Functional MRI of Language in Aphasia: A Review of the Literature and the Methodological Challenges

Abstract

Animal analogue studies show that damaged adult brains reorganize to accommodate compromised functions. In the human arena, functional magnetic resonance imaging (fMRI) and other functional neuroimaging techniques have been used to study reorganization of language substrates in aphasia. The resulting controversy regarding whether the right or the left hemisphere supports language recovery and treatment progress must be reframed. A more appropriate question is when left-hemisphere mechanisms and when right-hemisphere mechanisms support recovery of language functions. Small lesions generally lead to good recoveries supported by left-hemisphere mechanisms. However, when too much language eloquent cortex is damaged, right-hemisphere structures may provide the better substrate for recovery of language. Some studies suggest that recovery is particularly supported by homologues of damaged left-hemisphere structures. Evidence also suggests that under some circumstances, activity in both the left and right hemispheres can interfere with recovery of function. Further research will be needed to address these issues. However, daunting methodological problems must be managed to maximize the yield of future fMRI research in aphasia, especially in the area of language production. In this review, we cover six challenges for imaging language functions in aphasia with fMRI, with an emphasis on language production: (1) selection of a baseline task, (2) structure of language production trials, (3) mitigation of motion-related artifacts, (4) the use of stimulus onset versus response onset in fMRI analyses, (5) use of trials with correct responses and errors in analyses, and (6) reliability and stability of fMRI images across sessions. However, this list of methodological challenges is not exhaustive. Once methodology is advanced, knowledge from conceptually driven fMRI studies can be used to develop theoretically driven, mechanism-based treatments that will result in more effective therapy and to identify the best patient candidates for specific treatments. While the promise of fMRI in the study of aphasia is great, there is much work to be done before this technique will be a useful clinical tool.

Insights into Adult Postlesional Language Cortical Plasticity Provided by Cerebral Blood Oxygen Level–Dependent Functional MR Imaging

“…This stroke imaging study, 31 in addition to others (Heiss, 5 Cao et al, 32 Heiss et al, 33 Perani et al, 34 and Crosson et al, 35 ), suggests that effective recovery from aphasias is associated predominantly with ipsilateral adaptive changes, with only a secondary contribution from contralateral homologous regions, while poorer recovery of language function is associated with greater right hemispheric than perilesional left hemispheric reorganization. In fact, Heiss 5 suggests that increased activation within the right hemispheric homologous regions may actually be a marker of failed or inadequate recovery attempts stemming from maladaptive plasticity or the loss of normal interhemispheric control within the distributed neural network through impaired transcallosal inhibition.…”

“…Crosson er al, 35 in their review of the literature relating to functional imaging of recovery of language in stroke-induced aphasia, suggest that the size of a left hemispheric infarct may also be a major factor in determining the respective contributions of right hemispheric and left hemispheric mechanisms to overall language reorganization. Specifically, they cited the work of Heiss et al, 33 which suggests that small left hemispheric lesions result in effective perilesional reorganization, while larger lesions destroying larger volumes of eloquent language cortex result in less effective contralesional right hemispheric reorganization.…”

“…Specifically, they cited the work of Heiss et al, 33 which suggests that small left hemispheric lesions result in effective perilesional reorganization, while larger lesions destroying larger volumes of eloquent language cortex result in less effective contralesional right hemispheric reorganization. 35 In addition, Crosson et al 35 raised the possibility that under some circumstances, activation of either the right or left hemisphere may actually interfere with rather than promote recovery of language function. Only a few studies using fMRI to monitor aphasia therapy have been published to date (eg, Wierenga et al, 39 Crosson et al, 40 Meinzer et al, 41 Peck et al, 42 Fridriksson et al, 43 and Vitali et al, 38 ), but unfortunately these studies included only small sample sizes and demonstrated divergent results regarding predominance of left-versus-right hemispheric recruitment as manifestation of posttreatment language plasticity.…”

Dynamics of functional MRI and speech function in patients after resection of frontal and temporal lobe tumors

“…Ранее появление очагов активации в правом по-лушарии у больных с левополушарными инсульта-ми и наличием афазии связывалось исключительно с участием правого полушария в компенсации рече-вых расстройств [2][3][4][5]. Однако нами были обнару-жены очаги активации в правом полушарии у боль-ных без афазии, либо, наоборот, активация в правом полушарии отсутствовала при наличии грубой афа-зии после операции.…”

“…Показано, что, по данным фМРТ, в первые часы после развития инсульта c речевыми нарушениями нехарактерно появление активации гомологичных речевым полям отделов правого полушария мозга [1]. При исследовании больных с помощью фМРТ и позитронно-эмиссионной томографии (ПЭТ) в хро-нической стадии постинсультной афазии выявление активации гомологичных речевым зонам областей правого полушария является типичным [2][3][4][5]. Для активации структур правого полушария у больных с левополушарными инсультами при предъявлении речевых нагрузок требуется время.…”