P108. The effect of task effort on recovery-related brain activity following motor stroke assessed with FMRI and EEG. Issue 8 (August 2015) - Bönstrup, M.
Abstract Introduction Spontaneous recovery of motor deficits after stroke evolve at a rather unpredictable fashion regarding the time and extend of skill reacquisition (Langhorne et al., Lancet, 2011). Previous longitudinal studies investigating brain activity during recovery from hand motor deficits point to an early overactivation of the motor network with a decrease back to near normal patterns later after stroke (Rehme et al., Neuroimage, 2012). Since patients regain force and skill during recovery, changes in neural activation over time could be explained by a decreased relative task effort over time. Such a behavioral bias could affect neuroimaging findings and their interpretation in regard to recovery, a question not or not sufficiently accounted for in previous studies. The aim of the present study was to systematically investigate the influence of task effort on recovery-related brain activation. We addressed the question whether keeping either task effort or task output constant leads to differing patterns of recovery-related brain activation over time within a "constant output-constant effort" design. We speculated that due to the recovery-related increase in manual power, the two experimental conditions show different evolutions of brain activity patterns with constant output reflecting stronger changes over time. Since electroencephalography and functional magnetic resonance imaging measure different aspects of brain activation, we used a multimodal approach. Methods We assessed brain activity with functional magnetic resonance imaging (FMRI, blood oxygenation level dependent signal (BOLD)) and EEG based task-related spectral-power within lower alpha, upper alpha, beta band, in a longitudinal design covering the acute (3–5 d post stroke), subacute (30 days) and early chronic (90 days) phase after an ischemic infarction causing a hand motor deficit. At every time point, patients (n = 12 (EEG)/8 (FMRI), m = 6, age 66.67 ± 9.03 (mean ± std), 4 left hemispheric lesions) performed whole hand grips with both 5 kg constant output and 20% of the current individual maximal force (constant effort). Results Patients showed significant recovery over time (increase in grip force over time, p < 0.001). In parallel, we found a significant reduction in task-related brain activity during recovery (p < 0.01). Relative task effort had no significant impact on the evolution of task-related brain activation over time (TASK × TIME, n.s.). This proved to be equally applicable to FMRI and EEG data (TASK × TIME × METHOD, n.s.; TASK × METHOD n.s.; TIME × METHOD, n.s.). Conclusion This longitudinal study demonstrates in mildly affected patients that task-related brain activity significantly decreases over time as suggested previously. The main finding was that the dynamic change of brain activation over time did not relate to the effort necessary to perform the task at each measurement time point. In detail, this shows that the task effort had no significant effect on the slope of brain activity decrease in the course of recovery. These data suggest that the decline of motor task-related brain activity during recovery is largely reflecting adaptive processes in the course of neuronal reorganization and is not influenced significantly by behavioral/cognitive differences, such as effort, over time. Using multimodal imaging, two independent measures of neural activity (BOLD, EEG power) support this finding, mutually validating methodological assessment of brain activation and augmenting the explanatory power.