Pain exerts a tremendous cost in healthy care, rehabilitation and lost productivity. It is is associated with a wide range of diseases and their social consequences is a public health problem.

With the progress of neuroscience and studies on the plasticity of the central nervous system, it has been provided a better understanding of the neurobiological mechanisms of pain.

The neurohormone Melatonin stands by having systemic and diverse mechanisms of action, both in physiological and pathological situations, with modulating effects on the process of nociceptive signaling and neurochemical mechanisms such as serotonergic, opioidergic and GABAergic, exerting anti-inflammatory action, analgesic activity among others.

The advent of neuromodulation techniques such as transcranial direct current stimulation (tDCS), which promote changes in neuronal activity and signaling to be effective in conditions of chronic pain by attenuating changes in cortical excitability.

There is clinical evidence of the analgesic effect of Melatonin and tDCS alone. Thus, considering the potential for each isolated intervention and the lack of knowledge of their combined effect, the authors propose the present study to investigate the effect of this combination on the heat-pain detection threshold and the neuroplasticity in the healthy subjects.

The methods are according to the CONSORT guidelines.

Heat pain threshold and tolerance : Quantitative Sensory Testing (QST) will be used on a computer Peltier-based device thermode.

Conditioned Pain Modulation (CPM)-task: Immerssing the non-dominant hand cold water for 1 minute.

Serum Brain Derived Neurotrophic Factor (BDNF).

Transcranial Magnetic Stimulation (TMS) assessment: motor threshold, motor evoked potential, Short intracortical inhibition and intracortical facilitation.

Statistical analyses: Descriptive statistics, Linear and multiple regression analysis, performed with SPSS version18.0.

Inclusion Criteria:

• Male 18-40 years old
• Healthy
• Without medication
• Sign the informed consent

Exclusion Criteria:

• Patients who did not understand the Portuguese
• Acute or chronic pain conditions
• Medical or psychiatric disorders
• History of alcohol or substance abuse
• Neurological disorder
• Use of medications affect in the central nervous system
• Traumatic brain injury
• Neurosurgery
• Metallic implant in the brain