Furthermore unlike Shahin et al who reported

Furthermore, unlike Shahin et al., 2004, who reported an instrument specific enhancement of P2 component, we did not find any difference of P2 component between music and the two comparison groups. This may be related to the difference in musical training methods. While the music children in Shahin et al., 2004; were trained on a specific instrument (piano or violin) based on the Suzuki method, the musical curriculum of our participants was more diverse. It included instrument training (violin), choir, and musicianship and theory skills. The curriculum is specifically designed for group instructions and ensemble performance, not individualized intensive instrumental training. The difference in the time spent on a musical instrument, on an individual basis, versus group musical activities, may have resulted in the lack of P2 effect in our findings. The N1 component, which is the most harpagoside negative auditory ERP component in adult is absent in young children. During development, as age increases, the P1 peak narrows and decreases in amplitude and latency and the N1 peak emerges between ages 8–10, broadens and becomes increasingly negative compared to baseline. This process continues until early adulthood (between ages 18–20), by which time the P1 becomes much smaller in amplitude relative to the robust N1 and, in paradigms where it occurs, typically requiring very short duration auditory stimuli it is commonly named the P50 due to its occurring at approximately 50ms post-stimulus (Cunningham et al., 2000; McArthur and Bishop, 2002; Ponton et al., 2000). N1 peak latency also declines with age. It is important to note that, specifically in children, the morphology of N1 depends critically on inter-stimulus-interval (ISI). Studies using a long ISI, generally longer than 2s, have shown an N1 potential that is sensitive to age whereas the presence of N1 with ISI shorter than 2s is not always reliable. This is the consequence of the high refractory nature of N1 generator in children (Čeponiene et al., 1998; Paetau et al., 1995) which has been shown to decrease with age (Rojas et al., 1998). To account for this phenomenon, we used a long inert-stimulus-interval (2500ms) in our design to assure optimal conditions to detect the presence of N1. The N1 amplitude has been specifically shown to be sensitive to experience-related plasticity—an increase in amplitude has been reported in adults without music training, after short-term training (Pantev and Herholz, 2011). In musicians, N1 amplitude has been shown to be larger, compared to non-musicians, specifically in response to musical stimuli (Habibi et al., 2013; Shahin et al., 2003, 2004). Here we find an increase in N1 amplitude relative to P1 amplitude in children, but only in the music group, over the course of two years of music training. This implies that music training likely is associated with accelerated development of central auditory pathways in children as young as age 8. Similar findings have been recently reported in adolescents with three years of training who show an increase in N1 amplitude relative to P1 amplitude when compared to an age-matched active (participants enrolled in Junior Reserve Officer Training Corp) comparison group (Tierney et al., 2015). Of note, the N1 amplitude has also been shown to be influenced by attention (Picton and Hillyard, 1974). Given that children in the music group are trained to tune their attention to the musical sounds of their instrument and other instruments while practicing and rehearsing, the faster development of N1 in this group may also be related to stimulus specific attentional mechanisms. However, the combination of the changes seen in N1 with those seen in P1, may suggest changes in the maturation of the auditory system. The significant differences obtained in brain measures on the passive pitch perception task between groups was specific to the piano tones, and observed to a smaller but not statistically significant extent to the violin tones and not at all to the pure tones. Given that the participants in the music training group had specific training in violin this was somewhat unexpected. It is important to note, however, that in addition to their specific violin training, music group children participated in music theory, choir and ear training sessions where piano was used as the teaching instrument. Therefore, they were trained to discriminate musical features in particular with piano tones. This stimulus specific training in pitch discrimination may partly explain the lack of difference in the brain processing of pure tones as well as violin tones between the groups. In addition, the spectral complexity of the piano and violin tones, compared to the pure tones likely contributed to the increased number and/or synchronization of neurons coding for the temporal and spectral features of these stimuli and subsequently greater engagement of the auditory pathway, as has been previously demonstrated (Meyer et al., 2006). While the maturation of the P1 component towards an N1 is known to be related to underlying brain morphological development, the effects on the maturation of the P1 to N1 observed to piano tones did not generalize across other stimulus types. This suggests that the observed effects may be related to specific musical stimuli or it is possible that longer periods of training is necessary for such an effect to translate to other auditory stimuli.