Direct stimulation of the cerebral cortex induces an increase in cerebral blood flow. Although this information is known, it has never been documented during Transcranial Cerebral Electrical Stimulation (TCES), which is a non invasive technique. It is used to modulate the opiate endogenous system, mainly in opioid users but no cerebral blood flow mapping of the anatomic regions involved in this modulation of the opiate system under electrical stimulation has been performed in functional Computerized Tomography.