Table 13.

Reported limitations

Therapeutic application	Article	Limitations
Stroke rehabilitation	[25]	(1) Small number of enrolled patients. (2) There was no comparison between cortical and subcortical lesions
	[30]	(1) Small sample of mildly impaired stroke patients. (2) All subacute stroke patients were in a period of spontaneous recovery. (3) There was no comparison between cortical and subcortical lesions. (4) Lack of sham stimulation or multiple mode simulation of tDCS
	[31]	The small sample size could have influenced the absence of group differences, since the sample size is related to the power analysis
	[29]	(1) It was not possible to obtain solid evidence for any functional change in the brain using functional MRI or PET. (2) Most patients had spontaneous recovery of motor function. (3) The small sample size, lack of multiple center involvement, and short-term evaluation and follow-up were factors increasing the ambiguity in terms of long-term therapeutic effect and experiment consistency
	[28]	(1) The small sample size.(2) There was no control condition.(3) Difficulty at identifying eligible subjects
	[33]	Future studies are needed to determine whether the observed changes were promoted by the intervention itself or by a change of intervention
	[32]	(1) Small sample. (2) Only single-blinded. (3) Patients have additional rehabilitation therapies in the medical center
Phobia and PTSD	[34]	(1) There was only one NIBS session. (2) Although the study was successfully blinded, some participants reported sensations during active iTBS. (3) Baseline measurements of HR, HRV and SCL were recorded after iTBS only due to the complexity of study design
	[35]	(1) The delay (due to the study design) between the use of iTBS and the measurement with fNIRS may attenuate the effects of iTBS. (2) The use of iTBS may had induced counteracting effects: better cognitive control (thus better emotion regulation), and diminished feeling of presence in the VE
	[36]	The small sample size
Cerebral palsy	[37]	N/R
	[26]	N/R
	[38]	(1) The small sample size. (2) The lack of exploration of different electrode positions and tDCS protocols
Neuropathic pain	[39]	N/R
	[40]	(1) There was no control condition for the tDCS-VR intervention group. (2) The study was not blinded for patients. (3) The intervention always included both tDCS and VR, so that it was not possible to discriminate between the effects on pain of each separately
Multiple sclerosis	[41]	(1) Sample size. (2) Patient reported itching sensation after VR-tDCS session

N/R not reported