Brain and Cognition 42, 60–63 (2000)

doi:10.1006/brcg.1999.1162, available online at http://www.idealibrary.com on

Imaging Aphasia: The Coming Paradigm Shift

Pooja Khatri and Daniel B. Hier

University of Illinois

Dating back to 1861, when Paul Broca correlated Leborgne’s left hemi-sphere lesion with his aphasia and right-sided hemiplegia, the dominantmethod in aphasia research has been clinical–anatomical correlation. Withthe advent of PET, followed by SPECT, and finally fMRI, will come a para-digm shift. Instead of correlating brain lesions with aphasic symptoms, wecan now correlate brain function with language performance. Instead of ask-ing, ‘‘What is injured?’’ we can now ask, ‘‘What is working?’’

Functional imaging can address a variety of questions including the locusof activation of a given brain function, the relative responsiveness amongregions involved in the same function, and connecting pathways betweenregions. For instance, Raichle et al. (1997) showed an unexpected activationof the right cerebellum in practice-related learning of verb generation in nor-mal subjects. In addition, Benson et al. (1999) have shown that verb-genera-tion tasks, in contrast with naming and reading tasks, provide remarkablyreliable activation of the dominant hemisphere. New patterns of connectivityhave been suggested by Weiller et al. (1995), who showed that despite com-plete destruction of Wernicke’s area, increased activation in Broca’s area isseen on fMRI during word repetition.

Aphasia occurs in eighty thousand new people each year. Prognostic indi-cators for this devastating condition are needed. Currently, the single mostimportant predictor of long-term outcome is initial aphasia severity, whichlacks the power to predict individual outcome. Another central goal is tounderstand the mechanisms of recovery. Theories such as compensation, re-dundancy, diaschisis, latent pathways, and restoration provide a theoreticalframework for considering how recovery might occur. Empirical data isneeded to know how recovery does occur. Eventually, a better understandingof recovery will lead to more effective clinical interventions. Several intri-

Address correspondence and reprint requests to Pooja Khatri or Daniel B. Hier, Departmentof Neurology, University of Illinois, 912 S. Wood Street, Chicago IL 60612. E-mail: neuro@uic.edu.

600278-2626/00 $35.00Copyright 2000 by Academic PressAll rights of reproduction in any form reserved.

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guing questions must be answered. What is the role of the right hemisphere?How does reorganization of the left hemisphere influence recovery? Do indi-vidual differences in organization of language influence recovery from apha-sia? And how may therapy and retraining remap language in the brain afteraphasia?

The role of the right hemisphere in language function and recovery re-mains controversial. Weiller et al. (1995) have used functional imaging toshow that the right hemisphere may play a crucial role in effective recoveryfrom aphasia. They studied six patients with complete destruction of Wer-nicke’s area who subsequently recovered from Wernicke’s aphasia. Com-pared to controls, these recovered aphasics showed increased activation inright hemisphere areas homotopic to left hemisphere language areas. In addi-tion, they found increased left frontal cortex activation, including Broca’sarea, during a verb generation task. Similarly, Thulborn et al. (1999) fol-lowed the temporal course of two recovering aphasics with fMRI. They dem-onstrated progressive right hemisphere activation during silent sentence read-ing tasks when compared to controls.

Other studies have suggested that recovery from aphasia depends on thesparing of left hemisphere language cortex or reactivation of language areasin the left hemisphere. Karbe et al. (1995) studied twenty-two aphasic pa-tients with a variety of infarcts. They found that the best predictor of two-year outcome after Wernicke’s or Broca’s aphasia was early activation ofleft Wernicke’s or Broca’s area, respectively. In their study, right hemisphereactivation showed no correlation with recovery. Furthermore, some studiesshow that right hemisphere activation by language tasks after aphasia mayactually predict poor recovery. For example, Heiss et al. (1999) dividedtwenty-two patients by left hemisphere infarcts into subcortical, frontal, andtemporal groups, irrespective of aphasia type and severity. They demon-strated that a shift from right hemisphere to left hemisphere activation bylanguage tasks corresponded with better recovery both within and betweengroups, with the best recovery corresponding to preserved and reactivatedleft temporal regions. They hypothesize ‘‘a hierarchy of strategies for recov-ery’’ with the preferred strategy being utilization of previous language zonesin the left hemisphere.

Synthesis of these studies into a cohesive theory of how recovery fromaphasia occurs is difficult. It is complicated by variations in number of pa-tients studied, locations and sizes of infarcts, types of aphasia, aphasia mea-surement, imaging activation tasks, time course of the studies, imaging anal-ysis methods, and research designs. Specifically, why has right hemisphereactivation by language been shown to correlate with good recovery fromaphasia in some studies, and poor recovery in others? Closer examinationof Weiller et al.’s study (1995) yields two speculative explanations. First,perilesional areas that would be unique to certain individuals and not appar-ent with group averaging were not assessed. Second, increased left hemi-

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sphere activation was present in these patients, possibly accounting for someof the recovery noted. In the study by Thulborn et al., the degree to which thetwo patients recovered is not known, as they were not assessed by objectivemeasures. Variability in activation tasks alone cannot explain these differ-ences, as conflicting results are seen between groups using the same tasks(Weiller, 1995; Wharburton, 1999). Thus, while this issue requires furtherstudy, the evidence appears to favor the dominant hemisphere language areasas the source of most recovery from aphasia. However, individual exceptionsmay occur. Functional brain imaging may help us understand whether indi-vidual differences explain differences in recovery from aphasia.

Functional brain imaging also gives us an important tool to study the effec-tiveness of retraining and rehabilitation of aphasia. This may give more infor-mation about the recovery process generally as well. Belin et al. (1996) stud-ied seven nonfluent aphasics with left hemisphere global hypoperfusion whohad an absence of recovery despite standard speech therapies. These patientswere trained with melodic intonation therapy (MIT), a modality of aphasiatherapy, for two years and subsequently imaged by PET. Increased homo-topic right hemisphere activation was visualized without MIT word repeti-tion, while the same patient showed increased left hemisphere language areaactivation with MIT word repetition. The study by Belin et al. suggests thatright hemisphere activation patterns may not be related to the recovery pro-cess. Instead they may represent the persistence of aphasia, a significant shiftin the understanding of right hemisphere activation if supported by furtherstudies.

In conclusion, functional imaging allows us to address previously unan-swerable questions including the role of the right hemisphere in recoveryfrom aphasia, how the left hemisphere reorganizes itself for language afteraphasia, how individual differences in organization for language contributeto recovery from aphasia, and how rehabilitation from aphasia alters brainorganization for language. As answers to these questions lead to new anddifferent understandings of the brain, the paradigm shift is on the way.

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Belin, P., Van Eeckhout, P., Zilbovicius, M., Remy, P., Francois, C., Guillaume, S., Chain,F., Rancurel, G., & Samson, Y. 1996. Recovery from nonfluent aphasia after melodicintonation therapy: A PET study. Neurology, 47, 1504–1511.

Benson, R. R., Fitzgerald, D. B., LeSueur, L. L., Kennedy, D. N., Kwong, K. K., Buchbinder,B. R., Davis T. L., Weisskoff, R. M., Talavage, T. M., Logan, W. J., Cosgrove, G. R.,Belliveau, J. W., & Rosen, B. R. 1999. Language dominance determined by whole brainfunctional MRI in patients with brain lesions. Neurology, 52, 798–809.

Heiss, W-D., Kessler, J., Thiel, A., Ghaemi, M., & Karbe, H. 1999. Differential capacity ofleft and right hemispheric areas for compensation of poststroke aphasia. Annals of Neurol-ogy, 45, 430–438.

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