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CEREBRAL ASYMMETRY: NEW DIRECTIONS IN CORRELATES AND ETIOLOGY

Periodic Reporting for period 2 - CANDICE (CEREBRAL ASYMMETRY: NEW DIRECTIONS IN CORRELATES AND ETIOLOGY)

Reporting period: 2018-04-01 to 2019-09-30

The goal of the project is to understand how the two sides of the brain process language, and whether individual differences in functional brain asymmetry have significance for language competence.

This question is of societal importance because language is such a fundamental ability for human achievement and interaction, yet we understand rather little about how the brain mediates this skill, and why some people have language limitations. More distally, there are implications for assessment of cerebral lateralisation in neurosurgical patients, where it is important to evaluate language localisation prior to surgery.

Our overall objectives are to discover whether we can treat language lateralisation as a unitary function, or whether different language skills can be differently lateralised, and whether such variation has any functional significance.
Our previous work suggesting links between language laterality and developmental disorders has not been supported by our most recent analysis of a large dataset. Nevertheless, there are some intriguing results from a study by Abigail Bradshaw who studied adults with dyslexia and related conditions, and did find suggestive evidence of dissociation between lateralisation for different language functions.
We have also been able to show that dissociation between lateralisation for different language functions cannot be explained by poor test-retest reliability. Such dissociation is not a general finding, but does seem to be a feature seen in some left-handers. We are currently collecting further data to test this idea, and hope to gain a larger sample through additional collaborations.
Our predictions regarding genetic interactions as an explanation for language problems in people with sex chromosome trisomies were not supported, but we were pleased to publish our null results as a Registered Report, where the analysis plan was carefully developed and registered, to avoid spurious null results. We are now testing whether copy number variants differ between those with and without sex chromosome trisomies.
We aim by the end of the project to have a clearer picture of the relationship between lateralisation for different components of language, and how dissociations between these relate to both handedness and to language disorders. We will also have developed measures of communication skills that can be administered online and will allow us to document the nature of problems in children with language disorders more comprehensively.
From Bradshaw et al 2017. Image depicting the analysis of language lateralisation in fMRI.