Investigating the lateralisation and disconnection model of social functioning in Agenesis of the Corpus Callosum using cognitive neuroscience techniques

© 2013 Dr. Alissandra May McIlroyRecent research has begun to characterise the nature of social dysfunction in individuals with agenesis of the corpus callosum (ACC). Typical lateralisation of function coupled with disrupted interhemispheric transfer between the cerebral hemispheres has been proposed to account for the difficulties observed on various socio-emotional tasks in ACC, ranging from basic emotion perception through to higher-level nonliteral language comprehension and social reasoning. It has also been speculated that this laterality and disconnection model applies to social difficulties experienced in everyday life. The key underlying assumptions of the model have not been directly addressed, however. Specifically, the cerebral lateralisation of socio-emotional functions has not been investigated in individuals with ACC, and whilst it is known that interhemispheric transfer capacities are limited by task complexity, transfer of socially relevant information between the left and right hemispheres has not been assessed to date. The present thesis investigated the lateralisation of emotional and non-emotional face processing and language in individuals with ACC as well as the interhemispheric transfer and integration of emotional information. The impact of other factors (extent of ACC, comorbid brain malformations and handedness) on laterality and interhemispheric transfer were also considered. Twenty-two participants with ACC (50% male; 47% right-handed) aged between 8.33 and 22.67 years (M= 12.13 years, SD= 3.28 years) and 16 typically developing controls (50% male; 75% right-handed) aged between 8.00 and 22.50 years (M= 12.64 years, SD= 3.63 years) were recruited through the Royal Children’s Hospital, Melbourne. Participants completed three out-of-scanner computerised tasks (chimeric faces, face matching and face-word matching tasks) and two in-scanner functional magnetic resonance imaging tasks (explicit emotion processing and noun-verb generation tasks). There was convergent evidence for a higher rate of atypical lateralisation of socially relevant functions in ACC. In addition, there was evidence for a reduction (but not elimination) of the capacity for interhemispheric transfer and integration of facial expressions and affective labels in ACC. Only individuals in the partial ACC group were able to match bilaterally presented facial expressions at above chance levels, suggesting some capacity for interhemispheric transfer of facial emotion information in this group, but elimination of this capacity in the complete ACC group. Whilst the results of the interhemispheric transfer experiments largely fit with the propositions of the laterality and disconnection model, the evidence for atypical lateralisation in ACC indicates that the model does not provide a sufficient explanation for social dysfunction in this population. Alternative models that account for individual variability in ACC will be discussed