TABLE 7.

Studies and experimental characteristics of tES literature for PD.

Authors	Subjects	Stimulation parameters				Neuroimaging		Conclusion
		Type	Current	Duration	Location	Type	Feature
Del Felice et al., 2019	15	tACS++tRNS	4 or 30 Hz, 1 to 2 mA, 30 min	5 sessions per week for two weeks	Anode: The location of power spectral difference was detected, cathode: ipsilateral mastoid	EEG	Power spectral in delta (1–4 Hz), theta band (4.5–7.5 Hz), alpha1 (8–10 Hz), alpha2 (10.5–12.5 Hz), beta (13—0 Hz)	Individualized tACS in PD improves motor and cognitive performance. These changes are associated with a reduction of excessive fast EEG oscillations.
Beretta et al., 2020	24	tDCS	1 and 2 mA, 20 min	3 sessions 2 weeks apart	Anode: primary motor cortex, cathode: contralateral supraorbital region	fNIRS	The concentration changes of HbO	tDCS over M1 improved the postural response to external perturbation in PD, with better response observed for 2 mA compared with 1 mA, and was inefficient in modifying the habituation of perturbation
Schoellmann et al., 2019	21	tDCS	1 mA, 20 min	1 session	Anode: left sensorimotor (C3), cathode: right frontal area (FP2).	EEG	Frequency domain spectrum and coherence	tDCS improved PD motor symptoms. Neurophysiological features indicated amotor-task-specific modulation of activityand coherence from 22 to 27 Hz after ‘verum’stimulation in PD.