Subthalamic neuronal responses to cortical stimulation

Background: Deep brain stimulation of the subthalamic nucleus alleviates motor symptoms in Parkinson's disease patients. However, some patients suffer from cognitive and emotional changes. These side effects are most likely caused by current spread to the cognitive and limbic territories in the subthalamic nucleus. The aim of this study was to identify the motor part of the subthalamic nucleus to reduce stimulation-induced behavioral side effects, by using motor cortex stimulation. Methods: We describe the results of subthalamic nucleus neuronal responses to stimulation of the hand area of the motor cortex and evaluate the safety of this novel technique. Results: Responses differed between regions within the subthalamic nucleus. In the anterior and lateral electrode at dorsal levels of the subthalamic nucleus, an early excitation (similar to 5-45 ms) and subsequent inhibition (45-105 ms) were seen. The lateral electrode also showed a late excitation (similar to 125-160 ms). Focal seizures were observed following motor cortex stimulation. Conclusions: To prevent seizures the current density should be lowered, so that motor cortex stimulationevoked responses can be safely used during deep brain stimulation surgery.