The main purpose of the study is to assess whether repeated sessions of repetitive trancranial magnetic stimulation (rTMS) applied on left dorsolateral prefrontal cortex main boost the pain thresholds.

Pain is the largest health-related burden on society and, despite many decades of pain research, there are still few effective treatments. Since pain experience is a construct of the central nervous system (CNS), chronic pain has been recently thought to be a CNS disorder.

Repetitive transcranial magnetic stimulation (rTMS) is a safe, non-invasive technique for cerebral cortex stimulation and the clinical applications of which have expanded considerably in recent years. Recent studies have been shown that 'classical' rTMS to different cortical areas temporary reduce chronic and acute pain, suggesting that rTMS may ´have some clinical application in future management of chronic pain. However, new rTMS paradigms involving theta burst stimulation (TBS) have recently been described with the major clinical advantage to be much shorter than 'classical' rTMS. The investigators hypothesize that cTBS would yield analgesic effects similar to or, possibly, even stronger than those produced by 'classical' rTMS. The investigators will carry out a sham-controlled, randomized, double-blind, crossover study in healthy volunteers, to compare the analgesic effects of two rTMS protocols over dorsolateral prefrontal cortex: classical high-frequency rTMS (10 Hz), and TBS. As rTMS-induced analgesia may be dependent on changes in pain modulatory systems, the investigators will analyze the effects of the stimulation on conditioned pain modulation (CPM). More specifically, the investigators will compare the effects of multiple sessions of rTMS on the inhibition of a test experimental stimulus induced by heterotopic noxious stimuli, to assess possible changes in diffuse noxious inhibitory controls.

Inclusion Criteria:

• Healthy volunteers

Exclusion Criteria:

• Major medical conditions