AbstractCervical extensor muscle (CEM) fatigue alters upper limb proprioception and impairs the learning of an upper limb-tracking task (Zabihhosseinian et al., 2015). Somatosensory evoked potentials show that cerebellum disinhibition (CBI) is a characteristic response of motor skill learning, which is a process more recently shown to be altered by neck pain (Baarbé et al., 2015). While previous studies demonstrated these responses as changes in sensory processing, the impact on motor cortex output remains unknown. This study aimed to determine whether CEM fatigue alters the CBI response to motor skill acquisition. Sixteen healthy individuals were randomly assigned to either a CEM fatigue or control intervention. Double cone coil transcranial magnetic stimulation (TMS) was applied over the ipsilateral cerebellum 5 ms prior to contralateral stimulation of the primary motor cortex (M1) area supplying the first dorsal interosseous muscle. Cerebellar stimulation levels were delivered to create approximately 50% motor evoked potential inhibition (CBI50), as well as at 5 (CBI50+5) and 10% (CBI50+10) above CBI50. Both groups completed a novel motor tracing task using their right index finger before, immediately after, and 24-hours after experiencing five minutes of neck fatigue or rest. A significant effect of training showed greater disinhibition at CBI50 versus CBI50+10% (P < 0.008), and at CBI50+5% versus CBI50+10% (P < 0.009). Motor training lead to significant cerebellar disinhibition with no impact of CEM fatigue, indicating that the sensory changes reported previously (Zabihhosseinian, 2018) did not lead to the same changes in the cerebellar-M1 pathway.
Acknowledgments: Natural Science and Engineering Research Council of Canada (NSERC), Ontario Graduate Scholarships, and University of Ontario Institute of Technology