Since version 2.0, the TI Planning tool (TIP) supports three TI modes, which now in TIP v3.0 are available for the two flavors (non-personalized and personalized):
- classic TI: two sinusoidal high-frequency currents with slight frequency difference are applied, resulting in a high-frequency carrier, modulated at the low difference frequency;
- multi-channel TI: up to eight channels are supported, the frequency, amplitude, and relative phases of which can be freely chosen (in accordance with the hardware capabilities of the TIBS device; TI Solutions AG, Switzerland);
- phase-modulation TI: up to eight channels are supported, which have the same frequency, but individual phase modulation, enabling the generation of complex modulation and pulsation schemes (in accordance with the hardware capabilities of the TIBS device; TI Solutions AG, Switzerland).
Having more than two channels permits to 1) improve focality and stimulation selectivity (and even achieve multifocal stimulation) and 2) distribute the currents over larger scalp surfaces and therefore reduce current densities and the risk of associated confounding sensations.
Having more than two channels, combined with precise control over the immediate channel phase, also opens exciting possibilities with regard to activity or state synchronized stimulation, as well as pulsed and burst stimulation and complex modulation shapes. The latter are important with regard to improving stimulation efficiency and the selective stimulation of neural subpopulations associate with specific brain activities or function.
Fully automatic exposure condition optimization is currently only available for classic TI. For multi-channel TI and phase-modulation TI, similar functionality is planned for a forthcoming TIP release.