![]() ![]() 12, 21 – 23 However, the studies on mood provided limited information on the anatomical site of stimulation, usually defining location only relative to the contact with optimal motor benefit or choosing the most ventral contact, without confirming anatomical location. Similar investigations on mood have demonstrated that stimulation of the most ventral electrode contacts were more likely to affect mood. 20 These findings support the notion of functional heterogeneity of the STN with regard to motor and cognitive functioning. One recent study compared the effects of anatomically-defined contact locations on motor and cognitive functions and demonstrated that stimulation of the ventral, rather than dorsal, STN region impaired response-inhibition, as measured with the Go/No-Go task, yet both dorsal and ventral stimulation improved motor functioning, as measured by the Unified Parkinson Disease Rating Scale (UPDRS) motor score, Part 3. Unfortunately, few studies have examined the role of contact location on motor and non-motor responses to STN DBS. ![]() 17 – 19 Although the surgical procedure targets the dorsal portion of the STN to provide optimal motor benefit, the span of electrode contact locations is greater than the size of the STN thus, there is the potential for considerable variability in active contact location, which may account for individual variability in mood response. 13, 15 The different sections of the STN are anatomically connected to different regions of cortex, supporting the hypothesis that the specific location of stimulation may be a mediating factor in the motor and non-motor behavioral responses to STN DBS.Ĭurrent models of STN circuitry propose that functionally-segregated sections of the STN subserve motor, emotion, and cognitive processing. 15, 16 These seemingly inconsistent findings may be due, in part, to differences in electrode contact location. 10 Individual case studies have reported more dramatic and variable effects of stimulation, including uncontrolled fits of laughter, 11 (hypo)mania, 12 – 14 and severe transient depressive symptoms. 9 Another study also found reduced ratings of apathy with stimulators on 10 however, examination of within-subject effects revealed that apathy improved in some, stayed the same in others, and worsened in one patient. ![]() 9, 10 One study reported significantly reduced depression and psychiatric symptoms when bilateral stimulators were turned ON, versus OFF. The few systematic investigations on the effects of bilateral STN stimulation have found reductions in depression, psychiatric symptoms, and apathy. 4 Therefore, recent studies have begun to focus on the mood effects of STN stimulation itself. 6 However, post-surgical changes in mood may reflect not only the effects of stimulation itself but also continued disease-progression, changes in medication, pre-surgical psychiatric history, 7, 8 microlesion effects from electrode implantation, and psychosocial adjustment and adaptation to DBS. 2 – 4 The psychological outcomes of STN DBS have included post-surgical reductions in depression and anxiety symptoms, 5 but STN DBS also may precipitate or exacerbate symptoms of (hypo)mania, depression, anxiety, apathy, and psychosis. Although the motor benefits of deep brain stimulation in the subthalamic nucleus (STN DBS) for Parkinson's disease (PD) are well documented, 1 the effects on mood are highly variable and even detrimental in some instances. ![]()
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