Poster A9, Tuesday, August 20, 2019, 10:15 am – 12:00 pm, Restaurant Hall
Inconsistency in lateralisation of language functions: a risk factor for language impairment?
Abigail Bradshaw1, Zoe Woodhead1, Paul Thompson1, Dorothy Bishop1;1University of Oxford
Introduction: Language laterality (the greater involvement of the left hemisphere in language processing than the right) is generally assumed to be beneficial for language functioning. Disruption to language lateralisation has long been proposed as a cause of developmental language impairments; however this has so far only been investigated by looking for laterality strength differences between groups on a single task. Alternatively, it is possible that the relevance of laterality to language functioning may relate more to whether different language functions show common lateralisation; inconsistent laterality across language sub-processes may represent a less efficient network that places greater demands on interhemispheric integration. This study tested the hypothesis that inconsistent lateralisation across different language functions would be associated with poorer language abilities. This was tested using an ultrasound technique (functional transcranial Doppler ultrasound, fTCD) with a large sample of individuals who varied in their language abilities. Methods: This study was pre-registered on Open Science Framework (https://osf.io/fvhxq/), and a power calculation used to determine sample size. 104 adult participants were tested in this study, 67 of which had a developmental disorder affecting language (e.g. dyslexia, dyspraxia, ASD) and 37 of which had no diagnosis relating to language. All participants were tested with a comprehensive language assessment battery and fTCD measurement of laterality for three tasks designed to engage different language sub-processes (sentence generation, phonological decision and semantic decision). The whole sample was divided into those showing consistent and inconsistent lateralisation across our three tasks, and their language scores on our standardised assessments compared by means of a multivariate test. We further explored whether the developmental disorders group demonstrated an increased incidence of inconsistent laterality patterns. Results: We identified 31 participants within our sample who demonstrated inconsistent lateralisation across our tasks; comparison of their language scores to those of the 73 individuals showing consistent lateralisation did not find significant differences on any language measure. However, the developmental disorder group demonstrated an increased incidence of inconsistent lateralisation (representing 26 of the 31 inconsistent participants) and weaker correlations between laterality indices across pairs of tasks. This suggests a higher level of within individual variability in lateralisation for our developmental disorder group. Conclusions: The findings suggest that having inconsistent lateralisation for different language sub-processes is not associated with poorer language skills. However, experience of a developmental disorder may increase the likelihood of having a more distributed organisation of language functions across the hemispheres, potentially reflective of attempts at compensatory reorganisation. This pattern of findings suggests the need to reconsider assumptions about the direction of causality between altered laterality patterns and disrupted development of language skills.
Themes: Disorders: Developmental, Language Production
Method: Functional Imaging