tES (tDCS / tACS / tRNS)

Non-invasive write · writes

Transcranial electrical stimulation (tES) passes a weak electric current between electrodes on the scalp. In tDCS the current is constant, and at 1–2 mA it sets up a cortical field of up to about 0.4–0.8 V/m that shifts neurons' membrane potential below firing threshold, changing their excitability. tACS uses a sinusoidal current aimed at brain oscillations, and tRNS a random-noise current. In 2025 the US Food and Drug Administration approved a home tDCS headset for depression.

Spatial resolution

54.5 mm (focal extent)

Temporal resolution

2.5 ms (inter-pulse interval)

Field of view

3.28–54.2 cm³ (suprathreshold volume)

Reads

n/a

Writes

scalp-applied electric current (direct, alternating or random noise); intracranial electric field; neuronal membrane potential; brain oscillations

Destructive?

non-destructive

Prerequisites

none beyond ordinary participation

Theoretical spatial resolution

14.5 mm (suprathreshold extent)

Theoretical field of view

1.12–1.23 L (reachable envelope)

Description

Transcranial electrical stimulation (tES) is a non-invasive brain stimulation technique that passes a weak electric current between two or more scalp electrodes to modulate brain activity. Much of the current is shunted through the scalp. The rest sets up a weak electric field in the brain. For 1 mA of tDCS or tACS over the human visual cortex, a computational model gives a cortical field of 0.417 V/m, assuming a gray matter conductivity of 0.24 S/m. The waveform defines the variants. tDCS delivers a constant direct current, for example 1–2 mA, and its effect depends on the direction of current flow. At 1–2 mA it produces cortical fields up to about 0.4–0.8 V/m that polarize neuronal membranes below firing threshold. This modulates excitability, spontaneous firing and plasticity without directly evoking spikes. tACS delivers a sinusoidal, biphasic current through the same basic electrode montage. On average it does not shift the membrane potential, and its aim is to influence brain oscillations. tRNS applies a random electrical oscillation spectrum. Over the motor cortex, its 100–640 Hz components appear responsible for an increase in excitability. It is described as free of the current-direction sensitivity of tDCS. On 8 December 2025 the US Food and Drug Administration approved a tDCS headset designed for home use, restricted to prescription, to treat moderate to severe major depressive disorder in adults. A treatment study in Alzheimer disease, registered as completed with 5 participants, planned 40 Hz tACS for 1 hour in 20 sessions.

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