Inclusion Criteria:  parturient women with a singleton pregnancy; capable of understanding the research requirements and willing to cooperate with the study instructions; aged 18-45; American Society of Anesthesiologists(ASA) physical status I or II; right handed; not taking any drug known to influence the EEG; EPDS scale (Edinburgh Postnatal Depression Scale, EPDS) is used in the last prenatal examination in outpatient clinics , with scores < 10; informed consent is gained from all individual subjects taking part in the study.  Exclusion Criteria:  history of neurological or psychiatric disease; personality disorder; cerebral disease; epidural anesthesia contraindication; multiparous pregnancy.