gms | German Medical Science

Objective: Brain stimulation has the potential to become a valuable intervention for patients with severe upper-limb paresis following brain injury, surgery or stroke. Neuromodulation has been shown to be most effective in inducing neuroplasticity when applied in conjunction with repetitive motor practice. However, we hypothesize that stimulation should be applied depending on the current brain-state in order to maximize stimulation effect. In that sense, cortical β-oscillations play a crucial role in defining movement-associated brain-states. Here we present our results on the relation between the effects of transcranial magnetic stimulation (TMS) and ongoing cortical β-oscillations.

Method: We developed a experimental environment with the opportunity to provide haptic and/or visual feedback of electromyographic (EMG) and electroencephalographic (EEG) activity conditioning subjects to reproducibly activate the central motor system both with and without muscle activation. Concurrently, navigated TMS was applied to the contralateral motor cortex in order to probe motor-evoked potentials (MEP) during different brain-states.

Results: In the condition of central motor system activation with suppressed muscle activity (MI), power of pre-stimulus cortical β-activity correlated inversely with MEP amplitude. Moreover there was a frequency-specific, phase-dependent modulation of MEP amplitude by cortical β-oscillations. At the same time, there was a frequency-specific modulation of MEP amplitudes by muscular β-oscillations phase-locked to cortical β-activity.

Conclusions: The present provides evidence that sensorimotor β-rhythms represent the intrinsic excitability of cortical pyramidal neurons. Hence, ongoing cortical β-oscillations are a promising target for closed-loop stimulation paradigms in order to induce cortical neuroplasticity, e.g. in motor restoration.