Transcranial Direct-Current Stimulation (tDCS)

Last edited on May 9, 2024

Transcranial Direct-Current Stimulation (tDCS) is a form of brain stimulation that delivers a continuous low-amplitude electrical current to a specified cortical region using scalp electrodes. Stimulation over the cortex increases cortical excitability through depolarization of neuronal membrane potential. By contrast, cathodal stimulation decreases cortical excitability through hyperpolarization of the membrane potential.

tDCS is based on two principles:
- Anodal stimulation increases cortical excitability by depolarizing of neuronal membrane potential.
- Cathodal stimulation decreases cortical excitability by hyperpolarizing of the membrane potential.
Repeated use of tDCS is thought to lead to neuroplasticity effects similar to long-term potentiation (LTP) and/or long-term depression, possibly mediated via N-methyl-d-aspartate receptor (NMDA)-dependent mechanisms.^[1]

The optimal stimulus parameters, frequency, or duration of tDCS remain under investigation.
In studies in patients with major depressive disorder have used anodal stimulation over the left dorsolateral prefrontal cortex (DLPFC) with the cathode used as a ground over a noncortical region or combining left DLPFC anodal stimulation with right DLPFC cathodal stimulation.
- A minimum stimulation with 2 milliamperes (mA) for at least 30 minutes per day for 2 weeks for an antidepressant effect

There are current mixed results for the use of tDCS in depression.^[2] As a result, tDCS is thus recommended as a third-line treatment for MDD.
A recent rigorous, double-blind control trial showed that there is no benefit from tDCS compared to sham (placebo) treatment in major depressive disorder.^[3]
- Similar negative studies have shown no improvement with home-based tDCS.^[4]

Advantages of tDCS include ease of use, low cost, portability, and potential for home-based use. It can also be easily used in combination with other treatments, and has low potential for adverse effects.
tDCS may have an additive or enhancing effect to antidepressant and/or psychotherapeutic treatment.^[5]

tDCS is generally well tolerated. Reddening of the skin, heat, itching, burning, and tingling sensations at the site of stimulation are the most common reported events in more than 50% of patients.^[6]
Headaches, brighter or illuminated vision, blurred vision, ringing in the ears, fatigue, nausea, mild euphoria, disorientation, insomnia, reduced concentration, and anxiety have also been reported but at low rates
- There is also typically minimal difference between active and sham stimulation which suggests the possibility of a nocebo effect.
There are no studies examining safety and tolerability over long-term use.

Neurostimulation in the Treatment of Major Depressive Disorder

Milev, R. V. et al. (2016). Canadian Network for Mood and Anxiety Treatments (CANMAT) 2016 clinical guidelines for the management of adults with major depressive disorder: section 4. Neurostimulation treatments. The Canadian Journal of Psychiatry, 61(9), 561-575.

Neurostimulation	Overall Recommendation	Acute Efficacy	Maintenance Efficacy	Safety and Tolerability
rTMS	• First line (for patients who have failed at least 1 antidepressant)	Level 1	Level 3	Level 1
ECT	• Second line • First line in some acute clinical situations	Level 1	Level 1	Level 1
tDCS	• Third line	Level 2	Level 3	Level 2
Vagal Nerve Stimulation (VNS)	• Third line	Level 3	Level 2	Level 2
DBS	• Investigational	Level 3	Level 3	Level 3
MST	• Investigational	Level 3	Not known	Level 3