Clinical manifestations

Presentation and course

Individuals can exhibit any subset of “right hemisphere syndrome” subsequent to focal lesions in the right hemisphere or subsequent to other etiologies. For stroke patients, communication deficits may not be obvious on bedside testing, depending on the focus of the examiner, and may be overshadowed by, for example, hemiplegia or dense left neglect. Families may also have trouble articulating exactly what is not “normal” about the patient because the deficits can be subtle and variable; problems with nonliteral language, for example, will not be obvious if a speaker uses mostly simple, direct sentences. However, over time, communication deficits similar to those described below will result in social awkwardness that undermines a patient’s success in the workplace and within the family.

Stories and humor. Discourse is a broad term that often refers to connected sentences or utterances that form a larger unit, such as a story or conversation. One key feature is that the main point of discourse may be different from the sum of the individual sentence meanings. Another key feature is that understanding the main point requires a variety of resources and skills that can be affected by brain injury, including working memory, the ability to make inferences, understanding nonliteral language, and an appreciation of other people’s goals in a conversation as well as their knowledge.

One form of discourse consists of narratives, eg, stories. Early work revealed that patients with right hemisphere brain damage did not understand stories despite their comprehension of individual sentences. Wapner, Hamby, and Gardner suggested that patients with right hemisphere brain damage could report details of a story such as a fable but often failed to grasp the moral or main point (75). Joanette and colleagues established the general finding with a careful analysis of patients’ story recall (35), and studies by Hough extended the finding using shorter passages (33). Patients with right hemisphere damage also perform worse than controls at making logical and pragmatic inferences from stories depicted in pictorial stimuli (58). The basic finding that has been reported often is that right hemisphere brain-damaged patients’ understanding represents details and disparate elements but does not adequately reflect the inferences needed to apprehend main themes.

Because verbal narratives necessarily extend over time, part of the deficient performance by patients with right hemisphere brain damage might be secondary to problems with working memory and, for that reason, may not be specific to discourse. Tompkins and colleagues have shown that working memory limitations are relevant to understanding severity of impairment in patients with right hemisphere brain damage: patients with less working memory capacity perform worse on discourse-related tasks (70). The explanatory value of general cognitive disability, such as decreased working memory among others, is a critical avenue to pursue to determine exactly how much of a patient’s poor performance can be accounted for within a general cognitive perspective. There is, however, also evidence suggesting that the narrative comprehension deficit cannot be explained entirely in terms of working memory. For example, Myers and Brookshire asked patients with right hemisphere brain damage to explain Norman Rockwell paintings (54). Patients with right hemisphere brain damage exhibited abnormal output that missed the gist of a painting, even when working memory demands were reduced by having a painting in view.

Other work on narrative discourse used humor as a vehicle (61). The use of humor as a type of stimulus material was motivated in part by affective changes sometimes seen after right hemisphere brain damage; however, humor also provides convenient ways to manipulate discourse variables. Brownell and colleagues asked patients with right hemisphere brain damage to complete short story jokes by choosing the correct punchline from a set of alternatives (09). The main result was that the patients with right hemisphere brain damage appeared to understand that jokes as a narrative genre required a punchline that was incongruous—that did not follow from the body of the joke in a straightforward manner. However, the patients were deficient with respect to the second requirement: inferring how a punchline actually fit with the joke on a second level of interpretation. The patients with right hemisphere brain damage showed difficulty discriminating between a nonsense ending that was simply out of place and a joke’s correct punchline that was both surprising and coherent if reinterpreted to fit with the beginning of the joke.

Brownell and colleagues reported an analogous inference deficit using nonhumorous 2-sentence vignettes such as the following (10):

Reading just the first sentence led to the interpretation that Sally was seeking an autograph. After reading the second sentence that forms part of the same discourse unit, non-brain-damaged controls revised their interpretation to identify Barbara as a journalist. Patients had trouble with the revision and did not readily abandon their view of Sally as interested in autographs. The need for revision was present in jokes and in nonhumorous items, which places the likely account in the domain of all discourse rather than just humor. This result can be seen as an accentuated version of right hemisphere brain-damaged patients’ disinclination to work to integrate elements into a whole that makes sense of all the parts. Although patients with right hemisphere brain damage can integrate meaning across sentence boundaries in some situations, they often appear satisfied with (or limited to) considering each sentence on its own in a linear fashion without building a mental model of an entire story (44).

Nonliteral language. Other reports discuss the most frequently cited language symptom of patients with right hemisphere brain damage: their tendency to be literal. In one representative study, Van Lancker and Kempler asked patients with right hemisphere brain damage (and also aphasic patients with left hemisphere brain damage) to choose a picture to illustrate the meaning of common idioms such as “turning over a new leaf” (73). The basic finding was that patients with right hemisphere brain damage (but not aphasic patients with left hemisphere brain damage) tended to choose literal depictions (a man raking a leaf) rather than the figurative meaning (a man throwing a bottle of liquor into a trash can). Aberrant comprehension of even familiar phrases (eg, “heavy heart,” “turning over a new leaf”) illustrates the dense nature of the impairment for some patients. This basic result has been demonstrated in many studies and has been elaborated using single-word stimuli (11). The extension of the basic impairment to single words is valuable in large part because some researchers have capitalized on the flexibility of word stimuli to explore a variety of explanations for many right hemisphere brain damage symptoms using various patient populations and noninjured populations. One summary is that the right hemisphere appears particularly important for “coarse-grained” semantic processing, that is, for generating and maintaining weak or diffuse associations between words that could provide a basis for understanding extensions of word and phrase meaning and, perhaps, understanding the gist of longer discourse units (03).

Right hemisphere brain damage affects patients’ interpretation of indirect requests and irony, which together illustrate the role of context in guiding whether a sentence is intended literally or nonliterally. The pervasiveness of requests and other nonliteral utterance types signals how significantly impairments can limit a patient’s social success, in part because of social conventions governing what is considered polite behavior (06).

Several authors have examined request comprehension and, to a lesser extent, production by patients with right hemisphere brain damage (20; 62). The main conclusion is that patients exhibit decreased use of conversational context as a guide, even though they are capable of recognizing and using some elements of requests. For example, a conventional request frame in American English is “Could you open the window?” The speaker’s intent is not to inquire about the ability to open a window; the intent is requesting the listener to open the window. Another conventional request marker is the use of “please.” Patients with right hemisphere brain damage fare better with such familiar request signals (08). They are less skilled at using implicit social and linguistic context to guide interpretation. Stemmer and colleagues, for example, varied factors such as the relative social power or status of a speaker and listener (62). A low-status speaker can use an indirect form to request something of a high-status listener without offending.

Difficulties understanding sarcasm, irony, and metaphor provide other examples of the problem (60; 16). One sees the joint effects of inattention to context and a tendency towards literal interpretations (13). The contextual factors that support irony are different from those most relevant to indirect requests but are most likely analogous with respect to how patients with right hemisphere brain damage consider them. For example, a particular utterance, “I am so glad the sun is shining,” can be used ironically on a day with miserable weather or literally on a beautiful summer’s day. As will be discussed below, more recent work has sought to account for deficits in irony under the rubric of general, extralinguistic impairments.

Question-asking. Another pragmatic aspect of communication is its use to gather information. Minga and colleagues studied question-asking in patients with right hemisphere brain damage relative to healthy adults and found that question types differed between the two groups: patients were more likely to ask content questions and less likely to ask polar (yes-no) questions than controls (49). In a follow-up study comparing question-asking between patients with right hemisphere damage and controls during a more naturalistic conversation, the patients asked fewer questions of any type, overall (48). Patients’ question-asking in this study was associated with measures of executive function and visuospatial skills. These studies suggest that appropriately and efficiently structuring a conversation to learn new information from a communication partner is another aspect of the pragmatic language deficits stemming from right hemisphere damage. Following along with a conversational topic and recognizing when it is one’s turn to speak are related conversational skills that may be impaired with right hemisphere damage (41).

Cognitive factors underlying communication deficits. Right hemisphere brain damage can also undermine successful communication indirectly. Working memory was mentioned above as an important resource for language understanding. Similarly, competence in Theory of Mind (ToM; using the thoughts, beliefs, and emotions of others to understand their behavior) supports a great deal of language use in context (60; 42; 76). (The MedLink Neurology article Theory of Mind provides further detail.) One important distinction is between first- and second-order beliefs. For example, a person named Allen might arrive at work very early on a beautiful spring day. While inside the office building without access to windows, Allen would not realize that the weather had changed to a dark, rainy day with gusts of wind. Allen would, therefore, have a false first-order belief about the weather. If Allen spoke about the weather to a coworker, he might utter a literally false statement such as, “This weather is really nice.” That would be a mistake but neither deceptive nor ironic in intent. Second-order beliefs rest on one person’s beliefs about another person’s beliefs and provide a foundation for how to interpret utterances in context. Imagine another speaker, Brenda, who arrives at work late during a period of heavy rain. Talking to another person walking into the building with her, Brenda might utter, “This weather is really nice,” with ironic intent: Brenda knows that her listener also knows that it is raining and can use a literally false statement to convey her point with added emphasis. On the other hand, if Brenda talks to Allen, she will need to assess whether Allen knows about the change in weather. If Brenda knows that Allen’s information is outdated, she could even lie to him by saying, “This weather is really nice.” Depending on Brenda’s specific second-order beliefs about Allen, she might use an utterance to accomplish different conversational goals.

Impairments in working memory and other aspects of executive function at least partially account for impaired ToM due to the amount of information that must be retained and updated, especially with second-order beliefs (55; 72). There are, however, studies that support a dissociation between ToM and other, general cognitive domains, which suggests that ToM impairments cannot be reduced entirely to general cognitive dysfunction (45). Happe and colleagues used single frame cartoons to increase control over extraneous task demands (28; 25). Patients with right hemisphere brain damage (but not aphasic patients with left hemisphere brain damage) showed selective impairments in understanding cartoons based on ToM and better performance on a control condition that used cartoons based on humor that did not require ToM. It is also relevant that several studies with non-brain-injured subjects support the separation between ToM and other more general components of cognition, such as working memory and other aspects of executive function (59).

Prognosis and complications

Research to address prognosis and assessment of right hemisphere language and communication disorders is still at an early stage (57). Communication deficits after a right hemisphere stroke do seem to influence social relationships and social network size (30), conversation patterns with close social partners (02), and overall social participation (31). These might be important points to consider when designing interventions.

Biological basis

Etiology and pathogenesis

The communication impairments mentioned above are associated with brain injury due to various causes (cerebrovascular accident, tumor, closed head injury, etc.). Precise localization of lesion within and to the right hemisphere is missing from many studies. A good portion of studies compare group performance of patients with right hemisphere brain damage to that of non-brain-damaged control groups because, often, the linguistic demands of the experimental tasks are too great to allow testing of patients with left hemisphere brain damage and significant aphasia. In addition, several studies have documented that impairments observed in patients with right hemisphere brain damage can be seen in patients with traumatic brain injury that affects frontal regions bilaterally (14) and also in individuals with diagnoses such as autism spectrum disorder and schizophrenia (27; 52).

However, some studies have compared individuals with left and right hemisphere damage directly on language and communication tasks. One study confirmed that patients with right hemisphere damage produced less typical interpretations of the meaning of scenes depicting social interactions, compared to healthy controls as well as patients with left hemisphere damage (01). Another study attempted to isolate areas in the right hemisphere that may be key players in the language deficits specific to right hemisphere damage (21). Patients with right hemisphere stroke who were presented with auditory sentence-to-picture matching showed more damage specifically to the right inferior frontal sulcus, when compared to patients with right hemisphere stroke who did not show impairment in this comprehension task (and left hemisphere stroke patients). A follow-up experiment on healthy controls found that the right inferior frontal sulcus was active during the sentence matching task as well as a working memory task. This study suggests that right hemisphere damage can have significant impact on language comprehension, possibly related to language-specific executive function deficits, when the inferior frontal sulcus is damaged (21).

One safe generalization is that much of the processing disrupted in patients with right hemisphere brain damage involves the participation of many brain regions, including, but not restricted to the right hemisphere (61; 64; 38; 18). Nonetheless, clinically important communication deficits are associated with right hemisphere dysfunction. A communication function that is not mediated primarily by the right hemisphere may still require participation by the right hemisphere to achieve normal levels of performance. The clinical importance of the “right hemisphere syndrome” persists, even as our understanding of how language function requires coordination among bilaterally distributed systems. In this article, a liberal criterion has been applied for including a function under the umbrella term “right hemisphere language”: that the function is disrupted by right hemisphere brain damage or that functional imaging suggests a role for the right hemisphere.

Neurologic or radiologic evidence for injury to the right hemisphere or the prefrontal regions bilaterally suggests that communication deficits may affect a patient’s prognosis.

Epidemiology

Most of the literature on right hemisphere language consists of what might be considered demonstration studies: studies that show that deficits can be documented in a subset of patients with right hemisphere brain damage but that offer little information on the incidence in the population of patients having suffered some form of neurologic event affecting the right hemisphere. Much of the seminal work on right hemisphere language was based on examination of small groups of adult patients who experienced cerebrovascular accidents and had sustained unilateral, focal damage affecting some portion of the middle cerebral artery distribution. Further, research subjects were most often recruited from rehabilitation settings and exhibited chronic cognitive or physical impairments. The studies, thus, do not speak to the probability that a particular lesion will result in a specific impairment. Estimates for the incidence of some portion of the “right hemisphere syndrome” in stroke patients with right hemisphere brain damage vary from roughly 50% to 78% (19).

Prevention

Risk factors for stroke or other etiologies of brain damage are important in this context.

Differential diagnosis

Right hemisphere syndrome can result from any of a variety of etiologies that cause illness to the brain.

Confusing conditions

It is important to differentiate right hemisphere language deficits from aphasia. Aphasia could mask a right hemisphere language disorder in a case of damage to both hemispheres, indicating the importance of doing both standard tests for aphasia as well as tests to uncover pragmatic language difficulties (eg, discourse analysis, tests of pragmatic language). It is worthwhile to note that the behaviors typical of right hemisphere language disorders can also follow left hemisphere damage but are perhaps underreported due to overlying aphasia. Some researchers have suggested that pragmatic language is not as localized to the right hemisphere as has been thought and that the two hemispheres interact in pragmatic language comprehension (39; 79).

Right hemisphere damage can also lead to aprosodia, which can appear along with the difficulties in pragmatic communication, contextual comprehension, and other language deficits described here. However, different types of aprosodia have also been noted with other conditions (eg, autism spectrum disorders, traumatic brain injury).

General inattention or disorders of attention could also be confused for right hemisphere language disorders, again highlighting the need for holistic assessment to determine whether patients consistently display signs of pragmatic language and communication difficulties.

Diagnostic workup

There are several test batteries designed for assessing communication impairments associated with right hemisphere brain damage (56; 36; 26). However, a study found that speech-language pathologists tended to use standardized assessments for cognitive impairments following right hemisphere stroke, but often only informally assessed communicative impairments or did not assess at all. Evidence-based treatments were also reported to be more likely used for cognitive than communicative impairments (57). Even when given, standard language deficit tests can miss some of the language deficits in both left and right hemisphere language disorders, which emphasizes the importance of a comprehensive and sensitive battery of tests (47).

To address difficulties in assessment and treatment of right hemisphere language disorders, Minga and colleagues have created an open database of video-recorded and transcribed interactions of individuals with right hemisphere damage and controls, which is called RHDBank (50).

Management

Compared to the array of treatment protocols designed for speech and language disorders associated with left hemisphere injury, there are relatively few treatment protocols designed for right hemisphere language impairments (05). One constraint is that the impairments associated with right hemisphere brain damage are often less well defined in both theoretical and functional terms than are the symptoms associated with aphasia. There are, however, guidelines and directions that can be usefully followed (66; 53; 04; 19). Some preliminary efforts to provide evidence-based treatment options have grown directly out of earlier work. These protocols also represent different approaches.

Lundgren and colleagues describe a training program that emphasizes practice making explicit semantic judgments as a means to improving oral metaphor interpretation in patients with right hemisphere brain damage (46; 07). The staged protocol is based on a simple analysis of metaphor: two nouns from different semantic domains share associations. For example, the metaphor “my job is a prison” consists of the two nouns “job” and “prison.” Although the two nouns have several associations that are not held in common, they share other associations: confinement, limits, unpleasantness, no escape, etc. The training has patients practice generating associations, evaluating associations, and identifying potential shared associations that could form a metaphor. One distinctive feature of the program is the use of simple graphic depiction of associations that greatly reduces memory demands, keeps patients focused, and supports practice. Preliminary results show that metaphor interpretation improves substantially and selectively coincident with the onset of treatment.

Tompkins and colleagues have used a different approach to treatment based on the previous literature documenting problems with suppression of meaning and coarse coding (65; 68; 71; 69). The strategy for Contextual Constraint Treatment is to capitalize on remaining strengths of patients with right hemisphere brain damage by using tasks targeting implicit or automatic processing rather than tasks requiring explicit metalinguistic judgments and by relying on contexts that bias interpretations without requiring revision or difficult inferences. Preliminary results were encouraging. Tompkins emphasizes the importance of clinical recognition of the heterogeneity of patients with right hemisphere language and communication impairments for considering treatment options, as well as sensitivity to lack of insight in patients when considering measurement via self report (67).

Minga and colleagues, the authors who established the RHDBank of transcripts from individuals with right hemisphere brain damage, studied whether “apragmatism” might an appropriate and useful term for the cluster of language deficits experienced by these individuals (51). A review by an international group of experts suggested that the diagnostic label was suitable, and its features were operationalized using RHDBank. The authors suggest that this label might improve consistency in describing and understanding right hemisphere language disorders as well as improve research and treatment.

Outcomes

Elements of the “right hemisphere syndrome” can be improved by treatment. However, there is a lack of data on maintenance of treatment gains over the long term, as well as a lack of data on recovery patterns of right hemisphere language impairments. Although communication deficits that follow right hemisphere stroke have not by themselves predicted rehabilitation outcomes, the severity of communication deficits did predict rehabilitation outcomes (32).