**7. Connectomic DBS in PD**

Indeed, the use of human connectome has been studied extensively in the field of DBS surgery, especially for major movement disorder indications such as PD. In general, electrode localization is important in the success of surgery. Historically, lesion-based localization at surgical targets, namely STN or GPi, is found to improve motor symptoms in PD patients. However, as increasing evidence points out that DBS works by restoring the connectivity of abnormal networks to a physiological state, [57, 58] more studies have investigated the relationship between connectivity-based localization and treatment outcome of DBS surgery. Horn et al. reported that with the use of normative connectome, structural connectivity to supplementary motor area (SMA), superior frontal gyrus and cerebellum were associated with good clinical response. Also, structural and functional connectivity were independent predictors of clinical improvement of STN DBS [45].

Next, it has been postulated that if different surgical targets would modulate the same circuit in PD patients and affect treatment response. Sobesky et al. showed that based on normative connectome atlas, connectivity profiles seeding from either STN or GPi DBS electrodes were highly similar, suggesting that irrespective of the surgical target, the network modulated by DBS largely overlaps [64]. Moreover, in both groups, functional connectivity to the frontal lobe, especially SMA and adjacent cingulate, middle and inferior temporal gyri, inferior parietal gyri and motor cerebellum were associated with good clinical outcome [64]. Nonetheless, despite the marked similarity in the circuitry modulated by both DBS, the treatment response in the two groups varied. For bradykinesia-rigidity symptoms, connectivity profile was associated with significant improvement and shared considerable similarity in both groups. In contrast, the results for tremor were different, suggesting that the networks modulated by effective neurostimulation at different targets, though similar, may have a small discrepancy [64].

Electrophysiological data has long been used as markers for lesion-based neuromodulation surgeries in PD. For example, local field potential (LFP) can serve as a
