. The US was an electrocutaneous stimulus (2 ms duration), which was delivered by a commercial constant current stimulator (DS7A; Digitimer, Welwyn Garden City, England) through surface Sensormedics electrodes (8 mm; SensorMedics Corp,
Yorba Linda, CA) filled with K–Y gel (Johnson & Johnson, New Brunswick, NJ) that were attached to the wrist of
the dominant hand.