Functional MRI of Language in Aphasia: A Review of the Literature and the Methodological Challenges |
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| Authors: | Bruce Crosson Keith McGregor Kaundinya S Gopinath Tim W Conway Michelle Benjamin Yu-Ling Chang Anna Bacon Moore Anastasia M Raymer Richard W Briggs Megan G Sherod Christina E Wierenga Keith D White |
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| Institution: | (1) Department of Veterans Affairs Rehabilitation Research and Development Brain Rehabilitation Research Center at the Malcom Randall VA Medical Center, Gainesville, Florida, USA;(2) University of Florida Department of Clinical and Health Psychology, Gainesville, Florida, USA;(3) University of Florida, Department of Psychology, Gainesville, Florida, USA;(4) McKnight Brain Institute of the University of Florida, Gainesville, Florida, USA;(5) University of Texas Southwestern Medical School Department of Radiology, Dallas, Texas, USA;(6) Aging Veterans with Vision Loss Center, Atlanta VA Medical Center, Atlanta, Georgia, USA;(7) Emory University, Department of Physical Medicine and Rehabilitation, Atlanta, Georgia, USA;(8) Old Dominion University Department of Early Childhood, Speech-Language Pathology, and Special Education, Norfolk, Virginia, USA;(9) University of California, San Diego Department of Psychiatry, San Diego, California, USA |
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| 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. |
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| Keywords: | fMRI Aphasia Rehabilitation Neuroplasticity Language |
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