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Somatotopic organization of the ventral nuclear group of the dorsal thalamus: deep brain stimulation for neuropathic pain reveals new insights into the facial homunculus

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Abstract

Deep Brain Stimulation (DBS) is an experimental treatment for medication-refractory neuropathic pain. The ventral posteromedial (VPM) and ventral posterolateral (VPL) nuclei of the thalamus are popular targets for the treatment of facial and limb pain, respectively. While intraoperative testing is used to adjust targeting of patient-specific pain locations, a better understanding of thalamic somatotopy may improve targeting of specific body regions including the individual trigeminal territories, face, arm, and leg. To elucidate the somatotopic organization of the ventral nuclear group of the dorsal thalamus using in vivo macrostimulation data from patients undergoing DBS for refractory neuropathic pain. In vivo macrostimulation data was retrospectively collected for 14 patients who underwent DBS implantation for neuropathic pain syndromes at our institution. 56 contacts from 14 electrodes reconstructed with LeadDBS were assigned to macrostimulation-related body regions: tongue, face, arm, or leg. 33 contacts from 9 electrodes were similarly assigned to one of three trigeminal territories: V1, V2, or V3. MNI coordinates in the x, y, and z axes were compared by using MANOVA. Across the horizontal plane of the ventral nuclear group of the dorsal thalamus, the tongue was represented significantly medially, followed by the face, arm, and leg most laterally (p < 0.001). The trigeminal territories displayed significant mediolateral distribution, proceeding from V1 and V2 most medial to V3 most lateral (p < 0.001). Along the y-axis, V2 was also significantly anterior to V3 (p = 0.014). While our results showed that the ventral nuclear group of the dorsal thalamus displayed mediolateral somatotopy of the tongue, face, arm, and leg mirroring the cortical homunculus, the mediolateral distribution of trigeminal territories did not mirror the established cortical homunculus. This finding suggests that the facial homunculus may be inverted in the ventral nuclear group of the dorsal thalamus.

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All authors contributed to the study conception and design. Material preparation and data collection were performed by ZR, LGR, MT, and WW. Data analysis and figure preparations were performed by ZR, LGR, and XRS. The first draft of the manuscript was co-written by ZR and LGR and all authors commented on previous versions of the manuscript. AAB provided supervision, resources, and methodology. All authors read and approved the final manuscript.

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Correspondence to Ziad Rifi.

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This is a retrospective study. The Institutional Review Board has confirmed that no ethical approval is required (IRB##23-000204).

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The Institutional Review Board has provided waiver of patient consent for participation or publication (IRB##23-000204).

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Rifi, Z., Remore, L.G., Tolossa, M. et al. Somatotopic organization of the ventral nuclear group of the dorsal thalamus: deep brain stimulation for neuropathic pain reveals new insights into the facial homunculus. Brain Struct Funct 229, 349–358 (2024). https://doi.org/10.1007/s00429-023-02733-9

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  • DOI: https://doi.org/10.1007/s00429-023-02733-9

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