In the elderly patients undergoing elective non-cardiac major surgery, the differences of EEG parameters between those with and without postoperative cognitive dysfunction were observed to determine the characteristic changes of EEG parameters related to postoperative cognitive dysfunction

Inclusion Criteria:

1. aged 65 and above
2. non-cardiac surgery under general anesthesia;
3. American Society of Anesthesiology(ASA) classification I- II
4. Patients aged 18-40 years old are set as background

Exclusion Criteria:

1. patients with central nervous system diseases and mental diseases
2. preoperative minimal mental status examination(MMSE) score<24;
3. ASA status III or higher

3) those who have received less than 5 years of education since entering primary school; 4) history of sedatives or antidepressants use; 5) existed or anticipated alcohol or drug abuse(over 40°c and over 100ml per day for the past 3 months); 6) history of surgery within the previous year; 7) those with severe visual or hearing impairment; 8) those participated in other clinical studies within last 3 months;

1150 cases in the elderly group and 100 cases in the adult background group