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Repetitive transcranial magnetic stimulation (rTMS) is a powerful, noninvasive tool for investigating cortical physiologic functions in the brain. However, EEG spectral analysis has not been investigated extensively in rTMS study. The authors investigated the influence of rTMS on the EEG power spectrum by stimulating the left frontal cortex in 32 healthy subjects. Stimulation parameters were a 10-Hz frequency, a 3-second duration, and a 100% motor threshold. The data showed that rTMS increased the peak frequency of EEG across the scalp within 2 minutes after stimulation, whereas the value decreased at 3 to 4 minutes. The mean absolute powers within 3 minutes after rTMS did not differ from those estimated before rTMS, but increased uniformly at 4 to 5 minutes. The spectra did not change after sham stimulation. These results indicate that rTMS can influence cortical activities significantly by increasing the frequency and amplitude of EEG, and is a useful tool for helping us understand brain functions.

Maturation of auditory perceptual and discrimination process within the first two years of life is investigated in healthy infants by examining event-related potentials (ERPs). High-density EEG signals were recorded from the scalp monthly between 3 and 24 months of age. Two types of stimuli (100 vs. 100 Hz for standard stimuli; 100 vs. 300 Hz for deviant stimuli; occurrence rate: 85:15%) were presented using an oddball paradigm. Latencies and amplitudes were compared across development. The results showed that latencies of P 150 , N 250 , P 350 , and N 450 components gradually decreased with increasing age. Amplitudes of the N 250 and P 350 components gradually increased and reached the maximum at 9 months, and then gradually decreased with the increase of age. Mismatch negativity was not obvious at 3 months of age, but was seen at 4-5 months and became robust after 6 months. Robust late positivity was recorded at all ages. These mismatch responses were noticeable in the frontal, central, and parietal areas, and the maximal MMN amplitude distribution gradually moved from the parietal area to the frontal area across the age range. Two important periods-one around 6 months and the other around 9 months are suggested in the maturation of auditory central system. Dynamical changes in the underlying source strengths and orientations may be principal contributors to ERP morphological changes in infants within the first 24 months.

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