Physiological effects of subthalamic nucleus deep brain stimulation surgery in cervical dystonia

Background Subthalamic nucleus deep brain stimulation (STN DBS) surgery is clinically effective for treatment of cervical dystonia; however, the underlying physiology has not been examined. We used transcranial magnetic stimulation (TMS) to examine the effects of STN DBS on sensorimotor integration, sensorimotor plasticity and motor cortex excitability, which are identified as the key pathophysiological features underlying dystonia. Methods TMS paradigms of short latency afferent inhibition (SAI) and long latency afferent inhibition (LAI) were used to examine the sensorimotor integration. Sensorimotor plasticity was measured with paired associative stimulation paradigm, and motor cortex excitability was examined with short interval intracortical inhibition and intracortical facilitation. DBS was turned off and on to record these measures. Results STN DBS modulated SAI and LAI, which correlated well with the acute clinical improvement. While there were no changes seen in the motor cortex excitability, DBS was found to normalise the sensorimotor plasticity; however, there was no clinical correlation. Conclusion Modulation of sensorimotor integration is a key contributor to clinical improvement with acute stimulation of STN. Since the motor cortex excitability did not change and the change in sensorimotor plasticity did not correlate with clinical improvement, STN DBS demonstrates restricted effects on the underlying physiology.