Cortical and subcortical connectivity during hand movements at different frequencies

Aims: Motor actions result from an interplay of various brain regions engaged in different aspects of movement preparation and execution. Functional imaging studies have shown that increasing the speed of a movement is associated with higher blood oxygen level dependent (BOLD) responses within the contralateral sensorimotor cortex¹. It is, however, not known which areas drive these increases in neural activity. Therefore, we investigated the effective connectivity during paced fist closure at different frequencies to identify the motor regions that are involved in frequency-dependent hand movements. Methods: Twenty healthy subjects were scanned with functional magnetic resonance imaging (fMRI) at 3 Tesla while performing fist closures at three different frequencies (0.75 Hz, 1.5 Hz, and 3.0 Hz). Dynamic causal modelling (DCM) was used to reveal the specific excitatory and inhibitory influences within a bihemispheric network of cortical and subcortical key motor areas consisting of primary motor cortex (M1), supplementary motor area (SMA), premotor cortex (PMC), basal ganglia and cerebellum. Results: The statistical analysis revealed that with higher movement frequencies effective connectivity between the contralateral premotor areas (SMA, PMC) and contralateral (left) M1 significantly increased. Similar effects were observed between the ipsilateral cerebellum and M1. Interestingly, negative influences upon ipsilateral (right) M1 were attenuated with increasing movement frequencies. Conclusion: A more effective coupling between distinct cortical and subcortical motor areas seems to be an important feature of faster hand movements. Such an interpretation is well compatible with the finding that reduced effective connectivity after stroke between SMA/PMC and M1 is associated with stronger motor impairments^2,3. Hence, enhancing coupling among these areas by means of non-invasive brain stimulation might be useful for improving recovery of hand function after stroke.

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