Individual Differences in Rhythm and Grammar Phenotypes and Potential Underlying Genetic Influences

Abstract

This dissertation studied the associations between musical rhythm and grammar phenotypes and underlying polygenic architecture that might influence these traits. These associations were explored using individual approaches and polygenic methods. In doing so, I sought to shed light on the processing mechanisms and the genetic pathways shared by musical rhythm and language. I investigated factors that could be responsible for mediating the relationship between musical rhythm perception and expressive grammar. The findings showed a positive correlation between musical rhythm perception and grammatical skill, converging with recent research on rhythm and grammar skills. Using path modelling, I tested the contribution of potential mediators of the rhythm-grammar skills association and found that this relationship is not mediated via sensitivity to prosody, working memory, nor explained by non-verbal IQ. I also showed that musical rhythm predicted mastery of complex syntax, suggesting a unique leveraging of hierarchical processing between musical rhythm processing and children’s acquisition of complex syntactic structures. I then tested underlying genetic relationships between musical rhythm and language using polygenic methods. I explored the relationship between polygenic score of rhythm and language skills, in typically developing children, and found non-significant correlations. We then tested the predictions of the Atypical Rhythm Risk Hypothesis and used the polygenic score for rhythm to predict the presence of developmental language disorder and broader symptoms of speech and language disorders in a cohort of cases classified from EHRs. We found non-significant associations in both our genetic analyses, and these results are discussed in the dissertation. The results from this dissertation showed that there is a replicable correlation between musical rhythm and grammatical abilities. The underlying biology of this relationship is not yet well understood, and alternate methods are likely to be useful in detecting potential genetic pleiotropy or separate pleiotropy between musical rhythm and language traits. Interpreting the complex biological relationships between these traits could help identify developmental foundations for musical rhythm and grammatical processing. Research geared towards such developmental processes will have far-reaching clinical implications for further research into the identification of disorders that affect language and rhythm skills.