Introduction: Active contact location is a key driver for clinical success in STN DBS. This study aims to generate somatotopies of limb effect (upper extremity [UE] vs. lower extremity [LE]) and laterality (contralateral [CL] vs. ipsilateral [IL]), based upon categorization of the UPDRS Part III scoring symptom, and its spatial interpolation.

Methods: PD patients receiving single-sided STN DBS, with 3 month post-operative follow-up were identified. Implantations were performed using a CRW frame-based technique, using local anesthesia, and microelectrode recordings (MER). After initial targeting, MERs and macrostimulation guided intraoperative trajectory adjustments. Patients were assessed pre-operatively and post-operatively (UPDRS Part III). The subcomponents of this scale were aggregated into quantitative UE/LE and CL/IL scores, and a percent reduction. Active contact locations were derived from postoperative MRI. An ordinary "kriging" method generated spatial topographies for each subcategory, at axial slabs (z=-3.5 and -4.5 mm). Fidelity of interpolation was estimated using a cross-validation model.

Results: DBS resulted in a mean CL and IL symptom reduction of 56.7±26.8% and 15.9±51.8%, respectively. Successful interpolation was performed with good validation (R2>0.80). CL UE and LE symptom reduction was best associated with leads placed within the entire STN or the caudal ZI . However, IL UE symptom reduction was found in regions anterior and lateral to the STN. IL LE effect was limited to the regions within the central and posterior STN . Generally, IL UE reduction was found in more lateral regions, than LE effects, though significant overlap exists.

Conclusions: Based on these reconstructions, differing limb and laterality somatotopies within and around the STN. Further studies are required to determine if targeting for ipsilateral effect is a valid surgical planning strategy. A better spatial understanding STN function may be critical in direct and customized targeting strategies.

Patient Care: Somatopies described in this research could contribute to optimization of surgical plans for STN DBS, suggesting targets that differentially affect laterality and limb.

Learning Objectives: 1. To discuss the functional organization of the STN. 2. To discuss possible ipsilateral pathways of DBS efficacy. 3. Contribute to outcome driven DBS targeting.

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