Croft, L; (2014) Neuroimaging investigations of language to aid paediatric neurosurgical decision making. Doctoral thesis , UCL (University College London).

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Abstract

Childhood onset epilepsy can have a profound effect on cognitive, emotional and behavioural development. As such, early intervention is crucial. Approximately 25-50% of children with epilepsy show resistance to medication however. For these children, neurosurgical intervention may be considered. The decision for surgery is a multi-disciplinary process, including functional Magnetic Resonance Imaging (fMRI) to assess the risk posed by surgery to language. Based on feasibility and behavioural pilot studies, I developed an fMRI task panel optimised for pre-surgical investigations of language in children. This task panel maps different language systems (word retrieval, sentence generation, auditory comprehension and reading comprehension) and localises critical language functions (semantic and syntactic processing). I validated this task panel in healthy children (N=43, 5-16 years). This included assessments of scan quality, comparison of methods for artefact repair, and definition of typical activation patterns. I also piloted the new task panel in a representative sample of children with epilepsy, who were being considered for surgery (N=13, aged 5-16 years). Patient case studies are reported to highlight methodological challenges associated with localisation of critical language regions on an individual basis. Finally, I present experimental analyses which highlight the importance of the ventral system to semantic processing. Activation in this network was reduced in children with epilepsy and predicted language outcome. Further investigation showed prolonged development of specific nodes within this system, supporting multimodal semantic processing (independent of effort and performance accuracy). These regions included ventral occipito-temporal cortex, whose role in semantic processing has so far been underappreciated in the developmental literature. These analyses provide evidence for a core language system, which may be crucial for post-surgical language outcome. The findings from this thesis contribute towards extending and improving the role of fMRI in the surgical decision-making process, with the potential for improving long term outcome. They also contribute to models of typical and atypical language development.

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