Patients suffering from PD often experience neuropsychiatric symptoms, which might even be the first detectable symptom of this neurodegenerative process [
37]. DBS has great potential to relieve motor symptoms and may also have a beneficial effect on many non-motor symptoms [
3,
27,
38]. One of the main challenges in the management of advanced PD and STN DBS is increased apathy after STN DBS with a high impact on quality of life [
7]. The pathophysiology of apathy in PD, and particularly in the case of STN DBS, is still not fully understood; however, the relation between apathy and medication reduction and a direct stimulation effect are recognized as potential factors [
9]. Because our proposed intervention is only a minor adjustment in the stimulation settings, this adjustment has the potential to improve the quality of life of many PD patients relying on STN DBS without many side effects. The application of STN DBS may subsequently be expanded as a patient’s mood might benefit from the treatment of invalidating PD motor and hypodopaminergic non-motor symptoms, as well as the possible reduction of hyperdopaminergic side effects that are allowed by lowered LEDD following STN DBS. The reduction of apathy might further increase physical health of people with PD who might have been limited in their activities by apathy and improve their social life. The study design has some limitations: first, the contact point that will be selected for the intervention will not be based on MRI imaging. This practice has been chosen because of the concept generalization; in this way, our intervention could be applied regardless of access to visualization of the STN subregions which are difficult to distinguish. The imaging of these subregions would preferably be done requiring imaging instruments on the level of 7-Tesla MRI scans, which is almost exclusively used for research and not clinical practice. Another argument for our decision was the desire to not influence the selection of intervention based on our hypothesis but to apply the intervention that has worked for previous patients [
18]. However, this contact point was not necessarily closest to the motor region of the STN. Benefits of choosing the contact closest to the motor region of the STN on MRI imaging might have been the following: a more optimal motor response with possibly less required adjustments in LEDD or DBS current and less risk of stimulating adjacent regions with possible additional side effects. Second, we chose an apathy score of 14 or more on the SAS as inclusion criteria instead of an increased SAS score between pre- and postoperative assessments, which would more likely indicate solely STN DBS-induced apathy. Our argument for this decision was also generalizability because STN DBS-treated patients with apathy will have rarely available preoperative apathy scores for comparison. Furthermore, other studies found that STN DBS improved apathy or PD-related dysphoria without an earlier increase of apathy following STN DBS [
39,
40]. Third, this study focused on apathy, although apathy is associated with other disorders. For example, apathy and depression share many features and might have some common pathophysiology when related to PD. We chose to include the most common disorders as secondary outcomes and not exclude participants with a current depressive or psychotic episode [
3,
9,
41,
42]. Fourth, enrollment of participants was possible after only 3 months of STN DBS which might arguably be too soon because many centers optimize DBS stimulation and dopaminergic medication in the first 6 months. We chose the timepoint of at least 3 months because of four reasons: optimization of DBS and medication within 3 months are prioritized in our center, an earlier study showed that apathy did not further increase after 3 months [
43]. cognitive decline might develop in the timespan of DBS surgery and optimization, and waiting on drugs for the treatment of depressive episodes to have effect was deemed inconsequential because this study aimed to treat apathy regardless of depressive symptoms. Fifth, 1 month of intervention is relatively short, we opted for this period because in our case study, and the direct stimulation effect was resolved within days to weeks [
18]. This fast effect was also present in another case study [
7]. To our knowledge, these are the only intervention reports on an imaging-supported STN DBS stimulation effect on apathy. However, relative to most non-motor symptoms and psychiatric disorders, an intervention of 1 month is short, and this could restrict the effectiveness of the trial. We hypothesize that switching stimulation to the motor region of the STN could be an optimization for DBS in PD, with an effect on multiple psychiatric symptoms and quality of life.