Is brain‐responsive neurostimulation in eloquent cortex without symptoms?

Abstract

We read with interest the article by Jobst et al.1 on responsive neurostimulation in eloquent areas. The authors report that none of the patients showed stimulation-related adverse effects, such as involuntary motor activity or decreased motor performance when stimulation involved the primary motor cortex. This conclusion was not supported by observations during stimulation itself or by functional assessments, but by the fact that no adverse effects were reported. Patients with motor seizures may not notice the stimulation effect on performance, because they usually already experience decreased performance due to the seizures themselves. This may explain why no adverse events were reported, whereas stimulation may still have affected motor function. It has been shown that therapeutic studies often underestimate side effects when seizure outcome is the main focus, and that judging adverse events requires detailed questioning.2 In the discussion, Jobst et al. mention that it is not known whether stimulation should be applied at or near the seizure focus, for example, in relevant propagation pathways or networks. Stimulation at the seizure focus may seem most straightforward, but anyone performing cortical stimulation will recognize the difficulty of stimulating the motor cortex without adverse effects. Pericentral cortex has the lowest stimulation threshold, and a small (0.1 mA) increase in intensity may induce visible contractions and seizures, especially in the limb representation part of the sensorimotor cortex.3, 4 In brief, we still need to be convinced that cortical stimulation can be without symptoms in eloquent motor cortex. Besides this critical note, we would like to thank the researchers involved in the NeuroPace trial for their inspiring and important work. This work was supported by the Dutch Epilepsy Foundation grant no. 17-07 (to F.L.). The authors have no conflicts of interest to disclose. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this report is consistent with those guidelines.