The purpose of the study is to compare the analgesic effect of 2 mA anodal direct current stimulation on the right primary motor cortex (M1) (tDCS) with a similar stimulation on the spine (D10) (tsDCS) in healthy volunteers (HV) followed by a pilot study in patients suffering of endometriosis-related chronic pelvic pain (CPP)

- 2 groups of 5 HV will receive tDCS or tsDCS (2mA, anodal, 20min) and the thermonociceptive threshold will be measured before and after the stimulation over the abdomen (hypogastric). The HAD scale and SF-36 will also be tested.

The treatment(s) that produces the greatest increase in pain thresholds will be chosen to treat 10 patients.

- 10 patients suffering from endometriosis-related chronic pelvic pain will be treated by the most efficient treatment (tDCS or tsDCS) for 4 weeks (5 daily 20-min sessions per week), or, if no treatment modality was superior in HV, 5 patients will be treated by tDCS and 5 by tsDCS. Patients will fill in daily a dedicated diary 2 weeks before treatment, during the4-week treatment period and after this period as long as their pain level remains below 80% of their baseline pain intensity (VAS). Analgesic intake will also be monitored as well as HAD and SF-36 scores.

Inclusion Criteria:

• HV: good health.
• CPP patients: surgical diagnosis of endometriosis within the last 10 years; diagnosis of chronic pelvic pain (according to ACOG); mean VAS pain score >4 during severe episodes.

Exclusion Criteria:

• HV: chronic pain disorder; no regular medication or illicit drug use.
• CPP patients: pregnancy; other medical or psychiatric condition interfering with pelvic pain assessment.

anonymized data will be made available on request via e-mail