Table 1.

Stimulus conditions for all experiments

Condition	P	S1	S2	S2*
A			MEP1.5mV
B		0.9 × AMT	MEP1.5mV
C	3 × PT		MEP1.5mV
D				cMEP1.5mV
E		0.9 × AMT		cMEP1.5mV
F	3 × PT			cMEP1.5mV
G	3 × PT	0.9 × AMT		cMEP1.5mV

P, electrical pulse to the right ulnar nerve; 3 × PT, three times perceptual threshold; S1, conditioning magnetic stimulus to left motor cortex; AMT, active motor threshold; S2, test magnetic stimulus to left motor cortex; MEP_1.5mV, unconditioned test motor-evoked potential of 1.5 mV in peak-to-peak amplitude; S2*, test stimulus to left motor cortex of adjusted intensity; cMEP_1.5mV, conditioned test motor-evoked potential (by P or S1) of 1.5 mV in peak-to-peak amplitude. In Experiment 1, the interstimulus interval between P and S2 (or S2*) was fixed at N₂₀+ 2 ms, while the interval between S1 and S2 (or S2*) varied (1.0, 1.5, 2.1, 2.7 and 3.0 ms). In Experiment 2, the interstimulus interval between P and S2 (or S2*) varied (N₂₀+ 2 ms, N₂₀+ 4.1 ms), while the interval between S1 and S2 (or S2*) was fixed at 2.1 ms. In Experiment 3, the interstimulus interval between S1 and S2 (or S2*) was 2.1 ms, and that between P and S2 (or S2*) was N₂₀+ 2 ms.