Esketamine is an antagonist of N-methyl-d-aspartate (NMDA) receptor different from other gamma-aminobutyric acid (GABA) receptor agonists. Recent studies showed that subanesthetic doses of ketamine not only deepen anesthesia but also accelerate recovery from isoflurane anesthesia in mice. It is necessary to verify if it applies to human. Besides inducing behavioral unresponsiveness, an optimal and important goal of general anesthesia is to prevent connected consciousness. The results of many studies support the conclusion that anesthesia-related unconsciousness is a consistent functional disconnection of lateral frontoparietal networks.The goal of this clinical trial is to learn if subanaesthetic doses of esketamine works to accelerate the recovery of consciousness from propofol anesthesia. It will also learn about the change of brain network when administrated the esketamine during propofol anesthesia. The main questions it aims to answer are:

1. Does subanaesthetic doses of esketamine can accelerate recovery from propofol anaesthesia?
2. What will happen to brain network connection after different doses of esketamine during propofol anesthesia?

Inclusion Criteria:

• Aged from 18 years to 50 years
• Patients scheduled for elective operative hysteroscopy
• Willing to sign informed consent

Exclusion Criteria:

• Contraindications of propofol and esketamine
• Contraindications for EEG;
• ASA≥III;
• BMI≥30 kg/m2 or BMI<18 kg/m2;
• The MMSE scale score is lower than the normal value;
• Alcohol or drug abuse;
• Untreated or under-treated hypertension, hyperthyroidism, risk of increased intracranial pressure, audio-visual impairment, history of psychiatric disorders or neurological diseases, malignant tumors or other major diseases;
• Use of other neurological drugs or drugs known to interact with propofol and esketamine in the past 2 weeks;
• Pregnant and lactating women;
• The operation duration is shorter than 15 minutes or longer than 60 minutes.