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| (i) The majority of studies, which had clinical and methodological heterogeneity, showed that FER in PD patients worsens after STN DBS compared to before surgery, particularly for negative emotions (sadness, fear, anger, and tendency for disgust). |
| (ii) Most studies showed worse FER in the ON STN condition compared to OFF without dopaminergic medication, while on medication there was no significant difference. |
| (iii) Neurophysiological studies showed modulation of STN alpha activity after DBS in response to emotionally arousing pictures. |
| (iv) Neuroimaging studies showed changes in glucose metabolism or regional blood flow after STN DBS in areas associated with FER such as the orbitofrontal cortex, the anterior cingulate cortex, the fusiform gyrus, or amygdala. |
| (v) Impaired FER after STN DBS is unlikely to be explained by a sole dopamine deficiency resulting from dose reduction postoperatively, but L-dopa might subtly interfere with DBS effects and compensate FER worsening to an extent. |
| (vi) An association between FER worsening after DBS and global cognitive measures could not be shown in most studies, while the contribution of visuospatial abilities postoperative is a controversial issue. |
| (vii) FER worsening might be associated with impairment of inhibition control after STN DBS, whereas the potential involvement of anxiety, depression, or apathy is unclear at the moment. |
| (viii) The surgical trajectory, electrode positioning, stimulation, and current diffusion to nearby limbic STN territory might contribute to DBS effects on FER. |
| (ix) FER worsening after STN DBS can be attributed to the functional role of the STN in limbic circuits and the interference of STN stimulation with neural networks involved in FER such as the connections of the STN with the limbic part of the basal ganglia and pre- and frontal areas. |
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