Table 3.

Comparison of different tACS improvement methods.

Method	Purpose of improvement	Number of stimulation electrodes	Stimulus signal parameters		Stimulus focus	Stimulus intensity	Stimulation artifact	Stimulating effect
			Frequency	Amplitude
HD-tACS	Increase targeting accuracy	4 cathode and 1 anode or 4 anode and 1 cathode	Alpha band and theta band	1–2 mA	Precision	Medium	Medium	Compared with that of traditional tACS, the stimulation intensity of the stimulation area is higher and the stimulation is more focused
Phase-shifted tACS	Change the stimulus phase to affect the connectivity of the stimulated brain region	3	Alpha band and theta band	1–2 mA	General	Medium	Medium	The magnitude of the electric field is different under different stimulation phases, and the electric field intensity under the reversed-phase condition is significantly higher than that under the same phase stimulation condition (2–2.3 times).
AM-tACS	Reduce stimulus artifacts	3	Modulated signal: Alpha band and theta band. Carrier: hundreds of Hz	1–2 mA	General (existing diffuse stimulation)	Medium	Low	Stimulation artifacts can be reduced to the extent that tACS is not applied
Temporally interfering stimulation	Reduce stimulus diffusion and stimulate directly into deep brain areas.	4	Thousands of Hz	100–400 μA (mice)	Precision	Low	Low	Through interference, stimulation can be directly applied to the region of interest to reduce the effect on the cortex, and the focus of the stimulation can be changed by changing the stimulation current rather than the position of the electrode.
Intersectional Short Pulse Stimulation	Enhance focus and increase the amplitude of the stimulus	Multiple pairs of electrodes	1–1,000 Hz	1–7.5 mA	General (existing diffuse stimulation)	High	Medium	The current intensity can be much higher than that of the above stimulation methods while keeping the charge density and sensation on the scalp surface relatively low.