Post-operative cognitive dysfunction (POCD) is a fairly well-documented clinical phenomenon. Investigators will determine whether amantadine can reduce the occurrence of POCD in elderly patients with major abdominal surgery.

Patients who are 60 years old or older for laparoscopic abdominal surgery will be randomly assigned into two groups: 1) no-treatment group, and 2) amantadine-treated group. Each group will have 150 patients. In addition, investigators will need 90 subjects in the control group. The data of these control subjects will be used to normalize the data of the two studied groups to diagnose POCD. The subjects in control groups will also be elderly but without the exposure to anesthesia and surgery.

Inclusion Criteria:

1. major elective gynecological, prostate or bladder surgery patients who are ≥ 60 years old.
2. the surgery is laparoscopic surgery and is expected to last for ≥ 2 hours under general anesthesia and the patient will stay in hospital for at least 7 days after surgery.
3. lack of serious hearing and vision impairment and be able to read so that neurobehavioral tests can be performed.

Exclusion Criteria:

1. Patients are not expected to be alive for longer than 3 months.
2. Mini-mental State Examination (MMSE) [18] score ≤ 23.
3. history of dementia, psychiatric illness or any diseases of central nervous system.
4. current use of sedatives or antidepressant.
5. alcoholism and drug dependence.
6. patients previously included in this study (for patients who have second intra-abdominal surgery during the study period).
7. difficult to follow up or patients with poor compliance.
8. uncontrolled hypertension (> 180/100 mmHg)