An interventional study of Transcranial Alternating Current Stimulation and Transcranial Direct Current Stimulation in Health Adult Subjects, sponsored by Hospital de Clinicas de Porto Alegre. Enrolling by invitation at 1 site in Brazil. Open to male participants aged 18 Years to 45 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-09-21.
Sponsored by Hospital de Clinicas de Porto Alegre · Not applicable, Interventional, and Other
Transcranial modulation of the corticospinal sensorimotor pathway is a promising approach in neuroscientic functions. Among the techniques used, transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS) and the application of random noise current stand out. Objective: To compare the e stimulus, in the EEG frequency bands, on Motor Evoked Potentials (MEP) and on the functional activation of the motor cortex, assessed by Functional Near Infrared Spectroscopy (fNIRS) and pain measurements in healthy subjects subjected to a standardized algogenic stimulus. Subjects and Method: This is a randomized, double-blind, controlled and crossover clinical trial, involving the inclusion of 14 healthy male subjects, with complete secondary education, aged between 18 and 40. years. Participants will be randomized to receive Transcranial Direct Current Stimulation (tDCS), (2) Transcranial Alternating Current Stimulation (tACs), (3) Random Noise Current, (4) Simulated Stimulation Session and (5) Rest Session. Experimental conditions will take place in a standard, quiet and bright room. Assessments will include Motor Evoked Potential, Heat Pain Threshold, Motor Area Activation through metabolic activation measured by fNIRS and analysis of EEG frequency waves. After the baseline assessment, participants will undergo a session of transcranial stimulation, followed by an algogenic stimulus with water at zero degrees, immersion of the dominant hand for 1 minute, with rest intervals of 3 minutes between each of the four serial stimuli. After this stimulus session, outcome measurements will be carried out. Expected results: This clinical trial is expected to provide insights into how tDCS, tACs and random stimulation in to an algogenic stimulus. The results may contribute to the development of therapeutic or neuromodulation strategies in clinical conditions where the regulation of the cortico-spinal sensorimotor pathway is relevant.
Hospital de Clinicas de Porto Alegre is the lead sponsor of 456 studies on the registry; 61 are open to participants now.
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Exclusion Criteria:
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Contraindication
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
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Participants receive active transcranial direct current stimulation over the primary motor cortex (M1) during the intervention sessions.
Device: Transcranial Direct Current Stimulation
Participants receive active transcranial alternating current stimulation over the primary motor cortex (M1) during the intervention sessions.
Device: Transcranial Alternating Current Stimulation
Participants receive active transcranial random noise stimulation over the primary motor cortex (M1) during the intervention sessions.
Device: Transcranial Random Noise Stimulation (tRNS)
Participants undergo sham stimulation, experiencing the same setup as active stimulation without actual current delivery.
Device: Sham Stimulation
Participants remain seated with their eyes open for 20 minutes during the rest session, without performing any other task.
Single session of active gamma transcranial alternating current stimulation delivered for 30 minutes using a battery-powered external stimulator. Stimulation is applied through two sponge electrodes (5 × 7 cm) mounted on a neoprene cap. The stimulation frequency is 40 Hz, based on previous gamma-band transcranial alternating current stimulation (tACS) studies. The anode is positioned at C3 (left primary motor cortex, M1), and the cathode over the ipsilateral clavicular region.
Also known as: tACS
Stimulation is delivered using two sponge electrodes (5 × 7 cm) mounted on a neoprene cap. The electrodes are positioned on the scalp according to the international 10-20 system. The anode is placed at position C3 (left primary motor cortex, M1) and the cathode over the ipsilateral clavicular region. The sinusoidal current intensity per channel ranges from ±2 mA. The session duration is 20 minutes.
Also known as: tDCS
Stimulation is delivered using two sponge electrodes mounted on a neoprene cap. The anode is positioned at C3 (left primary motor cortex, M1), and the cathode over the ipsilateral clavicular region. A random current level is generated for each sample at a sampling rate of 1280 samples per second. The random values are normally distributed, following a bell-shaped probability density function. The noise signal contains all frequencies up to half the sampling rate (maximum 640 Hz) and has no DC offset.
Also known as: tRNS
During the sham stimulation session, the tDCS device ramps up the current to 2 mA over 30 seconds and then is immediately turned off. This procedure mimics the sensations of active stimulation without delivering therapeutic current for the remainder of the session.
Also known as: sham
Resting-State EEG Power Spectra Across Frequency Bands (Delta, Theta, Alpha, Beta 1, Beta 2, and Gamma)
Electroencephalography (EEG) will be used to quantify neuronal activity through quantitative EEG (qEEG) analysis. Resting-state EEG power spectra will be analyzed across delta, theta, alpha, beta, and gamma frequency bands, reflecting synchronized neuronal oscillations. EEG data will be recorded using a 20-electrode montage according to the international 10-20 system during an 8-minute resting-state paradigm with alternating eyes-open and eyes-closed conditions. Cortical source localization will be performed using standardized Low-Resolution Brain Electromagnetic Tomography (sLORETA).
Time frame: Immediately before and immediately after the intervention.
Corticospinal Excitability
Corticospinal excitability will be assessed using single-pulse transcranial magnetic stimulation (TMS) applied over the left primary motor cortex. Motor evoked potentials (MEPs) will be recorded from the right first dorsal interosseous muscle, and measures will include resting motor threshold (RMT) and MEP amplitude, with MEPs obtained at 130% of the motor threshold.
Time frame: Immediately before and immediately after the intervention.
Motor Cortex Functional Connectivity
Functional connectivity of the motor cortex will be assessed using functional near-infrared spectroscopy (fNIRS) with a continuous-wave NirScout® system. Optodes will be positioned according to the international 10-10 system to cover the bilateral motor cortex. Data will be acquired during resting-state conditions and during the cold pressor task. Functional connectivity will be analyzed within predefined motor cortex regions of interest.
Time frame: Immediately before and immediately after the intervention.
Heat Pain Threshold
Heat pain threshold will be assessed via quantitative sensory testing (QST) on the left forearm using a thermode that increases temperature from 30°C to 52°C at a rate of 1°C per second. The pain threshold is calculated as the average temperature at which pain is first reported across three trials. Higher values indicate greater pain threshold.
Time frame: Immediately before and immediately after the intervention.
Function of the Descending Pain Inhibitory System
The function of the descending pain inhibitory system will be assessed using the Conditioned Pain Modulation Test (CPM-test). Pain intensity is rated using a verbal numerical rating scale (0 = no pain to 10 = worst possible pain) before (T0) and during (T1) cold-water immersion. The CPM effect is calculated as the difference between pain ratings at T0 and T1, with greater reductions indicating more effective pain inhibition.
Time frame: Immediately before and immediately after the intervention.
Cold Pressor Test Pain Tolerance
Pain intensity and tolerance will be assessed using the Cold Pressor Test, in which participants immerse the non-dominant hand in ice-saturated water (\~1°C) for up to 2 minutes. Pain intensity will be continuously rated using an electronic visual analog scale, allowing calculation of peak pain, mean pain, and area under the curve (AUC) over the test duration.
Time frame: Immediately before and immediately after the intervention.
Plan to share: Yes — Data will be available upon request at wcaumo@hcpa.edu.br after 6 months of publication.
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