Neuroanatomical Correlates of Intelligence, Speech and Language in Adolescents Born Preterm.

Abstract

Aims: This thesis sets out to assess the long-term speech, language and intellectual abilities of children born very prematurely (less than 33 weeks' gestational age) – and to investigate the neuroanatomical correlates of any deficits identified. Method: The study participants (n=50, mean age 16 years) consisted of a representative sample that was recruited from a prospective follow-up study at University College Hospital (London). This included children with a wide spectrum of brain injuries (identified at birth) matched with a term-born control group (n=30). An extensive battery of standardised assessments was administered, including measures of expressive and receptive language, vocabulary, speech-motor control and intelligence. All participants underwent neuroimaging, including diffusion-weighted MRI (DWI). Functional MRI was also used to determine hemispheric language lateralisation. Potential neural correlates of intelligence, speech and language were explored using manual tracing, voxel-based morphometry and DWI-tractography of relevant white matter pathways, such as the language-associated arcuate fasciculus and the speech-motor fibres of the corticobulbar tract (CBT). Results: In comparison to controls, the preterm group had a lower mean IQ score and increased incidence of speech and language problems. Conventional MRI showed abnormalities in more than half of the preterm children, most commonly within the periventricular and callosal white matter. Global brain white matter volume was also reduced in the preterm sample and explained a substantial proportion (70%) of the variance in their IQ scores. Problems with oromotor control were found to be associated with specific abnormalities in the posterior limb of the internal capsule (which contains the CBT); and the degree of language impairment was linked to a reduction in the volume of interhemispheric connections between the temporal lobes. Conclusions: This study has shown that preterm birth is associated with persistent changes in global, commissural and periventricular white matter (identifiable in adolescence) and has established robust neuroanatomical correlates of long-term outcomes in general intelligence, speech and language abilities