*4.2. Individual Tractography*

Another way in which DBS e fficiency can be improved is to ameliorate the implantation of electrodes with the usage of individualized, patient-specific, deterministic tractography targeting. Riva-Posse et al. (2018) used individualized patient-specific tractography targeting for SCC-DBS surgeries in TRD patients, aiming at the convergence of the four white matter bundles: the forceps minor, uncinate fasciculus, cingulum, and fronto-striatal fibers. This resulted in a response rate of 81.8% and a remission rate of 54% after a one year trial period, which proved greater than the previous open-label trials [83]. In a recent study, di ffusion tensor imaging (DTI) tractography was used to target SCC-DBS more optimally, and the authors examined the impact of tract activation on clinical response at 6 and 12 months. Stimulation of vmPFC pathways by SCC-DBS was associated with a positive response and stimulation of the cingulum was associated with a 6 month, but not a 12 months DBS response. Monopolar stimulation of 130 Hz was applied with either pulse width (90–450 μs) or amplitude (4–8 V) progressively increased every month, based on response status. Patients were changed to bipolar settings if monopolar stimulation caused adverse e ffects. It was speculated that targeting more ventral, rather than the dorsal mPFC projections, might improve the response [84].

### *4.3. Combining Deep Brain Stimulation with Cognitive-Behavioral Therapy*

It is plausible that better therapeutic outcomes could be achieved if DBS is applied in combination with concurrent treatments, such as pharmacotherapy with antidepressants or cognitive-behavioral therapy (CBT) in TRD. Studies focusing on the added e ffect of concurrent treatments to DBS have not been conducted in patients with TRD. The results from studies in OCD patients treated with DBS show that adding CBT to DBS has added beneficial e ffects [85]. Studies targeted at revealing the added effects of concomitant treatments after DBS for TRD would also provide information that may facilitate establishing a treatment algorithm to determine the place of these treatments in DBS patients.
