Maturation of the Brain ’ s Default Mode with Spontaneous Neuromagnetic Signals

Ross, Kakigi, Pantev, & Trainor, 2006), has shown that the evoked (non-oscillatory) brain response in children matures differently according to the sound-type (musical and non-musical) and child's experience in Suzuki music lessons.The current study retrospectively analyzed this data and examined ERS and ERD in terms of differences between stimulus processing and its possible interactions with hemispheric asymmetry, experience, and maturation. Twelve children aged four to six years passively listened to a violin tone and a noise-burst stimulus in total four MEG recording sessions over the course of one year. Time-frequency analysis using Wavelet Transform was applied to single-trials of source waveforms observed from left and right auditory cortices. The results show that bet ERS (13-30 Hz) lasted only for the short 100 ms period after stimulus onset, followed by prominent alpha ERD clearly dissociated between the upper (12 Hz) and lower (8 Hz) range in both left and right auditory cortices for both stimuli. The time courses of the alpha ERD (onset around 300 ms, peak at 500 ms, offset after 1500 ms) were similar to those previously found for older children and adults with auditory memory-related tasks. For the violin tone only, the ERD lasted longer in the upper than the lower alpha band. The findings suggest that alpha ERD indexes auditory stimulus processing in children without specific cognitive task requirement and maturational advantage in left hemisphere.