Functional magnetic resonance imaging before and after aphasia therapy - Shifts in hemodynamic time to peak during an overt language task

Background and Purpose - Comparing the temporal characteristics of hemodynamic responses in activated cortical regions of aphasic patients before and after therapy would provide insight into the relationship between improved task performance and changes in blood oxygenation level - dependent ( BOLD) functional MRI ( fMRI) signal. This study investigated differences in the time to peak (TTP) of hemodynamic responses in activated regions of interest (ROIs), before and after therapy, and related them to changes in task performance. Methods - Three aphasic patients and 3 controls overtly generated a single exemplar in response to a category. For the patients, TTP of hemodynamic responses in selected ROIs was compared before and after language therapy. The timing differences between auditory cues and verbal responses were compared with TTP differences between auditory and motor cortices. Results - The selected ROIs were significantly activated in both aphasic patients and controls during overt word generation. In the aphasic patients, both the timing difference from auditory cues to verbal responses and the TTP difference between auditory and motor cortices decreased after rehabilitation, becoming similar to the values found in controls. Conclusions - Findings indicate that ( 1) rehabilitation increased the speed of word-finding processes; ( 2) TTP analysis was sensitive to this functional change and can be used to represent improvement in behavior; and ( 3) it is important to monitor the behavioral performance that might correlate with the temporal pattern of the hemodynamic response.