Table 2.

Effects of tDCS on fear memory in animal models.

References	Study type	Subjects and groups	Target area	Target electrode position	Return electrode position	Stimulation polarity	Size of target and return electrodes	Online/offline stimulation	Intensity (mA)	Duration (minutes)	Drug/doses	CS/UCS	Outcome measures	Outcome
Manteghi et al. (2017)	RCT, placebo and sham controlled	64 male NMRI mice, 8 groups	Prefrontal region(right)	1 mm anterior and 1 mm right to the Bregma	Chest	Anodal	3.5 mm2, 9.5 cm2	Offline, 24 h before conditioning	0.2	20	ACPA/0.01, 0.05, and 0.1 mg/kg	Tone/foot shock	- Freezing duration and latency - Grooming and rearing duration	- tDCS improved short-term contextual fear memory (0.01 and 0.05 doses of ACPA) and long-term contextual and auditory fear memory formation (all doses of ACPA)
Abbasi et al. (2017)	RCT, sham controlled	41 male NMRI mice, 5 groups	Prefrontal region(left)	1 mm anterior and 1 mm left to the Bregma	Chest	Anodal, cathodal	3.5 mm2, 9.5 cm2	Offline, immediately before fear conditioning	0.2	20 and 30	No drugs	Tone/foot shock	Freezing duration and latency	- tDCS impaired acquisition of contextual and cued fear memory (Contextual: 20 and 30 min of anodal, 30 min cathodal; Cued: 20 min anodal, 30 min cathodal)
Nasehi et al. (2017b)	RCT, placebo and sham controlled	120 male NMRI mice, 9 groups	Prefrontal region (right)	1 mm anterior and 1 mm right to the Bregma	Chest	Anodal, cathodal	3.5 mm2, 9.5 cm2	Offline, 1 day before/immediately after fear conditioning	0.2	20	Propranolol/0.1 mg/kg	Tone/foot shock	Freezing duration and latency	- Post-training cathodal stimulation itself facilitated contextual and auditory fear memory retrieval - Pre-training application of cathodal tDCS combined with pre- or post- training propranolol restored auditory fear memory retrieval - Pre- and post-cathodal tDCS in combination with pre-training propanolol increased fear memory retrieval and combined with post-training propanolol increased contextual fear memory - Pre- or post-training anodal tDCS in combination with pre-training propranolol increased contextual and reversed auditory fear memory retrieval - Pre-training anodal combined with post-training propranolol increased contextual fear memory retrieval
Nasehi et al. (2017a)	RCT, placebo and sham controlled	120 male NMRI mice, 9 groups	Prefrontal cortex (left)	1 mm anterior and 1 mm left to the Bregma	Chest	Anodal, cathodal	3.5 mm2, 9.5 cm2	Offline, 1 day before/immediately after fear conditioning	0.2	20	Propranolol/0.1 mg/kg	Tone/foot shock	Freezing duration and latency	- Pre-training cathodaltDCS itself increased contextual fear memory retrieval - Pre- and post-training cathodal tDCS in combination with propanolol pre-training increased fear memory retrieval - Pre- and post-training cathodal tDCSwith post-training propanolol increased contextual fear memory - Pre- and post-training anodal tDCS with pre-training propanolol increased contextual memory retrieval - Pre-training anodal tDCS with pre-training propranolol increased auditory fear memory retrieval