Table 2.

Characteristics of included studies.

Reference		Pain group	Control group	Priming	Test
Antal et al. 20083	Experiment 1 Experiment 2	n = 13 patients with migraine with aura (3 M, 33 ± 12 y) n = 13 patients with migraine with aura (3 M, 33 ± 12 y)	n = 13 pain-free controls (3 M, 31 ± 10 y) n = 13 pain-free controls (3 M, 31 ± 10 y)	Excitatory Anodal tDCS 1 mA, 10 minutes Inhibitory Cathodal tDCS 1 mA, 10 minutes	Excitatory* 20 seconds rTMS 100 biphasic pulses at 90% of RMT at a constant rate of 5 Hz Inhibitory* 20 seconds rTMS—100 biphasic pulses at 90% of RMT at a constant rate of 5 Hz
Thapa et al. 201848	Experiment 1 Experiment 2	n = 50 patients with chronic low back pain (26 M, 45 ± 16 y)	n = 25 pain-free controls (13M, 43 ± 17 y)	Single tDCS session—to confirm the excitatory response of anodal tDCS 3-minute rest	Excitatory Anodal tDCS 1 mA, 7 minutes
		n = 50 patients with chronic low back pain (26M, 45 ± 16 y)	n = 25 pain-free controls (13M, 43 ± 17 y)	Excitatory Anodal tDCS 1 mA, 7 minutes 3-minute rest	Excitatory Anodal tDCS 1 mA, 5 minutes
Thapa et al. 202150	Experiment 1	n = 21 healthy individuals (12M, 23 ± 4 y) NGF-induced pain model	n = 21 healthy individuals (12M, 23 ± 4 y) at baseline	Excitatory Anodal tDCS 1 mA, 7 minutes 3-minute rest	Excitatory Anodal tDCS 1 mA, 5 minutes
Wittkopf et al. 202358	Experiment 1	n = 24 healthy individuals (N = 12, 8 M, 25.7 ± 4.6 y) Capsaicin 8% patch-induced	n = 24 healthy individuals (N = 12, 8M, 25.7 ±,2 y) at baseline	Inhibitory Cathodal tDCS 1 mA, 7 minutes 3-minute rest	Inhibitory Cathodal tDCS 1 mA, 5 minutes

^*The direction of effects induced by rTMS depend on preconditioning with tDCS. One study included a session where only the priming session was evaluated.⁴⁹ Although this is not an HP protocol, it was added to the table because it was part of assessing the HP response.