Periodic Reporting for period 4 - CANDICE (CEREBRAL ASYMMETRY: NEW DIRECTIONS IN CORRELATES AND ETIOLOGY)
Période du rapport: 2021-04-01 au 2022-03-31
The goal of the project was 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 were 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.
We were able to show conclusively that language lateralisation is not unitary; rather at least two factors are needed to account for individual variability in language functioning. The first factor seems to largely reflect language generation, and is lateralised to the left hemisphere in most people. Language functions focused more on comprehension and interpretation of language may be strongly lateralised in individuals, but with less of a population bias to one side. There is suggestive evidence that language difficulties are more common in individuals who have different language functions mediated by opposite hemispheres, rather than both being mediated by the left side.
In the course of conducting these studies, we have developed a range of new language assessments, some of which can be administered online, which are useful for pinpointing language deficits in adults as well as children.
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 were 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.
We were able to show conclusively that language lateralisation is not unitary; rather at least two factors are needed to account for individual variability in language functioning. The first factor seems to largely reflect language generation, and is lateralised to the left hemisphere in most people. Language functions focused more on comprehension and interpretation of language may be strongly lateralised in individuals, but with less of a population bias to one side. There is suggestive evidence that language difficulties are more common in individuals who have different language functions mediated by opposite hemispheres, rather than both being mediated by the left side.
In the course of conducting these studies, we have developed a range of new language assessments, some of which can be administered online, which are useful for pinpointing language deficits in adults as well as children.
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 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.