Transcranial Versus Suboccipital Direct Current Stimulation

Randomized controlled trial, in parallel with cross-control design. Two groups of healthy subjects will be randomly selected to transcranial stimulation group or suboccipital stimulation group. Each group receive in a randomized order a real direct current session and a sham session. The study is based on the hypothesis that the application of direct current sitmulation applied at the suboccipital level produce higher modifications on endogenous pain modulation system than transcranial stimulation.

The development of the project will be based on the Declarations of the World Medical Association of Helsinki. Every subject will be informed about the nature of the study, willingness to participate, the proposed objectives, as well as possible adverse effects that may occur in its implementation. Every subject will be asked to give their signed consent to participate in the study. The study will be suspended at any time, if the patient wishes.

Healthy volunteers will be recruited from the city of Toledo, between the ages of 18 and 40. The detection and selection of the sample will be carried out between the students of the University of Castilla-La Mancha and personnel of the Hospital Nacional de Parapléjicos who meet the inclusion criteria and give their consent voluntarily to participate in the study.

The calculation of the sample size will be carried out using the G \* Power software program (version 3.1), for clinical studies with two intervention groups. Conditioned pain modulation will be chosen as the primary outcome variable. Assuming an α level of 0.05 and a statistical power of 85%, with a moderate effect size for the ANOVA test (0.25).

The experiment will be carried out in the clinical laboratory of the Sensory-Motor Function Research Group of the Hospital Nacional de Parapléjicos. Under attenuated sound conditions, and at a stable temperature in the range of (22 °C-26 °C).

In the first session of the study, a small interview will be carried out to determine if there is any exclusion criterion. The initial measurements will consist of sociodemographic variables and psychological variables, which will then be used to categorize groups and analyze covariates. A parallel randomized controlled trial with cross-control design is proposed. Two groups of healthy subjects will be randomly selected to transcranial direct current stimulation (DCS) group or suboccipital DCS group. Each group receive in a randomized order and with a double blind design a real direct current session and a sham session. An assessment is made before and after each intervention.

Subjects will remain in a sitting position, with their backs resting in a relaxed position. In all interventions a direct current stimulator (DC-stimulator, Neuroconn) will be used.

Eligibility Criteria:
Inclusion Criteria:

* Age between 18 and 40 years.
* Healthy volunteers (without neurological injury and no history of pain in the last 6 months).
* Ability to perform all clinical test and understand the process of the study, as well as obtaining informed consent.
* Tolerance to the application of electrotherapy.

Exclusion Criteria:

* Previous history of surgical intervention at the cervical level.
* Have been treated with an electric current similar to that applied prior to the intervention.
* Sensitivity altered in the area of application of the intervention.
* No commitment to continuity.
* History of neuromuscular disease.
* Epilepsy.
* Injuries, surgery or pain affecting the upper limb.
* Material of osteosynthesis at the cervical level.
* Diabetes.
* History of cancer.
* Cardiovascular disease.
* Presence of pacemakers or any other implanted electrical device.
* Take medication during the study and in the 7 days prior to the study.
* Consumption of narcotic substances during the study and in the 7 days prior to the study.
* Presence of tattoos or any other external agent introduced in the treatment and assessment area (hand).
* Pregnancy.
* Presence of severe and frequent headaches.
* Ulcers or scars in the skin at the location of the electrodes