral cortical or subcortical injury to structures that occupy or adjoin the Sylvian fissure (areas supplied by the middle cerebral artery) most severely after damage to the left side of the brain. These disturbances constitute the most familiar and historically influential language disorders, including global aphasia, Broca aphasia, and Wernicke aphasia. The perisylvian aphasias share the inability to repeat (in contrast to the transcortical aphasias) but vary in the extent to which speech production and comprehension are differentially affected. These disorders are most often seen after stroke but can also follow other brain disorders, including traumatic brain injury, brain tumors, and various degenerative brain disorders. Interest is gaining with evaluating the effect and treatment of aphasia on real-world activity beyond what can be measured under restricted laboratory or clinical environments. In this article, the author explores contemporary and potential future approaches to treatment. The article also provides video vignettes from patients the author has personally evaluated to demonstrate these language disturbances.
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• Aphasia is a disturbance of only the symbolic aspects of language, whether expressive or receptive. The term does not apply to purely motor speech disorders (such as dysarthria) or to auditory disorders (such as hearing loss) that are not specific to language. Hence, as a central communication disturbance, aphasia disrupts not only speech, but also (but not invariably) reading and writing.
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• Aphasia is associated with diverse nonlinguistic cognitive disorders, which require further understanding whether nonlinguistic processes influence language deficits.
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• Aphasia is usually considered to follow left hemispheric injury rather than right hemispheric injury. Nonetheless, aphasia can also follow right hemispheric injury. The clinician should not automatically consider a patient with focal brain illness not to have aphasia simply because the illness involves the right cerebral hemisphere.
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• Evidence is gradually increasing to demonstrate several successful interventions for aphasia. Among the most vigorously pursued at present is transcranial electrical or magnetic stimulation to portions of the surviving cerebral cortex to improve left perisylvian function.
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• Research is starting to examine the effects of aphasia on spontaneous real-world communication beyond its effects on test results under restricted laboratory or clinic conditions.
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• Because the SARS-CoV-19 (COVID-19) illness can provoke cerebral infarction, aphasia is a possible consequence of this disease.
Historical note and terminology
Aphasia is the disordered use of words or sentences due to the impaired processing of their symbolic information content. The term is preferred when language disturbance is noticeably more severe than any other concurrent cognitive disorder in the same individual. It is distinguished from disturbances of hearing, voluntary oral control, memory, and attention that can impair communication. The term also does not apply to nonverbal aspects of vocal symbolic communication, such as emotional or musical intonation. Aphasia is used preferentially to describe impaired, immediately interactive communication involving speech or sign language (71), rather than recorded exchange (eg, written communication).
This article emphasizes aphasia in the adult (ie, following a typical adult-level acquisition of word knowledge and proficiency in sentence comprehension and production). The non-progressive perisylvian aphasias, ie, those that follow cerebral damage at or near the Sylvian fissure, have most frequently been described following stroke. Indeed, as many as 40% of stroke patients may be aphasic (44). Therefore, this overview emphasizes aphasic disturbances commonly encountered in clinical practice. However, the disturbances reviewed here may occur as well with other cerebral disorders that can progress relatively slowly, including brain tumors (08) and multiple sclerosis (114). Primary progressive aphasia is discussed in a separate article in MedLink Neurology.
Aphasia has been described for centuries (Benton and Joynt 1960; 299; 49). Formal clinical reports of aphasia appeared in the Russian literature in the late 18th and early 19th centuries (128). In the 1860s, French anthropologist Paul Broca associated expressive speech impairments with left frontal lobe injury that was evident at autopsy. He suggested, for the first time, that the left frontal lobe was essential for language (31). Marc Dax may have independently concluded the same, but refrained from publishing his findings (78). Subsequently, the German neurologists Meynert and Wernicke reported patients who spoke fluently but comprehended poorly (Wernicke 1874; 334). Wernicke distinguished receptive from expressive disorders. At about the same time, the English neurologist John Hughlings Jackson regarded the aphasic brain as a glass not partly empty, but partly filled. He was impressed by the retained language functions in even profoundly aphasic individuals, their considerable performance fluctuation during a single examination, and especially the preservation of "automatic" speech (ie, well-learned expressions such as greetings and curses prompted by the particular context) relative to "propositional" speech (the creation of new expressions) (79). Subsequently, Jackson learned that François Baillarger in France had independently, and somewhat earlier, identified the same phenomenon; therefore, he termed this the “Baillarger principle” (111).
Broca's and Wernicke's findings inspired other investigators, many of whom were German, to develop language models based on the interaction among spatially and functionally discrete cerebral regions. However, interest in the 19th century German aphasia models faltered by the early 20th century, perhaps due to the stigma of Germany's defeat in the first World War (119). Simultaneously, Jackson’s writings failed to gain greater acceptance, perhaps because his works were difficult to read (79). The advent of psychoanalysis and personality theories, and the abandonment of surgery for mental illness later in the 20th century, may have overshadowed interest in human focal cognitive disturbances in general. Inspired by Myers and Sperry’s finding of specific cognitive disorders in laboratory animals following experimental interhemispheric disconnection, the American neurologist Norman Geschwind revived Wernicke's intrahemispheric disconnection model in an extensive review (123; 120). Through his influential cognitive disorders training program, aphasia became a leading neurologic topic in the present era. A comprehensive historical overview of research on aphasia, including technological advances in understanding its neurologic mechanisms and recovery, is provided by Hillis (151).
Broca termed the language disturbance "aphemia." However, in 1864, his more esteemed colleague Armand Trousseau criticized the term due to its Greek connotation of "infamy" and advocated "aphasia" instead (103; 273), which from then on became the standard term for acquired language disorder. Today "aphemia" is seldom used, but generally describes chronically impaired speech with intact comprehension and writing (04; 279; 05). “Dysphasia” is a frequently used alternate term for aphasia, particularly among British scholars.
Numerous classifications and terms have been proposed for aphasia subtypes, without universal acceptance. Generally, clinicians understand the following classifications, despite the controversies. Fluent aphasia refers to a language disorder with effortless speech production; nonfluent aphasia indicates a language disorder with halting, effortful speech production. Both may involve impaired comprehension and speech. Therefore, the terms receptive (or sensory) aphasia and expressive (or motor) aphasia should be discouraged (221; 338), because seldom (if ever) does one identify a purely expressive or receptive disorder (176). Broca aphasia describes effortful production, loss of grammatical modifications, and relatively preserved comprehension. Wernicke aphasia denotes fluent speech typified by circumlocution and neologisms, and is classically associated with more severe comprehension impairment. Conduction aphasia indicates minimally disturbed comprehension and expression, but with relatively impaired repetition. Global aphasia (or severe aphasia, total aphasia) indicates profoundly impaired general language functions with minimally deficient other cognitive functions.