Transcranial direct current stimulation for psychiatric disorders: evidence and rationale

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that applies low electrical currents to the scalp, modulating neuronal activity and excitability. tDCS can enhance or inhibit cortical function depending on the polarity of the stimulation. Anodal stimulation depolarizes neurons, enhancing excitability, whereas cathodal stimulation hyperpolarizes neurons, reducing excitability. These effects are thought to result from both synaptic and non-synaptic mechanisms, including shifts in the resting membrane potential and potential activation of peripheral nerve endings. These may stimulate brainstem structures such as the locus coeruleus, influencing mood and arousal. In psychiatric disorders, tDCS is found to be promising for modulating abnormal brain activity in conditions such as depression, schizophrenia, obsessive-compulsive disorders, neurocognitive disorders and substance dependence. Conventional tDCS protocols use currents between 1–2 mA, with electrode sizes ranging from 25–35 cm 2 and stimulation durations of 10–30 minutes. Although tDCS is emerging as a potential therapeutic tool for psychiatric disorders, research in vulnerable populations is lacking. Since tDCS is relatively portable, easier to administer and less expensive than other neuromodulation techniques, it also has the potential to become a domiciliary therapeutic option. This review focuses on the basics of tDCS with a focus on evidence-backed protocols and the scope of tDCS in various neuropsychiatric disorders, which will guide clinicians in choosing appropriate targeted brain stimulation strategies in their clinical practice.