1599-5453 Contact Us KO
Neuromodulation

Transcranial Direct Current Stimulation

Transcranial Direct Current Stimulation

tDCS overview: mechanism of cortical excitability modulation, clinical applications in pain, depression, and neurological rehabilitation, safety profile, and current evidence.

2026-03-28

At a Glance

tDCS overview: mechanism of cortical excitability modulation, clinical applications in pain, depression, and neurological rehabilitation, safety profile, and current evidence.

Definition and Overview

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that delivers a weak direct current of 1-2 mA to the cerebral cortex through electrodes attached to the scalp [1]. Because it can alter cortical neuronal excitability without surgical procedures or anesthesia, it is being actively investigated in neuroscience and clinical fields.

Although tDCS has been studied since the early 20th century, modern clinical research began with the work of Nitsche and Paulus in 2000 [1]. Since then, clinical evidence has been accumulating across diverse areas including depression, chronic pain, stroke rehabilitation, and cognitive function enhancement [2].

Principles and Mechanisms

Electrical Principles

A direct current of approximately 1-2 mA flows between two electrodes (anode and cathode) attached to the scalp. The current passes through the scalp, skull, and cerebrospinal fluid to reach the cerebral cortex [3]. The current density actually reaching the brain is substantially attenuated during passage through the skull.

Neuronal Excitability Modulation

  • Anodal stimulation: Shifts the resting membrane potential of cortical neurons beneath the electrode toward depolarization, increasing spontaneous firing rates. Cortical excitability is enhanced [1].
  • Cathodal stimulation: Conversely induces hyperpolarization, reducing neuronal firing rates. Cortical excitability is inhibited [1].

Synaptic Plasticity

The excitability changes induced by tDCS persist not only during stimulation but also for a period afterward (tens of minutes to several hours). This is attributed to plasticity changes resembling long-term potentiation (LTP) and long-term depression (LTD) related to NMDA receptor activity, calcium-dependent mechanisms, and changes in BDNF (brain-derived neurotrophic factor) expression [2].

Clinical Indications

According to international clinical guidelines (2017), evidence levels have been established for the following conditions [2].

Established Indications

  • Fibromyalgia: Anodal stimulation of the primary motor cortex shows significant efficacy in pain reduction.
  • Depression: Anodal stimulation of the left dorsolateral prefrontal cortex (DLPFC) is effective in improving depressive symptoms. Meta-analyses have demonstrated significant reduction in depressive symptoms compared to sham stimulation, with efficacy also reported in treatment-resistant depression [4].
  • Post-stroke motor rehabilitation: Stimulation of the motor cortex in the affected hemisphere promotes motor recovery.
  • Post-stroke aphasia: Stimulation of language centers provides adjunctive benefit for language recovery.

Indications Under Investigation

  • Chronic pain and neuropathic pain
  • Autonomic nervous system regulation
  • Cognitive enhancement and adjunctive therapy for Alzheimer's disease
  • Obsessive-compulsive disorder, PTSD
  • Chronic fatigue syndrome
  • Cognitive and gait function in Parkinson's disease

Effects on the Autonomic Nervous System

tDCS stimulation targeting the left prefrontal cortex (DLPFC) or insular cortex can influence the central autonomic network (CAN), which is involved in autonomic nervous system regulation. Studies have reported changes in heart rate variability (HRV) and blood pressure responses following tDCS, and research into the mechanisms of autonomic function improvement is ongoing [2].

The insular cortex, in particular, is a key cortical structure for autonomic regulation, and the hypothesis that tDCS stimulation of this area may modulate sympathetic-parasympathetic balance is being actively investigated.

Procedure

Equipment and Electrode Placement

Standard tDCS devices deliver a stable direct current of 1-2 mA. The electrodes are rectangular or circular sponge pads approximately 35 cm² in size, thoroughly moistened with saline prior to the procedure to reduce skin-electrode contact impedance [3].

Target Sites

The positions of the anode and cathode are determined according to the therapeutic objective. For example, in depression treatment, the anode is placed over the left DLPFC (F3 position per the 10-20 EEG system), and the cathode is placed over the right supraorbital region [4].

Session Duration and Frequency

Each session lasts 20-30 minutes, and a treatment course typically consists of 5-20 sessions (daily or every other day) depending on the condition and therapeutic goals. It can be performed on an outpatient basis, and other therapies or cognitive training can be conducted concurrently during sessions.

Safety

According to the 2016 international safety guidelines, tDCS administered within the recommended parameters (current density below 0.029 mA/cm², total charge below 7.2 C) is safe with no serious adverse effects [3].

Mild side effects, including skin erythema at the electrode site, tingling, and headache, are rarely reported. Decreased concentration and drowsiness may also occur transiently.

Absolute contraindications: Intracranial metallic implants (DBS electrodes, aneurysm clips), intracranial electrical stimulation devices

Relative precautions: Epilepsy, pregnancy, scalp skin lesions, cardiac pacemakers

Comparison of tDCS and TMS

| Parameter | tDCS | TMS |
|------|------|-----|
| Stimulation method | Weak direct current | Strong magnetic field-induced current |
| Mechanism of effect | Excitability modulation | Direct neuronal firing |
| Device size | Small, portable | Large, stationary |
| Session duration | 20-30 minutes | 30-40 minutes |
| Noise/discomfort | Minimal | Clicking sound, scalp sensation |
| Insurance coverage | Limited | Partially covered |
| Evidence base | Growing | More evidence accumulated |

Frequently Asked Questions

A weak direct current of 1-2 mA passes through the cerebral cortex via anode and cathode electrodes attached to the scalp. The brain area receiving anodal stimulation becomes more excitable, while the cathodal area is inhibited. These changes persist for a period after stimulation through synaptic plasticity mechanisms.

TMS directly fires neurons using strong magnetic fields, producing rapid and clear effects, but requires large equipment and higher costs. tDCS modulates only neuronal excitability with microcurrents (without inducing firing), so the equipment is small and easy to use, and home-use devices are also being developed. The two methods overlap in some indications but have different strengths.

There is evidence supporting its use in depression (particularly treatment-resistant), chronic pain (fibromyalgia, neuropathic pain), post-stroke rehabilitation, cognitive function improvement, and autonomic imbalance regulation. Studies have reported symptom improvement in more than 50% of depression patients [4].

During tDCS, mild tingling, warmth, or itching may be felt at the electrode sites, but most patients tolerate the procedure well. No anesthesia is required, and patients can read or converse during the session. Saline-soaked sponge electrodes are used to minimize skin irritation.

When administered at appropriate intensity (2 mA or less) and duration (within 20-30 minutes), tDCS is a safe procedure with no reported serious adverse effects within international safety guidelines. Skin irritation, headache, and fatigue may occur rarely. Patients with epilepsy or intracranial metallic implants must consult a specialist before undergoing the procedure.

For depression or chronic pain, an intensive treatment course of 10-20 sessions administered daily or every other day is typically recommended. A single session may produce temporary effects, but repeated sessions are necessary for sustained results. The schedule is determined in consultation with a specialist based on treatment response and goals.

References

  1. [1] Nitsche MA, Paulus W (2000). "Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation." Journal of Physiology, 527: 633-639. DOI PubMed
  2. [2] Lefaucheur JP, Antal A, Ayache SS, Benninger DH, Brunelin J, Cogiamanian F, Cotelli M, De Ridder D, Ferrucci R, Langguth B, Marangolo P, Mylius V, Nitsche MA, Padberg F, Palm U, Poulet E, Priori A, Rossi S, Schecklmann M, Vanneste S, Ziemann U, Garcia-Larrea L, Paulus W (2017). "Evidence-based guidelines on the therapeutic use of transcranial direct current stimulation (tDCS)." Clinical Neurophysiology, 128: 56-92. DOI PubMed
  3. [3] Bikson M, Grossman P, Thomas C, Zannou AL, Jiang J, Adnan T, Mourdoukoutas AP, Kronberg G, Truong D, Boggio P, Brunoni AR, Charvet L, Fregni F, Fritsch B, Gillick B, Hamilton RH, Hampstead BM, Jankord R, Kirton A, Knotkova H, Liebetanz D, Liu A, Loo C, Nitsche MA, Reis J, Richardson JD, Rotenberg A, Turkeltaub PE, Woods AJ (2016). "Safety of transcranial direct current stimulation: evidence based update 2016." Brain Stimulation, 9: 641-661. DOI PubMed
  4. [4] Brunoni AR, Moffa AH, Fregni F, Palm U, Padberg F, Blumberger DM, Daskalakis ZJ, Bennabi D, Haffen E, Alonzo A, Loo CK (2016). "Transcranial direct current stimulation for acute major depressive episodes: meta-analysis of individual patient data." British Journal of Psychiatry, 208: 522-531. DOI PubMed
  5. [5] Antal A, Alekseichuk I, Bikson M, Brockmöller J, Brunoni AR, Chen R, Cohen LG, Dowthwaite G, Ellrich J, Flöel A, Fregni F, George MS, Hamilton R, Hauser J, Herrmann CS, Hummel FC, Lefaucheur JP, Liebetanz D, Loo CK, McCaig CD, Miniussi C, Miranda PC, Moliadze V, Nitsche MA, Nowak R, Padberg F, Pascual-Leone A, Popescu M, Priori A, Rossi S, Rossini PM, Rothwell J, Rueger MA, Ruffini G, Schellhorn K, Siebner HR, Ugawa Y, Wexler A, Ziemann U, Hallett M, Paulus W (2017). "Low intensity transcranial electric stimulation: safety, ethical, legal regulatory and application guidelines." Clinical Neurophysiology, 128: 1774-1809. DOI PubMed

Related Articles

Insomnia
tDCSTranscranial Direct Current StimulationNon-invasive Brain StimulationCortical StimulationNeuromodulationAutonomic tDCSDepression TreatmentChronic Pain

This content is provided for informational purposes only and is not a substitute for professional medical advice. If you have symptoms, please consult a qualified physician.

Are you experiencing related symptoms?

Get an accurate diagnosis at OSANG Neurosurgery.

02-514-8887 KakaoTalk Consultation