Executive function deficits are among the most frequent sequela of very preterm birth but the underlying neuronal mechanisms are not yet fully understood. This thesis contributes to a better understanding by adopting a multimodal approach: Neurodevelopmental assessments were combined with quantitative magnetic resonance imaging (MRI) assessing brain structure and high-density electroencephalography (EEG) assessing brain function to map executive functions in children and adolescents born very preterm. The results show that even those individuals born very preterm with normal intellectual abilities may experience executive function deficits if the demands placed on their abilities are high. Smaller volumes of subcortical brain regions, particularly of the thalamus, were found to be related to poorer working memory abilities, one of the key executive processes. Applying high-density EEG during sleep revealed that individuals born very preterm express higher sleep slow wave activity over brain regions associated with executive processes compared to term-born peers. As sleep slow waves are thought to reflect the synchronized oscillatory activity of the thalamocortical system, these findings contribute further to the overall finding of this thesis: The thalamocortical system appears to be crucially involved in executive processes and the multimodal assessment of its structural and functional integrity provides novel insight into the long-term consequences of very preterm birth.