When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
A body of current evidence suggests that there is a sensitive period for musical training: people who begin training before the age of seven show better performance on tests of musical skill, and also show differences in brain structure – especially in motor cortical and cerebellar regions – compared with those who start later. In two studies, we investigated distributed patterns of structural differences between early-trained (ET) and late-trained (LT) musicians. First, we examined structural covariation between cerebellar volume and cortical thickness (CT) in sensorimotor regions in ET and LT musicians and non-musicians (NMs). We found that 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. In the second study, we used support vector machine models – a subtype of supervised machine learning – to investigate cortico-cerebellar structural covariation and to better understand the age boundaries of the sensitive period for early musicianship. Our model identified a combination of 19 regions, including 12 cerebellar and 7 sensorimotor regions, that accurately identified ET and LT musicians with high sensitivity and specificity. Critically, this model – which defined ET musicians as those who began their training before the age of 7 – outperformed all other models in which age of start was earlier or later (between ages 5-10). Our model’s ability to accurately classify ET and LT musicians provides additional evidence that musical training before age 7 affects cortico-cerebellar structure in adulthood, and is consistent with the hypothesis that connected brain regions interact during development to reciprocally influence brain and behavioural maturation. Together, these results suggest that early musical training has differential impacts on the maturation of cortico-cerebellar networks important for optimizing sensorimotor performance. This work enriches our understanding of how experience-dependent plasticity is affected by early musical training, providing a more nuanced understanding of the interrelated nature of brain development.