MEG Evidence of Concurrent Bilateral and Hemisphere-Specific Developmental Patterns in Auditory Cortex.

Children demonstrate remarkably different temporal characteristics, as well as higher interindividual variability, in the cortical auditory responses as compared with adults. The detailed dynamics at the level of underlying current generators are, however, not established. We used magnetoencephalography (MEG) to explore the age-related differences in the cortical currents probed by simple auditory stimuli across age groups in children between 6 and 13.5 years and adults, with a specific focus on the time course of hemispheric differences. Two concurrent but independent changes by age were evident. First, linearly increasing adoption of early transient automatic processing appeared developmentally earlier in the right than in the left hemisphere, replicating previous findings. Second, enhanced reactivity of the cortex, in bilaterally symmetric manner at > 200 ms, was strongest in the mid to late childhood thus developmentally following an inverted u-curve. Our findings support the idea of increased responsiveness of the sensory cortices in a specific developmental stage, that may underlie sensitive periods for perceptual learning. The delayed emergence of transient responses in left hemisphere may reflect its role in attuning to the rich language input during extended period of development. SUMMARY: Auditory cortex responses to tones show a shift in emphasis from P50m to N100m. N100m emerges earlier in development in the right than in the left hemisphere. Children in mid-childhood show prominent bilateral late reactivity, suggesting a period of heightened sensitivity to stimulation.