Auditory cortical development charted by transient and 40-Hz steady-state responses in typical children and in Down syndrome

We are charting neocortical development in typical children and in children with Down syndrome (DS) using evoked transient and 40-Hz steady-state fields (SSFs) which localize to the region of A2 and A1 respectively, in the adult brain. Transient responses contrasted between cohorts aged 5–8 and 11–18 years showed declining P1m and increasing N1m amplitude in typical children (RMS N1m/P1m ratio increasing from 0.97 to 5.91 between the age groups), and decreasing P1m and N1m latency. Neither component changed appreciably with age in DS, although P1m latency decreased. SSF amplitude increased by a factor of 2.3 with age in control children and phase coherence by 2.0, pointing to a developmental effect putatively in A1. Neither SSF amplitude nor phase coherence showed a strong developmental trend in DS. Hearing thresholds did not differ between DS and typical children, implicating central rather than peripheral mechanisms underlying group differences.