1. Design and participants: The patients with MDD were screened from the hospital, age- and gender-matched healthy controls were recruited by advertising from the community who signed written informed consent before participation.
2. Assessments: The 17-item Hamilton Depression Rating Scale (HRSD-17) , Montgomery-Asberg Depression Rating Scale (MADRS), the Clinical Global Impression-Severity scale (CGI-S), and 14-item Hamilton anxiety scale (HAMA) were assessed at baseline and after 8 weeks' treatment with escitalopram for patients with MDD. As for healthy volunteer, these measures were evaluated only once. In addition, all participants were assessed Pittsburgh Sleep Quality Index (PSQI) and Insomnia Severity Index (ISI).
3. Treatment: Each patient was provided with escitalopram.
4. Collection of peripheral blood samples: Test the levels of plasma melatonin at 4 h intervals for 24 h from all participants.
5. Sleep and EEG recordings: The PSG of participants was evaluated for one night at baseline (all participants) and 8 weeks treatment (MDD).
6. Analysis the PSG architecture and power ratio.
