The right hemisphere is not unitary in its role in aphasia recovery

Neurologists and aphasiologists have debated for over a century whether right hemisphere recruitment facilitates or impedes recovery from aphasia. Here we present a well-characterized patient with sequential left and right hemisphere strokes whose case substantially informs this debate. A 72-year-old woman with chronic nonfluent aphasia was enrolled in a trial of transcranial magnetic stimulation (TMS). She underwent 10 daily sessions of inhibitory TMS to the right pars triangularis. Brain activity was measured during picture naming using functional magnetic resonance imaging (fMRI) prior to TMS exposure and before and after TMS on the first day of treatment. Language and cognition were tested behaviorally three times prior to treatment, and at 2 and 6 months afterward. Inhibitory TMS to the right pars triangularis induced immediate improvement in naming, which was sustained 2 months later. fMRI confirmed a local reduction in activity at the TMS target, without expected increased activity in corresponding left hemisphere areas. Three months after TMS, the patient suffered a right hemisphere ischemic stroke, resulting in worsening of aphasia without other clinical deficits. Behavioral testing 3 months later confirmed that language function was impacted more than other cognitive domains. The paradoxical effects of inhibitory TMS and the stroke to the right hemisphere demonstrate that even within a single patient, involvement of some right hemisphere areas may support recovery, while others interfere. The behavioral evidence confirms that compensatory reorganization occurred within the right hemisphere after the original stroke. No support is found for interhemispheric inhibition, the theoretical framework on which most therapeutic brain stimulation protocols for aphasia are based.     

Language recovery in aphasia: A right hemisphere perspective

Abstract

Recovery of language function following brain injury has been attributed to various phenomena including spontaneous recovery of function, reduction of physiological symptoms (for example, reduced oedema), and to the transfer of function to surrounding cerebral structures. These explanations have been based on the concept of the left hemisphere as the sole processor of language. The present article reviews the research findings which provide evidence to support a hypothesis of right hemispheric compensation as one of the major mechanisms for language recovery/compensation in many aphasic patients.     

The role of the left and right hemispheres in recovery from aphasia

Abstract

The respective contributions of the left and right cerebral hemispheres in the recovery from aphasia are a matter of debate. This paper is devoted to a review of several different sources of related clinical and experimental evidence: bilateral lesion cases, laterality studies in aphasics, neurophysiological and neuroimaging investigations. The data collected with these different approaches provide converging evidence for the contribution of both hemispheres to the process of language recovery. Time post-onset, as well as a number of lesion-related and individual differences, modulate the relative contribution of each hemisphere in the individual case.     

Suggestive evidence for an involvement of the right hemisphere in the recovery from childhood aphasia: a 3-year follow-up case study

We describe the case of an 11-year-old, previously healthy, pre-puberal, right-handed girl with acquired aphasia following an extensive cerebral hemorrhage into a left hemisphere brain tumor. A 3-year follow-up evaluation of the girl's communicative performance showed an incomplete recovery of linguistic abilities with a good recovery of comprehensive components, but persisting severe impairment in expressive language. At the end of the follow-up period, with the aim of assessing the lateralization of some linguistic abilities, we carried out an experimental investigation using tachistoscopic reading and object naming tests along with a dichotic listening test. All these tests showed a clear left field/left ear-right hemisphere advantage. We discuss both clinical and experimental results with regard to implications for the linguistic abilities of the right hemisphere in late versus early childhood and its interaction with aetiology in the recovery from acquired childhood aphasia.     

Jargonagraphia with severe aphasia due to a right hemisphere lesion: case report.

The authors report a case of a patient who developed jargonagraphia, severe aphasia, unilateral spatial neglect and apraxia due to a right hemisphere lesion. Jargonagraphia with severe aphasia, unilateral spatial neglect and apraxia is quite rare. The mechanisms of jargonagraphia remain unknown. A possible mechanism underlying this case of jargonagraphia is discussed.     

Effectiveness of melodic intonation therapy in a case of aphasia following right hemisphere stroke

Background: The use of Melodic Intonation Therapy (MIT) in the clinical setting is suggested to be based on several criteria; however, some persons with aphasia not meeting these criteria may still benefit from this approach.

Aims: The purpose of this research was to explore the effectiveness of utilising MIT to improve expressive language in a person with global aphasia following right hemisphere stroke.

Methods & Procedures: A participant with global aphasia following right hemisphere haemorrhagic stroke completed a 7-week treatment programme utilising MIT. Sessions were held 5 days a week, for two and a half hours per day. Non-linguistic cognitive activities (COG) were also utilised briefly in each session as a break (BRK) from MIT. The Aphasia Diagnostic Profiles (ADP), American Speech-Language-Hearing Association-Functional Assessment of Communication Skills and the Stroke and Aphasia Quality of Life Scale-39 were administered pre- and post-treatment to assess for the treatment-related change.

Outcomes & Results: The participant responded well to MIT, completing the elementary level in 25 sessions and progressing through the intermediate level until the end of the treatment period at session 30. Performance on the ADP suggested decreased aphasia severity characterised by improved auditory comprehension, repetition, average phrase length and elicited gestures. Functional communication was slightly improved, whereas quality of life did not change. It was reported by the spouse, caregiver and clinician that the participant began using several novel phrases in appropriate context over the course of the treatment.

Conclusions: The MIT may be a valid treatment of global aphasia following right hemisphere stroke, providing more options to practising clinicians working with this population. It is likely that the criteria ruling out those with impaired auditory comprehension and those with right hemisphere lesions, regardless of lesion location, are too restrictive. Most likely, good and poor candidates for MIT can better be identified using intrahemispheric lesion location information, rather than interhemispheric.     

Mixed transcortical aphasia: clinical features and neuroanatomical correlates. A possible role of the right hemisphere

This paper reports the clinical features of 2 patients affected by mixed transcortical aphasia. Both of them had extensive damage of the left hemisphere. Cerebral blood flow measurement showed a marked decrease in left-hemisphere flow. In particular, speech areas were found to be morphologically and functionally damaged. The present findings, together with a critical review of the literature, served as a starting point for a discussion of linguistic features, diagnostic criteria and classical neuroanatomical interpretation of mixed transcortical aphasia. The possible contribution of the right hemisphere in determining this aphasic syndrome is suggested.     

The role of the right hemisphere in contextual inference

The present report describes two experiments involving dichotic presentation of sentences which have been electronically altered to render all verbal content indecipherable while leaving the melodic structure of the sentences intact. In both experiments, right-handed subjects produced a significant left ear advantage in identifying the situational context portrayed by the sentences. Left-handers produced no significant ear differences. The left ear advantage on this task was unrelated to the direction or magnitude of subject's ear advantage on a standard CV dichotic task.     

Aphasia from the wrong (right) hemisphere: Questions for crossed aphasia

Abstract

In aphasia as in so many other fields of study it is the exception to the rule that points the way to new theory. Just when we think we have a handle on the problem of language and brain organization, some unusual disorder comes along and forces us to re-examine the simple explanations we have forced on the data.     

Contrasting opinions on the role of the right hemisphere in the recovery of language. A critical survey

Background: The role of the right hemisphere (RH) in the recovery of language is quite controversial.

Aims: The aim of the present survey consisted in taking into account three main models advanced to explain the reconstitution of language systems: (1) the “perilesional hypothesis,” which maintains that language recovery is mainly subsumed by left hemisphere (LH) tissue adjacent to the lesion; (2) the “right hemisphere hypothesis,” which assumes that restitution of language entails an increased participation of the RH; and (3) the “disinhibition hypothesis,” which maintains that recovery is facilitated by disruption of inhibitions exerted by RH regions over LH language areas.

Methods & Procedures: The prognostic factors in poststroke aphasia are discussed first, focusing attention on factors that could subsume an increased participation of the RH to the recovery of language. Then results obtained with techniques of noninvasive brain stimulations of the RH are taken critically into account.

Outcomes & Results: As for the prognostic factors, the following points are stressed: (1) the anatomical extension of the LH lesion plays an important role both on the degree and on the path of recovery; (2) the RH structures involved in the recovery of language are generally mirror structures of the damaged LH areas; and (3) the time elapsed since the onset of aphasia influences the contribution that contralateral and ipsilesional areas give to the recovery of language. As for results obtained with techniques of noninvasive brain stimulations of the RH, this point remains controversial, because most authors support the “disinhibition hypothesis,” but theoretical and factual reasons suggest caution in the interpretation of these results.

Conclusions: Since the meaning of the RH activations and of results obtained with techniques of noninvasive brain stimulations remain controversial, some tentative recommendations to clarify these issues are advanced.     

Crossed aphasia in a patient with congenital lesion in the right hemisphere

Abstract

A phonologically based treatment was implemented to train oral picture naming in four aphasic subjects with severe word-retrieval deficits. An initial assessment based on current cognitive neuropsychological models of naming indicated different levels of phonological and/or semantic deficits underlying naming failure across the subjects. Using a single-subject multiple baseline design across behaviours and subjects, the effects of treatment were evaluated by daily probing of both trained and untrained items across lexical tasks: oral naming, oral reading, and written naming. Results indicated successful acquisition of trained naming targets for the four subjects, and varied patterns of response generalization to naming of untrained phonologically and semantically related pictures, and to oral reading and written naming for the same words. Baseline levels of oral reading performance were noted to predict success in oral naming treatment. Differences in generalization patterns across tasks are discussed with regard to the varying functional levels of breakdown noted across subjects. This investigation demonstrates the utility of cognitive models in guiding the development of appropriate treatment strategies and generalization measures, and the importance of incorporating single-subject experimental designs in documenting changes associated with treatment.     

The role of the unaffected hemisphere in motor recovery after stroke

The contribution of the ipsilateral (nonaffected) hemisphere to recovery of motor function after stroke is controversial. Under the assumption that functionally relevant areas within the ipsilateral motor system should be tightly coupled to the demand we used fMRI and acoustically paced movements of the right index finger at six different frequencies to define the role of these regions for recovery after stroke. Eight well‐recovered patients with a chronic striatocapsular infarction of the left hemisphere were compared with eight age‐matched participants. As expected the hemodynamic response increased linearly with the frequency of the finger movements at the level of the left supplementary motor cortex (SMA) and the left primary sensorimotor cortex (SMC) in both groups. In contrast, a linear increase of the hemodynamic response with higher tapping frequencies in the right premotor cortex (PMC) and the right SMC was only seen in the patient group. These results support the model of an enhanced bihemispheric recruitment of preexisting motor representations in patients after subcortical stroke. Since all patients had excellent motor recovery contralesional SMC activation appears to be efficient and resembles the widespread, bilateral activation observed in healthy participants performing complex movements, instead of reflecting maladaptive plasticity. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

Differences in recovery from constructional apraxia after right and left hemisphere stroke

Abstract

Previous comparisons of constructional apraxia after right and left hemisphere damage have not investigated the influence of time since onset. This paper reports some preliminary findings from stroke patients in a physical rehabilitation trial. Fifty-five patients with right hemisphere damage and 65 with left hemisphere damage were assessed on the WAIS-R Block Design test at 1 month and 6 months post stroke. The groups were similar at 1 month but the left hemisphere group showed better average recovery by 6 months. There was great variability in amount of recovery within the left hemisphere group, suggesting individual differences in initial reasons for failing Block Design, and corresponding differences in the recovery process. Compensation by the right hemisphere is discussed as one possible process. Future detailed longitudinal studies may be useful in contrasting the cognitive deficits which underlie constructional apraxia after right-sided and left-sided lesions, and would provide evidence on mechanisms of recovery and adaptation.     

The role of the right hemisphere in processing negative sentences in context

Given a pattern consisting of x1, x2,..., xn similar elements and y1, which is perceived as different from the former, it is more plausible to assert that y is not x rather than to assert that x is not y (Wason, J. verb. Learn verb. Behav. 4, 7-11, 1965). In order to appreciate such a difference, the entire set has to be considered. Right-hemisphere brain-damaged patients were submitted to a series of visually presented patterns, each pattern consisting of seven similar items and one dissimilar item. Their task was to complete a statement referring to a single element of each pattern. Statements were either simple affirmative or negative sentences. Errors and reaction times were recorded. Patients with a right-hemisphere injury were found to be insensitive to the plausible-implausible dimension in completing negative sentences. It is hypothesized that right-hemisphere brain-damaged patients are less adequate in this task because they are less capable in putting each element into the visual context.     

The role of the right hemisphere in the aetiology of the depressive disorders

Many differences between the hemispheres have been observed, from the gross anatomical level to differences in dendritic structure or neurotransmitter distribution. Analytic reasoning and language functions such as grammar and vocabulary are often lateralized to the left hemisphere of the brain. The right cerebral hemisphere plays a special role in tasks involving the direction of spatial attention, recognition of faces, perception, possibly generation of affect and affective prosody. Depression is associated with many different cognitive impairments e.g. in the domains of working memory and executive functions as well as interpersonal and social cognition problems. Little is known about the relationship between cognitive and affective deficits in depression. Researchers have hypothesised that the laterality of brain damage may facilitate the expression of emotional or affective disturbances. The aim of the study is to describe the role of the right hemisphere in the aetiology of depressive disorders.     

Metaphors and verbal creativity: The role of the right hemisphere

Ample research suggests that the right cerebral hemisphere plays a central role in verbal creativity as well as in novel metaphor comprehension. The aim of the present study was to directly examine the relation between verbal creativity and right hemisphere involvement during novel metaphor comprehension. Thus 30 healthy adults were asked to fill in the Hebrew version of the Remote Association Test to assess their level of creativity. In addition, reaction times and error rates were measured while these participants performed a semantic judgement task on two word expressions presented in a divided visual field paradigm. The word pairs comprised four types of semantic relations: novel metaphors, conventional metaphors, literal word pairs, and meaningless word pairs. Correlations were conducted to assess the relation between level of creativity and processing of the four pair types in the two cerebral hemispheres. The main finding was of a significant negative correlation between degree of creativity and reaction times to novel metaphor processing in the right hemisphere, thus supporting the involvement of this cerebral hemisphere in both tasks. Results are discussed in light of linguistic theories and recent neuroscientific evidence regarding relative hemispheric involvement during semantic processing.     

Metaphors and verbal creativity: The role of the right hemisphere

Ample research suggests that the right cerebral hemisphere plays a central role in verbal creativity as well as in novel metaphor comprehension. The aim of the present study was to directly examine the relation between verbal creativity and right hemisphere involvement during novel metaphor comprehension. Thus 30 healthy adults were asked to fill in the Hebrew version of the Remote Association Test to assess their level of creativity. In addition, reaction times and error rates were measured while these participants performed a semantic judgement task on two word expressions presented in a divided visual field paradigm. The word pairs comprised four types of semantic relations: novel metaphors, conventional metaphors, literal word pairs, and meaningless word pairs. Correlations were conducted to assess the relation between level of creativity and processing of the four pair types in the two cerebral hemispheres. The main finding was of a significant negative correlation between degree of creativity and reaction times to novel metaphor processing in the right hemisphere, thus supporting the involvement of this cerebral hemisphere in both tasks. Results are discussed in light of linguistic theories and recent neuroscientific evidence regarding relative hemispheric involvement during semantic processing.