Motor cortex stimulation therapy for the treatment of post-stroke pain: operation method and pain alleviation mechanism

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The corticospinal motor evoked potential (MEP) evoked by motor cortex stimulation can be recorded from the epidural space of the spinal cord. The corticospinal MEP response consists of an initial D-wave and a later sequence of volleys termed I-waves. The D-wave, which reflects impulses arising from direct activation of the axons of corticospinal tract neurons and is resistant to anesthetics, was investigated as an intra-operative index for the placement of a stimulating electrode in the epidural space over the motor cortex for the treatment of post-stroke pain.A grid electrode comprising 20 plate electrodes of 5mm in diameter and each separated by 5mm, was placed in the epidural space aiming to cover the motor cortex, sensory cortex, and premotor cortex employing an MRI-guided neuronavigation system in post-stroke pain patients. Initially, the D-wave was recorded with anodal monopolar stimulation of each plate electrode under general anesthesia. Secondly, keeping the grid electrode at the same position, the effect of pain reduction induced by anodal monopolar stimulation of the same epidural plate electrodes was examined using a visual analogue scale (VAS) on a separate day in the awake state without anesthesia.A comparison between the reduction rate of the VAS and the recorded amplitude of the D-wave employing the same stimulation point of the grid electrode revealed a significant correlation. The results obtained indicated the importance of D-wave recording as an intra-operative index for placement of the stimulating electrode over the motor cortex, and we can expect an improvement of the clinical results achieved with motor cortex stimulation.