| Summary: | Introduction:
The neural mechanisms that support aphasia recovery are not yet fully understood. A previous, longitudinal fMRI study of language recovery in stoke patients using auditory comprehension task found that aphasia recovery is characterized by: little activation (in either hemisphere) during the acute phase; a large increase in activation in the bilateral network; and a shift of language back to the left hemispheric in the chronic phase (Saur et al., 2006). However, it is unclear whether other language tasks would show a similar time course in recovery and whether there would be individual differences in the recovery pattern. Our aim in the current study was to investigate the neural correlates of recovery of naming from the acute to chronic stage.
Methods:
6 right-handed participants with acute ischemic left hemisphere stroke (mean age: 53.1 years) and 2 normal controls (mean age: 52.5 years) with no history of neurological disorder were enrolled in this study. All stroke patients had clinical scans within 24 hours of symptom onset. Participants received detailed language testing and research scans (MPRAGE and BOLD) at 4 time points (acute, 2-5 weeks, 4-7 months, and 11-13 months). The fMRI task was a cued picture-naming task (Holland et al., 2011). Each picture was presented concurrently with an auditory cue, which was either: (i) a whole word (ii) an initial phoneme or (iii) an unintelligible auditory noise. The control condition consisted of viewing scrambled pictures. Trials were presented in short blocks of six pictures, separated by the control condition of 7 s. fMRI data were preprocessed and analyzed in FSL (Smith et al., 2004; Jenkinson et al., 2012). Contrast compared picture naming (initial+word cues) to control condition.
Results:
Successful overt picture naming in the normal controls involved a bilateral fronto-temporal, parietal and occipital network at all time points. All patients showed bilateral activation in the temporo-parietal and/or frontal regions at the acute time point. Follow up scans revealed different recovery patterns for the patients. For example, follow up scanning for P3 did not show any significant change from the acute stage, although her naming ability had markedly improved. P4’s naming ability continued to improve at the follow up time points with a corresponding increase in left hemisphere activation at the follow up time points (see Figure 1).
Conclusion:
Our preliminary data suggests that recovery of naming is dynamic and may have different time courses in different individuals. Further, brain reorganization during language recovery may not proceed in three phases as proposed by Saur and colleagues. This finding is in line with the recent work from our lab, which examined recovery of language within the first two months after a stroke (Jarso et al., 2014). To further understand the processes involved in naming recovery, we are analyzing DTI and resting state fMRI data. It is hoped that the results from the multimodality imaging data will serve as the basis for targeted brain-based interventions for aphasia, which require an understanding of the anatomy of language networks, as well as the extent and timing of how these networks reorganize after injury.
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