What is Transcranial?

Referring to techniques that deliver energy (electrical current, magnetic fields, ultrasound) through the intact skull to stimulate or modulate brain activity without surgical intervention.

What category does Transcranial belong to in BCI?

Transcranial is a Implant Types concept in brain-computer interface science.

Transcranial — BCI Glossary

Transcranial techniques pass energy through the skull to interact with brain tissue non-invasively. Unlike implanted devices that require surgery, transcranial approaches can be applied externally, making them widely accessible for research, therapy, and potential BCI applications. The major transcranial modalities are transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), and transcranial focused ultrasound (tFUS).

Transcranial Magnetic Stimulation (TMS)

TMS uses a rapidly changing magnetic field generated by a coil placed on the scalp to induce electrical currents in underlying cortical tissue. A single TMS pulse can depolarize neurons and evoke motor responses (used for mapping motor cortex and measuring corticospinal excitability). Repetitive TMS (rTMS) can produce lasting changes in cortical excitability and is FDA-cleared for treatment of major depression, OCD, and smoking cessation.

Transcranial Electrical Stimulation

tDCS: Delivers a weak direct current (1-2 mA) between two scalp electrodes, shifting cortical excitability. Anodal stimulation generally increases excitability; cathodal decreases it. Used in rehabilitation research and cognitive enhancement studies.
tACS: Delivers alternating current at specific frequencies to entrain neural oscillations. Investigated for modulating alpha, beta, and gamma rhythms.
Temporal interference (TI): Uses two high-frequency electric fields that interfere at a deep brain target, producing a low-frequency envelope that stimulates deep structures non-invasively.

Transcranial Focused Ultrasound (tFUS)

Focused ultrasound can non-invasively modulate neural activity with millimeter-level spatial precision — far better than electromagnetic approaches. Low-intensity tFUS has been shown to suppress or excite neural activity depending on parameters. It is being investigated as a non-invasive alternative to DBS for deep brain targets.

BCI Relevance

Transcranial stimulation is primarily a write modality — delivering information to the brain rather than reading from it. Combined with EEG-based recording (a read modality), transcranial stimulation could enable non-invasive bidirectional BCIs. However, the spatial resolution and signal quality limitations of both EEG and transcranial stimulation currently limit the practicality of this approach compared to implanted systems.