The aim of this study is to evaluate, versus placebo, the analgesic efficacy of the opercular-insular cortex stimulation with Transcranial Direct Current Stimulation (tDCS), in both healthy subjects and chronic neuropathic pain patients. In healthy subjects analgesia by tDCS will be assessed using both laser stimuli and cold pressor test. In patients the assessment regards their chronic pain (ratings for ongoing, evoked and paroxysmal pain, sleep and fatigue). Opercular-insular stimulation is obtained via a combined 6-electrode montage and by bi-vestibular stimulation (since vestibular pathways reach the posterior insular cortex). In patients, three separate conditions (two active and one sham) will be tested in randomised order. In healthy subjects, two other conditions are added to control for attention and distraction confounders.

Inclusion Criteria:

• healthy subjects aged from 18 to 70 years, male or female, with social security protection, fully informed and having given their written consent.
• patients aged from 18 to 80 years, male or female, with social security protection , fully informed and having given their written consent.
• pharmacoresistant neuropathic pain during at least one year,
• without any change of the pharmacological treatment since at least one month

Exclusion Criteria:

In healthy subjects only:

• history of chronic pain
• analgesic medication within 24h before stimulation

For patients only: new analgesic treatment within 1 month before consent

for both:

• drug addiction, headache, epilepsy
• ferromagnetic intracranial device
• implanted stimulator
• recent neurosurgery and open wound of the scalp.
• absence of contraceptive method for women of childbearing age