Mapping the Structural Substrate of the Somatocognitive Action Network: Enhancing Motor Cortex Stimulation Targeting for Pain.

Introduction: Motor cortex stimulation can treat patients with pain, yet only 40% of patients respond to this treatment. The somato-cognitive action network (SCAN) consists of three nodes interspersed within Penfield’s motor effector regions and is suggested to be involved in processing of pain. Targeting the SCAN may facilitate response of motor cortex stimulation. The configuration of the SCAN nodes resembles the one of the ‘plis de passage’ (PDP) of the central sulcus (CS). Thus, we hypothesize that the PDP may provide a structural substrate of the SCAN and a neuromodulatory target.

Methods: We performed microdissections in sixteen cadaveric human hemispheres, mapped localizations of PDP into standard stereotactic space, and seeded fMRI connectivity across 9,000 resting-state fMRI scans. We performed direct electrical stimulation (DES) of the anterior bank of the CS in 6 patients undergoing craniotomy for lesion resection and recorded motor evoked potentials (MEP) responses of 33 eloquent sites. Stimulation sites were registered with neuronavigation, cortical surfaces were extracted through patient’s imaging and reconstructed using Freesurfer and Brainstorm/MATLAB toolbox. We performed population-based tractography using data from 1065 healthy individuals to map the trajectories and cortical coverage of the three subdivisions of the superior longitudinal fasciculus (SLF) I, II, and III in relation to the precentral gyrus.

Results: We consistently identified a chain of three distinct PDP with increased underlying white matter, in locations analogous to the SCAN nodes. Our fMRI studies demonstrated the connectivity of these sites with the SCAN. Intraoperative recordings during direct electrical central sulcus stimulation further identified inter-effector regions corresponding to PDP locations. Population-based tractography showed minimal overlap between SLF fiber tracts and SCAN nodes.

Conclusion : Our multimodal approach indicates that CS PDP are subserving the SCAN as a structural substrate. More specific neuromodulatory targeting of the PDP might increase the therapeutic effects of M1 stimulation for the treatment of pain.