Low-Intensity Transcranial Current Stimulation in Psychiatry

Abstract

Neurostimulation is rapidly emerging as an important treatment modality for psychiatric disorders. One of the fastest-growing and least-regulated approaches to noninvasive therapeutic stimulation involves the application of weak electrical currents. Widespread enthusiasm for low-intensity transcranial electrical current stimulation (tCS) is reflected by the recent surge in direct-to-consumer device marketing, do-it-yourself enthusiasm, and an escalating number of clinical trials. In the wake of this rapid growth, clinicians may lack sufficient information about tCS to inform their clinical practices. Interpretation of tCS clinical trial data is aided by familiarity with basic neurophysiological principles, potential mechanisms of action of tCS, and the complicated regulatory history governing tCS devices. A growing literature includes randomized controlled trials of tCS for major depression, schizophrenia, cognitive disorders, and substance use disorders. The relative ease of use and abundant access to tCS may represent a broad-reaching and important advance for future mental health care. Evidence supports application of one type of tCS, transcranial direct current stimulation (tDCS), for major depression. However, tDCS devices do not have regulatory approval for treating medical disorders, evidence is largely inconclusive for other therapeutic areas, and their use is associated with some physical and psychiatric risks. One unexpected finding to arise from this review is that the use of cranial electrotherapy stimulation devices-the only category of tCS devices cleared for use in psychiatric disorders-is supported by low-quality evidence.

Keywords: Antidepressants; ECT; Transcranial Electrical Current Stimulation.

Figure 1A. Sub- and Suprathreshold Energy Input on Neuronal Action Potentials

Subthreshold membrane fluctuations are not sufficient to generate an action potential (left). However, if intrinsic fluctuations in a neuron’s membrane voltage move it closer to its threshold, application of an inherently subthreshold input, such as tCS, can trigger an action potential (right). Dashed line indicates threshold.

Figure 1B. Model of Anode vs. Cathode Stimulation

Schematized representation of anode and cathode stimulation on neuron resting potentials. Placement of the anode over a brain region leads a depolarization that increases the likelihood of neuronal firing in the cell body (left). In contrast, placement of the cathode leads to hyperpolarization, which decreases the likelihood of neuronal firing (right).