tDCS

Transcranial direct current stimulation (tDCS) is a form of non-invasive brain stimulation that delivers a low-intensity direct current to the scalp through electrodes. It is studied as a tool for altering brain activity with potential therapeutic and cognitive effects, though its efficacy varies by condition and protocol.

The mechanism of tDCS involves subthreshold shifts in neuronal membrane potential caused by the applied current. Anodal stimulation tends to increase cortical excitability, while cathodal stimulation tends to decrease it. After-effects may reflect synaptic plasticity processes, such as NMDA receptor–dependent changes and modulators of neuroplasticity, which can last beyond the stimulation period.

Typical protocol parameters include currents of about 1-2 milliamperes for 10-30 minutes per session. Electrodes are commonly sized to balance focality and comfort, and placement depends on the targeted brain region. Sham tDCS mimics the sensation of stimulation with brief ramping at the start and end to maintain blinding in studies.

Safety and tolerability are generally favorable in healthy individuals and many patient populations. Common side effects are mild and transient, such as tingling, itching, warmth under the electrodes, and headaches. Skin irritation or burns can occur with poor contact. Contraindications include implanted electronic devices in or near the head, a history of seizures, and significant skin lesions; guidance on use in pregnancy and other conditions varies and requires caution.

Evidence for clinical efficacy remains mixed and condition-dependent. Some small-to-moderate effects have been reported for depression, chronic pain, and language or motor rehabilitation after stroke, but results are heterogeneous, with placebo effects and methodological differences complicating interpretation. tDCS is not a substitute for standard medical therapies and is primarily used within research and supervised clinical contexts. Regulation and approval status vary by country, with ongoing research aimed at standardizing protocols and identifying reliable indications.