Understanding basal ganglia and thalamic development in very preterm infants

Very preterm (VP) infants who are born at less than 32 weeks’ completed gestation are at an increased risk for poorer long-term cognitive, motor and behavioural outcomes, compared with their term-born peers. The basal ganglia (caudate nucleus, pallidum, putamen, and nucleus accumbens) and thalamus are deep grey matter structures that are known to modulate the functional outcomes that are observed to be impaired in those born VP. Additional to this, there is evidence that these deep grey matter structures are in active development during the VP period. Using magnetic resonance imaging (MRI), the macrostructure and microstructure of the basal ganglia and thalamus can be examined. The aims of this thesis were to investigate (1) individual basal ganglia nuclei and thalamic volume differences between VP and term-born infants at term-equivalent age, in relation to neurodevelopmental outcomes assessed at 7 years; (2) individual basal ganglia and thalamic volume differences between VP and term-born children at 7 years of age, as well as their volumetric growth differences from term-equivalent to 7 years of age, in relation to neurodevelopmental outcomes assessed at 7 years; (3) corticostriatal and thalamocortical tract connectivity differences between VP and term-born children at 7 years of age, in relation to neurodevelopmental outcomes assessed at 7 years. Two hundred and twenty-four VP infants (<30 weeks’ gestational age and/or <1250g birth weight) and 46 term-born infants (37-42 weeks’ gestational age and ≥2500g birth weight) were recruited at birth and underwent brain MRI at term-equivalent age (target scan period: 38-42 weeks’ gestational age, median scan age: 40 weeks’ gestational age). Of these, 159 VP children and 36 controls underwent both neuropsychological assessment and brain MRI in a 7-year follow-up. Individual basal ganglia nuclei and thalamic volumes were obtained through automatic segmentation of the structural images obtained at term-equivalent and 7-year