Neuroimaging research in aphasia rehabilitation is on the rise because of its potential for explaining the mechanisms that underlie language recovery and the conviction that brain-imaging techniques will lead to the development of more effective treatments. Brain imaging may one day guide us in determining the optimal extent and timing for aphasia treatment as well as which treatment approaches work best for which patients.
Measuring Treatment Results
Functional magnetic resonance imaging (fMRI) is being used to investigate the role of extended practice—or overlearning—in maintaining the effects of treatment over the long term. Prior to treatment, patients receive an fMRI scan and are subsequently trained to 90%–100% accuracy in various language rehabilitation treatment programs. One study used a reorganization approach to remediate impaired reading in which words that the patient read poorly were paired with phonologically related words that the patient read well, a treatment that has been shown to be effective behaviorally (Friedman, Sample, & Lott, 2002). Following treatment, a second fMRI scan was obtained. During the next phase of the study, treatment continued for some of the trained items, but not for others. At the end of this "overlearning" phase, a third scan was obtained.
Preliminary results suggest that following successful training, neural activation shifts toward the right hemisphere of the brain. However, following overlearning, activation shifts back to predominately left hemisphere, perilesional regions (Kurland et al., 2007). Heiss et al. (1999) suggest that right-hemisphere processing is an inefficient alternate processing route, and that optimal recovery occurs when left-hemisphere perilesional areas take over processing. Our early research results suggest that not only does overlearning facilitate a shift back to left-hemisphere processing, but also that this shift results in better maintenance.
Neuroimaging research may also help to determine the optimal timing and extent of rehabilitation with individual patients. In the overlearning study described above, a switch from right-hemisphere processing back to left-hemisphere processing might indicate sufficient overlearning. However, behavioral data cannot reveal a change in processing while items are being learned beyond criterion, as the patient is already performing at the ceiling level.
So how does one know, then, that the effects of overlearning have been obtained? Functional MRI may play a role: failure to see a shift in brain activation may indicate that more practice is required, while a shift in activation would suggest that continued treatment is no longer necessary.
Other Treatment Applications
Other applications of fMRI to enhance treatment are being explored. Consider a treatment in which generalization to untrained items is not demonstrated behaviorally. If fMRI reveals a shift in activation for untrained as well as trained words, then there might be evidence that generalization has occurred but its effects have not yet risen above an observable behavioral threshold. In this case, a clinician might be justified in continuing treatment despite a lack of recent progress. It also might be possible to use neuroimaging to predict which patients will succeed with a given treatment. If a treatment results in shifting brain activation to a particular area, then it might be predicted that a patient with additional lesions in that area will not be a good candidate for that treatment.
Because of the complex nature of conducting fMRI research, interdisciplinary collaboration is essential. Imaging experts are required to conduct and analyze fMRI scans, researchers experienced in conducting cognitive studies are needed to design theoretically motivated and well-controlled experiments, and clinicians are crucial for identifying appropriate patients and developing important functional questions. Speech-language pathologists can become involved with fMRI research by collaborating with an established group that has access to fMRI and the requisite expertise.
Currently, fMRI is costly and its practical benefits for individual patients are envisioned but not yet proven. More research is needed, but clearly fMRI is yielding information of great clinical significance. By building upon behavioral findings, fMRI advances our understanding of the underlying mechanisms of rehabilitation and recovery of aphasia.