Non-invasive write · writes
Temporal interference stimulation is noninvasive deep-brain electrical stimulation through pairs of scalp electrodes. Each pair passes current at a slightly different kilohertz frequency, too fast for neurons to follow; where the currents overlap deep in the brain they produce a slow beat at the difference between the two frequencies. It writes by delivering this beat, which stimulates neurons and modulates brain rhythms and hippocampal activity, while the fast currents do not make neurons fire. At human field strengths, direct stimulation may be too weak, and the effective intensity remains unclear.
Temporal interference stimulation (TI, or transcranial temporal interference stimulation, tTIS) is noninvasive, steerable deep-brain electrical stimulation. Two or more pairs of scalp electrodes deliver currents at slightly different kilohertz frequencies, each too fast for neurons to follow. Where the fields overlap at depth they interfere and produce an envelope that oscillates at the difference between the carrier frequencies, which lies within the range of neural activity: 1 mA at 1.00 kHz with 1 mA at 1.04 kHz gives a 40 Hz envelope, 2.000 with 2.010 kHz gives 10 Hz, and 9.00 with 9.13 kHz at up to 4 mA peak-to-peak per pair gives 130 Hz. The kilohertz carriers do not themselves recruit firing. The envelope is what acts on tissue: it stimulates neurons, modulating neural oscillations and hippocampal activity. At human field strengths, direct stimulation may be too weak, and the effective intensity remains unclear: in finite-element human head models the hippocampal field reaches only about 0.38 V/m, orders of magnitude below the roughly 100 V/m threshold for direct neuronal activation, and mouse head models reach 383 V/m at 0.776 mA. The kilohertz currents avoid the scalp irritation and pain of conventional noninvasive transcranial electrical stimulation.
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