1 Department of Psychology, Concordia University, Montreal, QC, Canada. jake.shenker@gmail.com.
2 BRAMS: International Laboratory for Brain, Music, and Sound Research, Montreal, QC, Canada. jake.shenker@gmail.com.
3 Department of Psychology, Concordia University, Montreal, QC, Canada.
4 Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
5 Brain Imaging Centre, Douglas Research Centre, Montreal, QC, Canada.
6 BRAMS: International Laboratory for Brain, Music, and Sound Research, Montreal, QC, Canada.
7 Cognitive Neuroscience Unit, Montreal Neurological Institute, McGill University, Montreal, QC, Canada.

Adult abilities in complex cognitive domains such as music appear to depend critically on the age at which training or experience begins, and relevant experience has greater long-term effects during periods of peak maturational change. Previous work has shown that early trained musicians (ET; < age 7) out-perform later-trained musicians (LT; > age 7) on tests of musical skill, and also have larger volumes of the ventral premotor cortex (vPMC) and smaller volumes of the cerebellum. These cortico-cerebellar networks mature and function in relation to one another, suggesting that early training may promote coordinated developmental plasticity. To test this hypothesis, we examined structural covariation between cerebellar volume and cortical thickness (CT) in sensorimotor regions in ET and LT musicians and non-musicians (NMs). Results show that ETs have smaller volumes in cerebellar lobules connected to sensorimotor cortices, while both musician groups had greater cortical thickness in right pre-supplementary motor area (SMA) and right PMC compared to NMs. Importantly, early musical training had a specific effect on structural covariance between the cerebellum and cortex: NMs showed negative correlations between left lobule VI and right pre-SMA and PMC, but this relationship was reduced in ET musicians. ETs instead showed a significant negative correlation between vermal IV and right pre-SMA and dPMC. Together, these results suggest that early musical training has differential impacts on the maturation of cortico-cerebellar networks important for optimizing sensorimotor performance. This conclusion is consistent with the hypothesis that connected brain regions interact during development to reciprocally influence brain and behavioral maturation.