Negative motor areas: functional connectivity using stereoelectroencephalography

Negative motor areas are cortical regions that, when stimulated, determine an inability to pursue voluntary movement or sustain voluntary muscle contraction without producing any other symptoms or signs. This is the first study that addresses the localization and functional connectivity of the negative motor network using the stereoelectroencephalographic method in patients explored for focal drug-resistant epilepsy. Responses to high frequency intracranial stimulations in 225 consecutive patients from two epilepsy centers (115/110) were reviewed. Forty-one stimulations (performed in 23 patients) eliciting the first overt sign of negative motor manifestations were included. Functional connectivity changes were assessed by evaluating the h² correlation coefficient, intersignal dependencies and the direction of coupling. We assessed the mean node strength to highlight the drivers of the negative motor networks. Negative motor responses were evoked by stimulating the following structures: middle cingulate cortex, supplementary motor area, lateral premotor cortex, dorsomedial and dorsolateral prefrontal cortex, precentral gyrus, frontal, Rolandic and parietal operculum, insular cortex, postcentral gyrus and superior parietal lobule. The negative motor network showed an asymmetric representation, with a broader localization in the left hemisphere and a more focal distribution in the right hemisphere, notably in the cingulate cortex. The main hubs involved pertain to the premotor-prefrontal region. In addition to regions already described, the insular cortex and the frontal operculum seem to be involved in the negative motor network. Finally, there seems to be an asymmetry regarding current intensities, with a lower threshold in the left hemisphere.