Behavioral & Cognitive Disorders
Dementia associated with amyotrophic lateral sclerosis
Aug. 11, 2023
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The author describes language and communication deficits associated with right hemisphere brain damage due to, for example, cerebrovascular accident or traumatic brain injury. Topics include nonliteral language, such as metaphor and irony, humor, and theory of mind (ToM). In addition to symptom descriptions, the author presents a historical background, points out that impairments associated with right hemisphere brain damage extend beyond just communication, and describes some approaches to treatment. The author also presents evidence that the intact right hemisphere makes substantial contributions to communication, but the strong claim that the right hemisphere is “dominant” for specific language functions is not well supported.
• Damage to the right cerebral hemisphere can impair communication ability, even in the absence of obvious aphasia.
• Communication deficits associated with right hemisphere injury involve nonliteral language (eg, metaphor, irony, and indirect requests), speech prosody, discourse (eg, humor and story comprehension), and related cognitive abilities, such as inference, working memory, and Theory of Mind (ToM; ie, making inferences about the beliefs and emotions of other people to interpret their behavior).
• Not all patients with right hemisphere brain damage exhibit pronounced symptoms.
• Most of the impairments associated with right hemisphere brain damage are not clearly localized. They are associated with injury to different regions within the right hemisphere and with injury elsewhere in the brain, and are also associated with various etiologies, including traumatic brain injury and placement on the autism spectrum disorder.
• There are assessment batteries and a limited number of evidence-based treatment protocols available for communication impairments associated with right hemisphere brain damage.
Descriptions of the effects of right hemisphere brain injury on communication started to appear with increasing frequency in the last few decades of the 20th century, approximately 100 years later than modern descriptions of aphasia subsequent to left hemisphere brain damage (12; 24). The primary role of the left cerebral hemisphere for language in adult humans has not been challenged. Virtually all discussions of phonetic, phonological, lexical, and syntactic impairments revolve around left hemisphere injury. However, language and communication in natural settings involves considerably more than the “nuts and bolts” of the basic building blocks of literal language that are sensitive to left hemisphere brain damage. A patient can score well on most parts of an aphasia battery but still fare very poorly in natural communicative settings that require supralinguistic competence, such as appreciation of context, inferential ability, and understanding an audience. The nuances conveyed by nonliteral language, such as metaphor and irony, the meaning indicated by speech prosody, and the apprehension of a speaker’s main point in a story or conversation, underscore the relevance of the much wider range of language and language-related skills that are often affected by right hemisphere brain damage. The term “right hemisphere syndrome” is sometimes used as a label for the collection of deficits associated with right hemisphere brain damage. Consideration of the right hemisphere’s contribution to language and related cognitive domains provides a richer understanding of healthy and impaired communication.
This article does not cover aprosodia associated with right hemisphere brain damage because aprosodia is discussed in detail in a separate article.
Interest in right hemisphere language has increased steadily since the 1980s but has roots in previous work. The neurologic literature addressing visuospatial processing, attention, and unilateral spatial neglect in patients with right hemisphere damage is extensive (29). The importance of right hemisphere structures for emotion is well established (43; 74). Other work extends the range of impairments to include neurologic, emotional, and psychosocial (22). Weinstein and Kahn’s monograph on anosognosia highlighted the odd lack of insight exhibited by some patients (77; 63). Eisenson provides a first description of verbal production deficits in patients with right hemisphere brain damage (17).
Gardner and colleagues were among the first to investigate how right hemisphere brain damage might limit patients’ semantic processing in studies that led directly to later work. For example, Gardner and Denes described right hemisphere brain damaged patients’ difficulty with connotative meaning expressed in pictures: patients had trouble choosing an appropriate pictorial analog for a concept such as “wealth” from an array that included an arrow pointing up and another arrow pointing down (23). Winner and Gardner reported a related tendency to be concrete: when asked to select an appropriate picture to represent the meaning of a familiar metaphor (“heavy heart”), they would choose a man staggering under the weight of an oversized heart rather than a picture of a man crying (78). Since then, investigation of right hemisphere brain damage patients’ communication impairments has yielded an extensive catalogue of abnormalities (34; 66; 53; 40). In recent years, the catalog of deficits relevant to language and communication has expanded to include social and cognitive impairments tied to, for example, Theory of Mind (ToM), as will be discussed below.
The literature leaves some broad issues unresolved. One question is whether a single core problem can account for a range of impairments. Beeman, for example, proposes that the right hemisphere plays a relatively large role in “coarse-grained” processing (03). A second question is whether regions within the right hemisphere act as “centers” with primary responsibility for specific types of processing or, alternatively, whether a region simply contributes to normal levels of competence. Deficits can result from right hemisphere brain damage under either interpretation. A third issue is how the right hemisphere’s processing strengths combine with those of the left hemisphere to support normal communication. Although definitive answers to these questions are not available, a systems perspective is already well represented (64; 37; 52; 60; 15).
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