Table 2.

Main clinical outcomes after transcranial electric stimulation.

Model	Stroke stage	Technique	Types of protocol	Reported results	Clinical outcome	Possible signalling pathway	Data
Clinical data	Healthy volunteers	A-tDCS and C-tDCS	Continuous currents for 4 s (excitability shifts during tDCS), 5 (short-lasting excitability shifts), 9 (C-tDCS), or 11 min (A-tDCS), with an intensity of 1.0 mA. A-tDCS was repeated 20 min after the first stimulation	A-tDCS can modulate GABAergic inhibition	Anodal stimulation enhances excitability, cathodal stimulation reduces it enhancement of neurotransmitter metabolism	Might be due to influences of remote cortical or subcortical structures	Nitsche et al., [103]
			A-tDCS 1 mA current, with a ramp up time of 10 s, held at 1 mA for 10 min, and then ramped down over 10 s. For sham stimulation, the current was ramped up over 10 s and then immediately switched off	A-tDCS caused locally reduced GABA, C-tDCS caused reduced glutamatergic neuronal activity with a highly correlated reduction in GABA	A-tDCS - decreased metabolism, C-tDCS - intensive neurotransmitter metabolism	Reduced activity of GAD-67, the rate-limiting enzyme in the major metabolic pathway for GABA synthesis	Stagg et al., [104]
	Acute	C-tDCS	A current of 1.5 mA or sham current delivered hourly for 20 min each, over a period of 6 hours and 20 min; C-tDCS started before completion of recanalization procedure in all patients	Reduced infarct volume of stroke patients receiving reperfusion therapy	Better motor improvement and more functional independence at 3 months post stroke; no major adverse effects (death or neurological deterioration); no statistical difference between the treated and sham groups	No data	Pruvost-Robieux et al., [107]
		C-tDCS, A-tDCS and bilateral tDCS	Each patient received 10 sessions (5 consecutive days for 2 weeks) of real or sham stimulation at 2 mA intensity and current density equivalent to 0.05 A/m2. For sham stimulation, the current was ramped up over 30 seconds and then turned off	No data	Significant motor recovery sustained at least three months beyond the intervention; decreased risk of falls; only in the bilateral stimulation group was reported an increase in the lower limb's motor skills		Andrade et al., [38]
		C-tDCS vs. A-tDCS	A current of 2 mA for 25 min daily for 6 consecutive days over the motor cortex hand area	A-tDCS over the affected hemisphere may be as effective as C-tDCS on the unaffected hemisphere to enhance recovery after acute ischemic stroke	Clinical improvements not only in the upper limb but also in the lower limb on the affected side		Khedr et al., [106]
	Chronic	A-tDCS	Current (1 mA) remained on for 20 min in the tDCS session and for up to 30 s in the sham session	The effect outlasted the stimulation period	Beneficial influence on skilled motor functions of the paretic hand in patients suffering from chronic stroke; significant functional improvement of the paretic hand compared with motor therapy alone		Hummel et al., [105]
			Applied with the anode positioned over the ipsilesional M1 and the cathode over the contralateral supraorbital region for 20 min (1 mA); sham current applied for only 1 min after which it was slowly tapered down to 0 for the remainder 19 min	Effects maintained 1 and 6 days after the completion of the training	No complications were reported; improved motor performance compared with motor practice or with practice combined with either intervention alone;		Celnik et al., [126]
		C-tDCS and A-tDCS	30 min of 1.5 mA direct current with the anode placed over the ipsilesional and the cathode over the contralesional motor cortex	Functional reorganization of the ipsilesional motor cortex	No adverse effects were observed; improved motor functions		Lindenberg et al., [36]
			Single session of 20 min with 1.5 mA current. The anode was over the M1 contralateral to the paretic limb and the cathode over the M1 contralateral to the nonparetic limb (current density 0.06 mA/cm2)	Effects maintained for 3 weeks	Improved retention of gains in motor function	Might be modulated through intracortical inhibitory pathways	Goodwill et al., [127]

A-tDCS: anodal transcranial direct current stimulation; C-tDCS: cathodal transcranial direct current stimulation; GABA: γ-aminobutyric acid; GAD-67: glutamate decarboxylase 67; tDCS: transcranial direct current stimulation.