Effects of subthalamic nucleus stimulation on motor cortex excitability in Parkinson's disease

Objective: To study the effects of subthalamic nucleus (STN) stimulation on motor cortex excitability in Parkinson's disease (PD). Methods: Fifteen patients were evaluated under off-medication, OFF- and ON-STN conditions, using the UPDRS. We Studied the effects of STN stimulation on motor cortex excitability under three conditions (OFF, ON with chronic therapeutic parameters, ON HighV with a voltage set 10% under permanent side effects threshold), using transcranial magnetic stimulation. We measured the central motor conduction time (CMCT), rest and active motor threshold (MT), F-wave persistence and amplitude, silent period (SP), intracortical inhibition and facilitation at 3, 5 and 15 ms interstimulus intervals (ISI). Results: The UPDRS motor score decreased from 44.4 +/- 14.0 under OFF, to 15.2 +/- 8.0 under ON-STN condition. The CMCT and MT did not change across STN conditions. The F-wave parameters were within normal range under STN stimulation. STN stimulation lengthened the SP and induced facilitation at 15 ms ISI compared to the OFF-STN condition. Conclusion: Therapeutic STN stimulation modulates cortical excitability in PD. High voltage STN stimulation could also act on spinal excitability. Significance: At the motor cortical level, STN stimulation may have a direct effect on intracortical inter-neurons, modifying the balance between excitation and inhibition. (C) 2008 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.