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DOI: 10.1055/s-0031-1272699
Effective connectivity within the cortical motor system predicts behavioural response to theta-burst stimulation in stroke patients
Introduction: Previous studies showed that repetitive transcranial magnetic stimulation, especially theta-burst stimulation (TBS), may enhance neural plasticity. This renders TBS an interesting therapeutic tool for treatment of stroke-induced motor deficits. Improvements have been demonstrated but effects remain highly variable across individuals and some patients may even show deterioration of motor performance. Hence, we aimed to identify predictors for the behavioural response to TBS, which appears essential for its implementation in neurorehabilitation.
Methods: 13 chronic stroke patients with motor hand deficits due to a stroke in the middle cerebral artery territory and 12 age-matched healthy control subjects were scanned with fMRI while performing visually-paced fist closures. Region-of-interest (ROI) analyses and dynamic causal modelling (DCM) were performed using SPM8. On two different days, patients received: (i) intermittent TBS (iTBS, excitatory) over the primary motor cortex (M1) of the affected hemisphere, and (ii) control TBS over the midsagittal parietooccipital cortex. A motor improvement score was calculated based on the Jebsen-Taylor hand function test, indexfinger tapping, and grip force measurements, and correlated with fMRI signal in ROIs and DCM coupling parameters.
Results: iTBS was not superior to control TBS across the whole group of patients. Correlation analyses revealed that especially patients with less pathological activity in contralesional M1 and SMA (supplementary motor area), and ventral premotor cortex bilaterally improved after iTBS.
Fig.1: Correlations between improvement of the stroke affected hand after iTBS and fMRI BOLD signal
Connectivity analysis showed that the response to iTBS was predicted by the integrity of motor network connectivity: The higher the coupling between ipsilesional SMA and M1 and the more effective interhemispheric inhibition of the contralesional M1, the better the response to iTBS.
Fig.2: Correlations between improvement of the stroke affected hand after iTBS and effective connectivity
Conclusion: Our data suggest that fMRI signal of key motor areas as well as network interactions between areas constitute promising predictors for response to iTBS. Especially in patients where the connectivity pattern of the affected motor network resembled physiological network connectivity patterns (i.e. preserved inhibition of the unaffected hemisphere and supportive role of the SMA of the affected hemisphere), beneficial effects of iTBS over the affected hemisphere could be observed: In contrast, patients with severely disturbed motor networks did not respond to iTBS or even deteriorated.