Neurophysiologic aspects of deep brain stimulation

Implanting electrodes for deep brain stimulation (DBS) allows performance o f a number of different neurophysiologic studies. Before definitive interna lization of the device, recording and stimulation through the electrodes is possible. Stimulation of the globus pallidum produced a mixture of excitat ion and inhibition of ongoing muscle activity. The excitatory response is p robably produced by activation of the large-diameter fibers of the corticos pinal tract. Stimulation of the thalamus is mainly associated with EMG inhi bition. These findings indicate that the effect of stimulation may vary in different targets and that the mechanism of action of DBS is heterogeneous. A different type of study concerns those undertaken after chronic DBS of t he subthalamic nucleus (STN) and globus pallidum internum (GPi) in parkinso nian patients. Cortical mechanisms subserving movement preparation and exec ution have been assessed. The main findings were that stimulation had a mor e prominent effect on execution than on preparation and that this was great er in patients treated with STN DBS than GPi DBS.