Initial right hemisphere take-over and subsequent bilateral participation during recovery from aphasia

Background: In 1887, Gowers proposed that supplemental action by the right frontal cortex could sustain language following aphasia. Since then, many studies using a wide variety of experimental paradigms have examined the role of the right hemisphere in the recovery from aphasia. Aims: This study examines the right hemisphere's participation in the recovery from aphasia between four and sixteen months following brain damage. Methods & Procedures: RJ, a young woman with severe Broca's aphasia resulting from a left fronto-temporal hematoma, was followed up at four-month intervals with a divided visual field presentation lexical decision task (LDT). At each time of measurement, we examined her performance with high- and low-imageability nouns and verbs, directed to either cerebral hemisphere and in central vision. A language test was used to examine the pattern of language recovery over time, and a non-verbal version of the Stroop test (NVST) served to follow up changes in attention. The results obtained with the LDT and the NVST were analyzed with ANOVAs; the changes in the pattern of language recovery and the results on the attentional task were also considered in the analysis. Outcomes & Results: There was a left visual field advantage with high-imageability words, regardless of their grammatical class, at four months post stroke. The right hemisphere advantage extended to low-imageability words at eight months after aphasia onset. Concurrently, language comprehension tasks made a significant recovery, whereas language expression tasks recovered only slightly. Furthermore, there was no significant improvement on the attentional task within the same time period. One year after the stroke, RJ's pattern of lateralization changed; there was a marginally significant central vision advantage on word processing, and no significant difference in her performance on lateralized presentations. There was a remarkable recovery on oral expression tasks, and some improvement on the attentional task within the same period. Conclusions: The results of the present study indicate that recovery from aphasia may be sustained by both cerebral hemispheres. The participation of either hemisphere may vary with time elapsed. Our results suggest that high-imageability nouns and verbs may constitute a good target for speech therapy during the first months post stroke, in order to benefit from right hemisphere takeover capacities. Furthermore, low imageability nouns and verbs are candidates for right hemisphere takeover as well, if enough time is allowed. Finally, the results of this study suggest that right hemisphere involvement in language recovery may occur in the absence of a concurrent improvement of attention. In line with previous studies, our results indicate that the recovery of oral expression coincides with the improvement of left hemisphere function. Hence, the fact that language expression started to improve one year after the stroke suggests that recovery from a severe language expression deficit is a long process, and may require long-term follow-up.