Comparisons of event-related potentials after repetitive transcranial magnetic stimulation

Effects of repetitive transcranial magnetic stimulation (rTMS) on the human cognitive process were investigated by examining auditory event-related po tentials (ERPs) in 15 healthy subjects. Two rTMS trains were delivered over the left frontal area, with 30 pulses in each train. ERPs were recorded at 14 electrode sites on the scalp using a typical oddball protocol before an d after rTMS. Tone stimuli (20% target and 80% standard) were delivered thr ough earphones. Latency and amplitude of N-100, P-200, N-200 and P-300 were measured and compared during the study. To observe information flow betwee n two electrode sites, directed coherence (DCOH) was calculated on the ERPs . Our results show that the effect of rTMS differs in the various ERPs comp onents (P < 0.001). The latency of P-300 significantly increased after stim ulation, and the increase was more obvious in the frontal (18.6 ms) and cen tral (15.8 ms) areas. The latency of P-200 decreased in all areas. The ampl itude of component N-100 in the frontal and central areas decreased after r TMS. DCOH from the central area to the temporal area and DCOH from the pari etal area to the temporal area were significantly higher than the DCOH betw een other areas (P < 0.01), and these properties were not affected by rTMS (P > 0.05). Information flow was driven from the frontal area to the pariet al area after stimulation. Our results suggest that rTMS can suppress cogni tive activities, showing an inhibitory effect on neurophysiological process es in the human brain. Since the temporal area is located at the terminus o f the propagation pathways, it plays important roles in processing informat ion in cognitive activities.