Why must patients be awake for part of DBS surgery?

Using the standard, microelectrode guided technique for DBS surgery, brain mapping is performed using microelectrodes. The brain mapping procedure is very difficult to perform if the patient is under a general anesthetic or strong sedative. In addition, the procedure is safer if the patient's neurological function (speech and voluntary movement) can be checked periodically during the procedure, which is only possible in an awake patient.