2.2 Surgical technique The pre-operative fMRI was fused with the neuronavigation MRI. For this purpose, cortex surface rendering technique was performed using the Stealthviz software (Medtronic Inc., Minneapolis, MN, USA) to visualize the cortical areas and determine the central sulcus and the motor cortex, which then was marked on the skin by using neuronavigation. All patients were operated under general anesthesia without muscle relaxation. A small craniotomy (approximately 4 × 4 cm) was carried out over the central sulcus. An electrode was placed perpendicular to the central sulcus in the epidural space (Specify, model 3998, Medtronic Inc., Minneapolis, MN, USA). A phase-reversal somatosensory-evoked potential was used to confirm the position of the central sulcus, thereafter cortical stimulation was performed to map functional motor areas. Following identification of the optimal target, the electrode was sutured to the dura mater. After placement of the electrode, the electrode was tunneled subcutaneously and connected with an internalized pulse generator (IPG) (Medtronic Versitrel and later Prime Advanced) that was implanted in the subclavian space or in a subcutaneous abdominal pocket.