Comparisons of event-related potentials after repetitive transcranial magnetic stimulation

Abstracts

Effects of repetitive transcranial magnetic stimulation (rTMS) on the human cognitive process were investigated by examining auditory event-related potentials (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 and after rTMS. Tone stimuli (20 % target and 80 % standard) were delivered through earphones. Latency and amplitude of N₁₀₀, P₂₀₀, N₂₀₀ and P₃₀₀ were measured and compared during the study. To observe information flow between two electrode sites, directed coherence (DCOH) was calculated on the ERPs. Our results show that the effect of rTMS differs in the various ERPs components (P<0.001). The latency of P₃₀₀ significantly increased after stimulation, and the increase was more obvious in the frontal (18.6 ms) and central (15.8 ms) areas. The latency of P₂₀₀decreased in all areas. The amplitude of component N₁₀₀ in the frontal and central areas decreased after rTMS. DCOH from the central area to the temporal area and DCOH from the parietal area to the temporal area were significantly higher than the DCOH between other area (P<0.01), and these properties were not affected by rTMS (P0.05). Information flow was driven from the frontal area after simulation. Our results suggest that rTMS can suppress cognitive activities, showing an inhibitory effect on neurophysiological processes in the human brain. Since the temporal area is located at the terminus of the propagation pathways, it plays important roles in processing information in cognitive activities.