 Deep brain simulation DBS is an increasingly popular treatment for movement and psychiatric disorders such as Parkinsons disease and dystonia. These patients are quite sensitive to anesthetics and use of depth of anesthesia monitors are often needed to titrate the anesthetics. The calibration of BIS and entropy monitors has been done only on subjects with no neurological diseases. The investigators plan to record BIS and entropy readings during general anesthesia GA for the internalization of DBS electrodes. This would be useful as there are very few studies in this subset of patients with regards to DOA monitoring. Ashraf argued that the EEG may be altered under these circumstances and hence produce invalid BIS readings. Pemberton et al. studied patients undergoing tumour surgery using a sleep- awake-sleep anaesthesia technique. They found a poor correlation between BIS values and the observers assessment of anesthesia level, suggesting that BIS is not a reliable tool for patients with brain abnormalities. The purpose of this study was to investigate whether BIS and entropy are helpful in titrating DOA in patients undergoing neurosurgical procedures or suffering from neurological diseases as they were frequently excluded from validation studies of the BIS monitoring device. 