The frequency-dependent effects of primary hand motor cortex stimulation on volitional finger movement

We conducted a prospective study in human patients undergoing awake craniotomies to examine whether the effects of cortical stimulation in hand primary motor cortex (M1) can be (1) frequency dependent and (2) inhibitory.

In 11 participants undergoing clinically indicated awake craniotomies, we delivered bursts of 1-333 Hz stimulation during a finger-flexion task. Synchronized electrocorticography (ECoG), finger joint kinematics, electromyography (EMG), and video were recorded.

Inability to flex the index finger during subthreshold stimulation was noted in 3 participants at frequencies >250 Hz when the electrodes were in locations that induced extension of the forefinger at higher amplitudes. Other than these trials, all stimulation events either induced muscle contractions or had no measurable effect.

Data presented here represent the first evidence of (1) movement inhibition of the human hand caused by electrical stimulation of M1, as well as (2) the frequency-dependence of net downstream effects of hand M1 stimulation during task. Our findings support the hypothesis that the mechanism of movement inhibition may be activation of indirect, net-inhibitory mechanisms, as opposed to direct inhibition of the stimulated motor neurons.

There is growing interest in using continuous electrical stimulation of the brain to remap anatomical-functional relationships away from invasive lesions. Achieving this type of neuroplasticity requires a better understanding of the direct and indirect effects of cortical stimulation. Here we demonstrate the frequency-dependent effects of cortical M1 stimulation on volitional finger movement.