Figure 1.

Illustration of the experimental design. Each subject underwent two experimental sessions. At the beginning of the session, the subjects first received either a placebo or a nicotine patch. After a 6 h break, baseline (BL) motor-evoked potentials (MEPs) of approximately 1 mV amplitude were recorded by single pulse transcranial magnetic stimulation (TMS) over the motor cortical representational area of the abductor digiti minimi muscle (ADM). One of the four stimulation protocols (anodal transcranial direct current stimulation (tDCS)/cathodal tDCS/paired associative stimulation (PAS)-25/PAS-10) was then applied. After-measurements were made immediately following the stimulation and once every 5 min for the first 30 min, then once every 30 for 120 min for both sessions. In addition, MEPs were also recorded the same evening, next morning, and evening for the nicotine patch sessions.