Elsevier

Brain and Language

Volume 82, Issue 2, August 2002, Pages 206-222
Brain and Language

The contribution of the right cerebral hemisphere to the recovery from aphasia: a single longitudinal case study

https://doi.org/10.1016/S0093-934X(02)00017-2Get rights and content

Abstract

We examined the role of the right cerebral hemisphere in the recovery from aphasia of HJ, a 50-year-old right-handed and unilingual man who suffered from severe aphasia caused by an extensive left hemisphere (LH) lesion. He was followed-up over 10 months at 4-month intervals, with a lateralized lexical decision task (LDT), an attentional task, and a language battery. Testing started when HJ was 2 months poststroke. In the LDT, words were presented to central vision or lateralized to the left or right visual hemifield. At each test period, we examined the effect of the degree of imageability (high vs. low), and the grammatical class (noun vs. verb) of the targets on HJ's response times and error rates, with left visual field, right visual field, and central vision presentations. The results of the experiment showed that the pattern obtained with the LDT could not be accounted for by fluctuations in attention. There was an interaction of grammatical class with degree of imageability with left visual field displays only. The right hemisphere (RH) was faster with high-imageability words than with low-imageability words, regardless of their grammatical class. There was also an overall RH advantage on response times at 2 and 6 months after onset. This RH predominance coincided with a major recovery of language comprehension and the observation of semantic paralexias, while no major change in language expression was observed at that point. Ten months after onset, the pattern of lateralization changed, and response times for the LDT with either presentation site were equivalent. This LH improvement coincided with some recovery of language expression at the single-word level. The results of this study suggest that, in cases of severe aphasia caused by extensive LH lesions, the RH may play an important role in the recovery process. Furthermore, these results show that the contribution of the two cerebral hemispheres to recovery may vary overtime and affect specific aspects of language.

Introduction

Aphasia caused by left hemisphere (LH) damage in right-handed subjects is generally followed by some degree of language recovery. It has proven difficult to identify the mechanisms underlying this recovery. Determining the neural substrate for recovery and its relationship with specific aspects of word processing may provide cues for language intervention. This paper reports on a literature review of the issue and then a study of language recovery in an aphasic patient.

It is generally accepted that the brain may use either of two ways to cope with language impairment following cerebral damage: the recovery of the language-relevant areas in the LH or the reorganization of the language-relevant network by recruiting supplementary brain areas in the LH or right hemisphere (RH). The former hypothesis was first proposed by Wernicke (1874), while the latter was advanced by Broca (1865), who raised the theoretical question of why a patient who became aphemic following a lesion in the left third frontal convolution could not learn to talk with his RH.

More than a century ago, Gowers (1887) provided empirical evidence of the role played by the RH in the recovery from aphasia, when he reported the case of a right-handed subject who became aphasic following an LH lesion, recovered language as time elapsed after his aphasia, and then lost this recovered language following a second lesion in the RH. Accordingly, Gowers proposed that recovery from aphasia could result from RH takeover of language aspects previously committed to the damaged regions of the LH. Since then, much clinical and experimental evidence has indicated that the RH may sustain a recovery from aphasia, particularly in cases of severe left cerebral damage.

Among clinical investigations, a series of studies similar to that of Gowers (1887) have reported cases of aphasic subjects who recovered some language functions and then lost the recovered language following a new lesion in the RH. These findings have consistently been interpreted as evidence for RH takeover following aphasia (Basso et al., 1989, Cambier et al., 1983, Henschen, 1926, Levine and Mohr, 1979, Moutier, 1908, Nielsen, 1946, Nielsen and Raney, 1939). In spite of the interest of such clinical studies, one should interpret their observations with regard to the RH's role in recovery from aphasia with caution. The pattern described in these studies could very well result from diaschisis (Von Monakow, 1914), a neurophysiological phenomenon that causes a disruption of brain activity in cerebral regions that are distant from the damaged areas. Hence, the deterioration of a previously improved language function after a new RH lesion could result from the effect exerted by the latter upon the homologous regions in the LH, rather than from the destruction of newly acquired RH language functions after left brain damage. Given that the earlier studies reported changes in the aphasic condition in the short term following an RH lesion, the possibility that diaschisis may be responsible for the loss of recovered language cannot be excluded.

In a different type of clinical report, Cummings, Benson, Walsh, and Levine (1977) described the recovery of auditory comprehension and automatic speech in an individual who had become globally aphasic following an embolic infarction in the distribution of the left middle cerebral artery. Computerized tomography (CT) showed the total destruction of the LH language areas. From this, the authors concluded that the RH necessarily sustained the recovered language. As reported by Cummings et al., it is likely that the RH plays an important role in language recovery when aphasia results from the massive destruction of the LH; however, this may not be so when damage to the LH is not extensive. Residual portions of the LH may be responsible for language recovery in such cases.

Congruently, neuroimaging and neurophysiological studies have found that there is an inverse correlation between the size of the LH lesion and the degree of language recovery (Demeurisse et al., 1985, Heiss et al., 1993). This observation supports the claim that the residual portions of the LH are crucial for the recovery from aphasia. For instance, Heiss et al. (1993) used positron emission tomography (PET) to study a group of acute aphasic subjects. They found that the resting metabolism of the LH outside the area of infarct was the single most important predictor of language performance on a word repetition task 4 months after stroke. Demeurisse and Capon (1987) conducted a longitudinal study in which they examined the correlation between clinical recovery and the changes in regional cerebral blood flow which signal cerebral activation. The authors found that the recovery of oral expression was positively correlated with the number of activated LH regions 3 weeks after the stroke. In contrast to the previous studies, however, bilateral participation in the recovery from aphasia was claimed by Weiller et al. (1995), who studied a group of recovering aphasics using PET and functional magnetic resonance imaging (fMRI). Over time, these authors found an increased activation in the left frontal language areas and right perisylvian areas of their subjects, during continuous silent lexical search and silent repetition of verbs. According to the authors, these findings indicate that both cerebral hemispheres contribute to the recovery from aphasia. Notwithstanding the interest of this study, given that the authors used a silent task, it is not possible to ascertain the extent to which the aphasic subjects could accomplish the task, and thus the interpretation of the results should be prudent.

Another experimental paradigm that has been used to examine the performance of the two cerebral hemispheres during the recovery from aphasia involves divided auditory or visual field presentations. Aphasic subjects given lateralized tasks have shown a left-ear advantage on auditory tasks (Castro-Caldas and Silveira Bothelo, 1980, Niccum, 1986), and a left visual field advantage on visual tasks (Schweiger & Zaidel, 1989). The left-side advantage has been taken as evidence of an RH takeover of language processing following aphasia. However, a left-side advantage may also have resulted from a shift of attentional resources to the left hemifield as a consequence of the LH lesion (Kinsbourne, 1970). The above observations therefore do provide definitive evidence of an RH takeover specific to language processing.

In summary, the literature is not unanimous with regard to the role of the RH in the recovery from aphasia. Neurophysiological and neuroimaging studies (Demeurisse & Capon, 1985; Heiss et al., 1993) suggest that it is the preservation of the LH that determines recovery, whereas clinical evidence (Basso et al., 1989, Cambier et al., 1983, Henschen, 1926, Levine and Mohr, 1979, Moutier, 1908, Nielsen, 1946, Nielsen and Raney, 1939) and lateralization studies (Castro-Caldas and Silveira Bothelo, 1980, Niccum, 1986, Schweiger and Zaidel, 1989) suggest that the RH may play a role in the recovery from aphasia.

Evidence from studies of neurologically intact subjects indicates that their RH is sensitive to lexical semantic information. Thus, divided field studies with normal subjects have found that the habitual right visual field advantage–LH superiority (Rvf-LH) attenuates or even disappears with visual presentations of concrete and/or high-imageability words (Day, 1977, Day, 1979, Ellis and Shepherd, 1974, Hines, 1976, Mannhaupt, 1983, Young and Ellis, 1985). More specifically, Day (1979) found no difference between response times to left and right visual field presentations of high-imageability nouns, but found an Rvf-LH advantage with low-imagery nouns and verbs, regardless of their degree of imageability. The author concluded that the RH can process high-imageability nouns, while low-imageability nouns and verbs are exclusively processed by the LH. Other studies, however, have reported no significant effect of these variables (e.g., Boles, 1983, Eviatar et al., 1990, Howell and Bryden, 1987, Koening et al., 1992, Lambert and Beaumont, 1983, McMullen and Bryden, 1987).

This lack of consistency between studies may result from such methodological issues as the lack of control over lexical frequency. Hence, Nieto, Santacruz, Hernandez, Camacho-Rosales, and Barroso (1999) found an imageability effect with both nouns and verbs, arguing that Day (1979) failed to find an imageability effect with verbs because he did not control for lexical frequency in the verb category. Furthermore, Nieto et al. claim that Eviatar et al. (1990) failed to find a differential effect of grammatical class or imageability across the Rvf-LH and the left visual field-right hemisphere (Lvf-RH) because the set of verbs they used was actually made up of words that are both nouns and verbs. In summary, the results of lateralization studies with normal populations show that imageability, word class, and word frequency should all be taken into consideration and strictly controlled for when examining the role of the RH in the recovery from aphasia.

The purpose of the present study was to examine this very issue. We examined longitudinally the impact of degree of imageability and grammatical class on the lexical decision performance in HJ, a severely aphasic subject who suffered from a large lesion in the LH. HJ was followed at 4-month intervals for a period of 10 months, using a lateralized lexical decision task, an attentional task, and an aphasia test battery. The results of this experiment are discussed with reference to the RH's role in the recovery from aphasia.

Section snippets

Case report

HJ, a 50-year-old right-handed, French-speaking man was admitted in May 1997 for assessment of a right hemiplegia and aphasia. In April 1997, HJ had undergone a coronary bypass, after which he suffered sudden right hemiplegia and aphasia resulting from occlusive CVA. HJ had no history of cerebrovascular disease and no family history of left-handedness. He was French-speaking and had a university degree. A CT scan conducted in May 1997 showed a large infarct in the distribution area of the left

Materials and methods

The experimental protocol made use of three tasks:

  • (a)

    an aphasia test battery, the Montreal–Toulouse Aphasia Battery (Béland & Lecours, 1990), which served to determine HJ's pattern of aphasia;

  • (b)

    a lateralized lexical decision task (LDT), in order to compare HJ's performance on Lvf-RH, Rvf-LH, and central vision presentations of isolated words;

  • (c)

    an attentional task, the nonverbal Stroop Test (NVST; Beauchemin, Arguin, & Desmarais, 1996), which served as an assessment of attentional resources.

Repeated

Montreal–Toulouse Protocol

For each test (T1, T2, and T3), the number of correct responses on each subtest as well as the types of errors committed (i.e., type of paraphasia, type of paralexia) were considered. These results are outlined in Table 1.

There was an improvement in comprehension over time, in both the oral and the written modalities. Specifically, it concerned written word and oral sentence comprehension and was mainly observed between T1 and T2. Oral and written naming were severely impaired at T1, as was

Discussion

The goal of this study was to examine the role of the RH in the recovery from aphasia of HJ, who suffered from a severe aphasic disorder. The results show that HJ's performance on the lateralized LDT was jointly influenced by degree of imageability, presentation site, time elapsed, and grammatical class.

Time elapsed after aphasia contributed to a reduction in the ER with all word types except low-imageability verbs. There was also a reduction in the ER over time for Lvf-RH and Rvf-LH

Conclusion

The results of this experiment show that both cerebral hemispheres participated in HJ's recovery from aphasia. However, the pattern of lateralization with the LDT indicates that the relative contribution of the two cerebral hemispheres varied during the course of recovery. The RH appeared to dominate language processing between 2 and 6 months after aphasia, and this coincided with an improvement in language comprehension, but not in language expression. Furthermore, the RH was particularly

Acknowledgements

The work was made possible by the financial support of Consejo Nacional de Investigatión en Ciencia y Tecnologı́a de la República Argentina (A.I.A.), as well as a group grant (M.A.) and a team grant (A.R.L.) from the FCAR. Martin Arguin is a research fellow under the Fonds de la recherche en santé du Québec. The work was done in partial fulfillment of the requirements for Ana Inés Ansaldo's Ph.D. dissertation.

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