White Matter Plasticity in Dancers and Musicians

This dissertation examined training-related brain plasticity by comparing white matter (WM) structure between dancers and musicians and relating the structural changes to dance and music abilities. We focused on the primary motor pathways, to identify potential structural differences between whole-body dance training and specific-effector music training. To this purpose, highly trained dancers and musicians, matched for years of training, were tested on a novel dance imitation task, melody discrimination, and rhythm reproduction. Participants were scanned using magnetic resonance imaging (MRI). WM was analyzed at a whole-brain level in Study 1, using diffusion tensor imaging (DTI). Study 2 used probabilistic tractography to examine the descending motor pathways from the hand, leg, trunk and head regions. In Study 1, dancers showed increased diffusivity and reduced anisotropy in comparison to musicians in regions including the descending motor pathways, the superior longitudinal fasciculus and the corpus callosum, predominantly in the right hemisphere. Consistent with this, in Study 2, dancers had increased diffusivity and greater volume in all portions of the right descending motor pathways, whereas musicians had increased anisotropy, especially in the right hand and trunk/arm tracts. Importantly, in both studies, DTI metrics were positively related with dance and negatively with melody performance. In Study 2, DTI metrics also were negatively associated with age of training start, indicating a direct relation between the structural changes observed and training. Our findings indicate that different types of long-term training have distinct effects on brain structure. In particular, dance training, which engages the whole body, appears to enhance connectivity among a broad range of cortical regions, possibly by increasing axonal diameter and the heterogeneity of fiber orientation. In contrast, music training seems to increase the coherence and packing of the connections linked to the trained effector(s). This dissertation is novel in comparing brain structure between two groups of highly trained performers and in examining multiple DTI metrics concurrently. Further, in Study 2, we developed a novel methodology to segregate the motor cortex into regions corresponding to four main body parts, which could be used by other researchers interested in motor connectivity.