The correct electrode placement within the motor subthalamic nucleus (STN) during the use of deep brain stimulation (DBS) can help normalize such nonmotor cognitive functions as decision making among patients with Parkinson disease (PD). The investigators of the current controlled study sought to examine whether STN-DBS influences risk-reward trade-off decisions in patients with PD, and to analyze its dependency on electrode placement. Findings were published in Movement Disorders.

A total of 17 patients (6 women and 11 men; mean age, 64.94±7.03 years) with idiopathic PD (mean disease duration, 14.23±7.5 years) were treated with STN-DBS for their advanced disease stage. All patients had undergone stereotactic neurosurgery at the Department of Neurosurgery, Charité-University Medicine, Berlin, Germany. The control group was composed of 17 age-matched, healthy individuals (mean age, 65.64±6.78 years) with no history of neurologic or psychiatric conditions.

All patients performed a sequential decision-making task with escalating risk and reward. The researchers computed the effect of STN-DBS on risk-reward trade-off decisions, localized all patients’ bilateral electrodes, and analyzed the predictive value of volume of tissue activated in STN motor and nonmotor territories on changes in participants’ behavior.

A major limitation of the current study is the fact that despite keeping the medication stable between the 2 measurements, the effect of dopamine replacement therapy could not be controlled; that is, the researchers did not test the patients both receiving and not receiving dopaminergic medication.

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Study findings demonstrated that STN-DBS not only improves motor symptoms among patients with PD but also normalizes overly risk-averse decision behavior in these individuals. Intersubject variation in the location of the electrodes might help to explain this behavioral change. In particular, if STN-DBS activated preferentially STN motor territory, patients’ risk-reward trade-off decisions more closely resembled those of healthy control participants.

The investigators concluded that the results of this study support the notion of convergence of different functional circuits within the STN and suggest a positive effect of well-placed STN-DBS on nonmotor cognitive functioning in patients with PD.

Reference

Irmen F, Horn A, Meder D, et al. Sensorimotor subthalamic stimulation restores risk-reward trade-off in Parkinson’s disease [published online November 28, 2018]. Mov Disord. doi: 10.1002/mds.27576