Delayed Development of Neural Language Organization in Very Preterm Born Children

What risk factors for Developmental Language Disorder can tell us about the neurobiological mechanisms of language development

Language is a complex multidimensional cognitive system that is connected to many neurocognitive capacities. The development of language is therefore strongly intertwined with the development of these capacities and their neurobiological substrates. Consequently, language problems, for example those of children with Developmental Language Disorder (DLD), are explained by a variety of etiological pathways and each of these pathways will be associated with specific risk factors. In this review, we attempt to link previously described factors that may interfere with language development to putative underlying neurobiological mechanisms of language development, hoping to uncover openings for future therapeutical approaches or interventions that can help children to optimally develop their language skills.

Language lateralization in very preterm children: associating dichotic listening to interhemispheric connectivity and language performance

BACKGROUND

Language difficulties of very preterm (VPT) children might be related to weaker cerebral hemispheric lateralization of language. Language lateralization refers to the development of an expert region for language processing in the left hemisphere during the first years of life. Children born VPT might not develop such a dominant left hemisphere for language processing. A dichotic listening task may be a functional task to show the dominance of the left hemisphere during language processing. During this task, different acoustic events are simultaneously presented to both ears. Due to crossing fibers in the brain, right ear stimuli are transferred directly to the left hemisphere, and left ear stimuli are transferred first to the right hemisphere and then, through the corpus callosum (CC), to the left hemisphere. Dichotic listening typically shows a right ear advantage, assuming to reflect left hemispherical language dominance. The CC, in particular the splenium, is associated with auditory processing and is considered important for language lateralization. The objective of this work was to explore whether dichotic listening performance in school-aged VPT children are associated with language performance and interhemispheric connectivity.

METHODS

This is a cross-sectional study of 58 VPT children and 30 full term controls at age 10 years. Language performance and dichotic digit test (DDT) were assessed. In 44 VPT children, additionally diffusion weighted imaging (DWI) was performed using a 3 T MRI scanner. Fractional anisotropy (FA) and mean diffusivity (MD) values of the splenium of the CC were extracted.

RESULTS

Poorer right ear DDT scores were associated with poorer language performance in VPT children only (p = 0.015). Association between right ear DDT scores and MD of the splenium approached the level of significance (p = 0.051).

CONCLUSIONS

These results support the hypothesis that poor language performance in VPT children may be a consequence of weaker lateralized language organization, due to a poorly developed splenium of the CC. Dichotic listening may reflect the level of language lateralization in VPT children.

IMPACT

Poor language performance in VPT children may be a consequence of weaker lateralized language organization, due to a poorly developed splenium of the CC. Dichotic listening performance may reflect the level of language lateralization in VPT children and right ear scores of a dichotic listening task are associated with both the splenium of the corpus callosum and language performance. If our results could be validated in future research, it suggests that poor CC development may indicate VPT children at risk for long-term language problems.

Are multidisciplinary neurodevelopmental profiles of children born very preterm at age 2 relevant to their long-term development? A preliminary study

To identify distinctive multidisciplinary neurodevelopmental profiles of relatively healthy children born very preterm (VPT) and describe the longitudinal course of these profiles up to age 10. At 2 years of corrected age, 84 children born VPT underwent standardized testing for cognitive, language, speech, motor, behavioral, and auditory nerve function. These data were submitted to factor and cluster analysis. Sixty-one of these children underwent cognitive, language, and behavioral assessment again at age 10. Descriptive statistics were used to analyze longitudinal trajectories for each profile. Four neurodevelopmental profiles were identified at age 2. Profile 1 children (n = 22/26%) had excellent cognitive-language-motor function, normal behavioral and auditory nerve function, but showed an unexpected severe decline up to age 10. Profile 2 children (n = 16/19%) had very low behavioral function, low cognitive-language-motor function, and accelerated auditory nerve function. Their scores remained low up until age 10. Profile 3 children (n = 17/20%) had delayed auditory nerve function, low behavioral function, and slightly lower cognitive-language-motor function. They showed the most increasing trajectory. Profile 4 children (n = 29/35%) had very low cognitive-language-motor function, normal behavioral and auditory nerve function, but showed wide variation in their trajectory. Our preliminary study showed that a multidisciplinary profile-oriented approach may be important in children born VPT to improve counseling and provide targeted treatment for at risk children. High performers at age 2 may not be expected to maintain their favorable development. Behavioral problems might negatively impact language development. Delayed auditory nerve function might represent a slow start and catch-up development.

Functional Magnetic Resonance Imaging during Visual Perception Tasks in Adolescents Born Prematurely

OBJECTIVES

Impairments in visual perception are among the most common developmental difficulties related to being born prematurely, and they are often accompanied by problems in other developmental domains. Neural activation in participants born prematurely and full-term during tasks that assess several areas of visual perception has not been studied. To better understand the neural substrates of the visual perceptual impairments, we compared behavioral performance and brain activations during visual perception tasks in adolescents born very preterm (birth weight ≤1500 g or gestational age <32 weeks) and full-term.

METHODS

Tasks assessing visual closure, discrimination of a deviating figure, and discrimination of figure and ground from the Motor-Free Visual Perception Test, Third Edition were performed by participants born very preterm (n = 37) and full-term (n = 34) at 12 years of age during functional magnetic resonance imaging.

RESULTS

Behavioral performance in the visual perception tasks did not differ between the groups. However, during the visual closure task, brain activation was significantly stronger in the group born very preterm in a number of areas including the frontal, anterior cingulate, temporal, and posterior medial parietal/cingulate cortices, as well as in parts of the cerebellum, thalamus, and caudate nucleus.

CONCLUSIONS

Differing activations during the visual closure task potentially reflect a compensatory neural process related to premature birth or lesser neural efficiency or may be a result of the use of compensatory behavioral strategies in the study group born very preterm.

Children born before 32 weeks of gestation displayed impaired reading fluency, comprehension and spelling skills at 9 years of age

AIM

Our aim was to study whether prematurity, associated with prenatal and neonatal risk factors, affects specific literacy skills among school children born at a very low gestational age (VLGA) of <32 weeks.

METHODS

The study group comprised 76 prospectively followed VLGA children born between November 1998 and November 2002 at Oulu University Hospital, Finland, and 51 term controls. The median gestational age of the VLGA children was 29.0 (24.1-31.9) weeks. All children were examined at a median age of 8.9 (8.0-9.9) years in Oulu between November 2007 and November 2011. Reading fluency, comprehension and spelling skills were evaluated using standardised tests for Finnish-speaking children.

RESULTS

Very low gestational age children had significantly poorer test results in reading comprehension (median 6.9 vs 8.3, P = .014) and spelling (median 35.7 vs 38.0, P = .013) than term children. Furthermore, VLGA children more often performed below the 10th percentile normal values in spelling (P = .012) compared with term controls. Foetal growth restriction was associated with lower scoring in reading fluency (P = .023) and spelling (P = .004) among VLGA children.

CONCLUSION

Very low gestational age school children performed poorer in reading comprehension and spelling than term children. In addition, poor foetal growth in VLGA children was associated with literacy problems.

Language functions deserve more attention in follow-up of children born very preterm

BACKGROUND

Language is a complex neurodevelopmental phenomenon. Approximately 45% of children born very preterm (VP) show mild-to-severe language problems throughout childhood. Nevertheless, in most hospitals in Europe language functions are not routinely assessed at follow-up.

OBJECTIVE

To give clear indications for extensive language assessment in school-aged children born VP, based on routinely assessed intelligence and behavioral problems.

METHOD

Language functions of 63 10-year-old children born VP (<32 weeks' gestation) without major handicaps were compared to their intellectual and executive functions and behavioral problems. Using multiple linear regression analyses, the predictive value of perinatal factors and the association with neurodevelopmental factors of low language were measured.

RESULTS

The mean language score was significantly lower than the verbal intelligent quotient (VIQ; mean difference = 6.4, p < .001, d=.48) and the mean vocabulary knowledge (mean difference = 9.3, p < .001, d=.70). Besides, VIQ (β = .649, p = .001) and performance IQ (PIQ; β = .260, p = .035) were significantly associated with language scores. Significant predictors of language scores were number of days of assisted ventilation (β = -.592, p = .015) and mother's vocabulary knowledge (β =.473, p = .014), rather than mother's educational level (β =.139, p = .956).

CONCLUSIONS

Children born VP had language problems that were not expected from their significantly higher VIQ and vocabulary knowledge. Clinicians assessing these children should be aware of possible language problems, which cannot be detected with a simple vocabulary task. Our findings provide evidence of the need for adequate language assessments by a speech-language pathologist in children born VP, especially in those with VIQ scores in the low average range.

Language in Preterm Born Children: Atypical Development and Effects of Early Interventions on Neuroplasticity

Predicting language performances after preterm birth is challenging. It is described in the literature that early exposure to the extrauterine environment can be either detrimental or advantageous for neurodevelopment. However, the emphasis mostly lies on the fact that preterm birth may have an unfavorable effect on numerous aspects of development such as cognition, language, and behavior. Various studies reported atypical language development in preterm born children in the preschool years but also in school-aged children and adolescents. This review gives an overview of the course of language development and examines how prematurity can lead to atypical linguistic performances. In this paper, we mainly focus on environmental and neurophysiological factors influencing preterm infant neuroplasticity with potential short- and long-term effects on language development. Further research, however, should focus on examining the possible benefits that early exposure might entail.

White matter microstructure is associated with language in children born very preterm

Very preterm birth is associated with altered white matter microstructure and language difficulties, which may compromise communication, social function and academic achievement, but the relationship between these two factors is unclear. The aim of this study was to explore associations between white matter microstructure and language domains of semantics, grammar and phonological awareness at 7-years of age on a whole-brain level and within the arcuate fasciculus, an important language pathway, in very preterm and term-born children. Language was assessed in 145 very preterm-born (<30 weeks' gestation and/or <1250 g birth weight) and 33 term-born children aged 7 years. Fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), mean diffusivity (MD), axon orientation dispersion and axon density were estimated from diffusion magnetic resonance images also obtained at 7 years. The correlation between diffusion values and language was assessed using Tract-Based Spatial Statistics (TBSS). The arcuate fasciculus was delineated using constrained spherical deconvolution tractography and diffusion parameters from this tract were related to language measures using linear regression. While there was evidence for widespread associations between white matter microstructure and language, there was little evidence of differences in these associations between very preterm and term-born groups. TBSS analyses revealed that higher FA and lower AD, RD, and MD in major fibre tracts, including those subserving language, were associated with better semantic, grammar and phonological awareness performance. Higher axon density in widespread fibre tracts was also associated with better semantic performance. The tractography analyses of the arcuate fasciculus showed some evidence for associations between white matter microstructure and language outcomes. White matter microstructural organisation in widespread fibre tracts, including language-relevant pathways, was associated with language performance in whole-brain and tract-based analyses. The associations were similar for very preterm and term-born groups, despite very preterm children performing more poorly across language domains.

Relationship between mother-infant mutual dyadic responsiveness and premature infant development as measured by the Bayley III at 6 weeks corrected age

BACKGROUND

The quality of mother-preterm infant interaction has been identified as a key factor in influencing the infant's later development and language acquisition. The relationship between mother-infant responsiveness and later development may be evident early in infancy, a time period which has been understudied.

AIM

Describe the relationship between mother-infant mutual dyadic responsiveness and premature infant development.

DESIGN

This study employed a secondary analysis of data from the 6-week corrected age (CA) follow-up visit of the Hospital-Home Transition: Optimizing Prematures' Environment (H-HOPE) study, a randomized clinical trial testing the efficacy of a mother- and infant- focused intervention for improving outcomes among premature infants.

SUBJECTS

Premature infants born between 29 and 34 weeks gestational age and their mothers who had social-environmental risks.

OUTCOME MEASURES

At 6-weeks corrected age, a play session was coded for the quality of mutual responsiveness (Dyadic Mutuality Code). Development was assessed via the Bayley Scales of Infant and Toddler Development, 3rd edition.

RESULTS

Of 137 mother-infant dyads, high, medium and low mutual responsiveness was observed for 35.8%, 34.3% and 29.9%, respectively. Overall motor, language and cognitive scores were 115.8 (SD = 8.2), 108.0 (7.7) and 109.3 (7.9). Multivariable linear models showed infants in dyads with high versus low mutual responsiveness had higher scores on the motor (β = 3.07, p = 0.06) and language (β = 4.47, p = 0.006) scales.

CONCLUSION

High mutual responsiveness in mother-premature infant dyads is associated with significantly better language development and marginally better motor development.

Triplets, birthweight, and handedness

The mechanisms behind handedness formation in humans are still poorly understood. Very low birthweight is associated with higher odds of left-handedness, but whether this is due to low birthweight itself or premature birth is unknown. Handedness has also been linked to development, but the role of birthweight behind this association is unclear. Knowing that birthweight is lower in multiple births, triplets being about 1.5 kg lighter in comparison with singletons, and that multiples have a higher prevalence of left-handedness than singletons, we studied the association between birthweight and handedness in two large samples consisting exclusively of triplets from Japan (n = 1,305) and the Netherlands (n = 947). In both samples, left-handers had significantly lower birthweight (Japanese mean = 1,599 g [95% confidence interval (CI): 1,526-1,672 g]; Dutch mean = 1,794 g [95% CI: 1,709-1,879 g]) compared with right-handers (Japanese mean = 1,727 g [95% CI: 1,699-1,755 g]; Dutch mean = 1,903 g [95% CI: 1,867-1,938 g]). Within-family and between-family analyses both suggested that left-handedness is associated with lower birthweight, also when fully controlling for gestational age. Left-handers also had significantly delayed motor development and smaller infant head circumference compared with right-handers, but these associations diluted and became nonsignificant when controlling for birthweight. Our study in triplets provides evidence for the link between low birthweight and left-handedness. Our results also suggest that developmental differences between left- and right-handers are due to a shared etiology associated with low birthweight.

Cortical morphometry and cognition in very preterm and term-born children at early school age

Very preterm birth influences brain development and may result in alterations of cortical morphometry. These structural alterations may interact with cognitive development. The aim of the present study was to investigate the structure-function relationship in school-aged very preterm and term-born control children. A comprehensive neuropsychological test battery was administered to 41 very preterm (<32 weeks of gestation) and 30 term-born control children aged seven to twelve years. The automated method FreeSurfer was used to obtain cortical thickness and cortical surface area measures from T1-weighted MRI images. Regional cortical thickness differed between groups but differences disappeared when controlling for age. Global cortical thickness differed between groups in the right hemisphere (very preterm children>controls). No group differences occurred for cortical surface area. The relationship between cortical morphometry and cognition differed between very preterm and control children. In very preterm children, some cognitive domains correlated positively and others negatively with regional cortical thickness and cortical surface area. Our findings contribute to the understanding of the structure-function relationship in very preterm children and their term-born peers. They add to the notion that this relationship varies depending on the brain region and the cognitive function in question and suggest developmental differences between very preterm and term-born children.

Limited microstructural and connectivity deficits despite subcortical volume reductions in school-aged children born preterm with very low birth weight

Preterm birth and very low birth weight (VLBW, ≤1500 g) are worldwide problems that burden survivors with lifelong cognitive, psychological, and physical challenges. In this multimodal structural magnetic resonance imaging (MRI) and diffusion MRI (dMRI) study, we investigated differences in subcortical brain volumes and white matter tract properties in children born preterm with VLBW compared to term-born controls (mean age=8 years). Subcortical brain structure volumes and cortical thickness estimates were obtained, and fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) were generated for 18 white matter tracts. We also assessed structural relationships between white matter tracts and cortical thickness of the tract endpoints. Compared to controls, the VLBW group had reduced volumes of thalamus, globus pallidus, corpus callosum, cerebral white matter, ventral diencephalon, and brain stem, while the ventricular system was larger in VLBW subjects, after controlling for age, sex, IQ, and estimated total intracranial volume. For the dMRI parameters, group differences were not significant at the whole-tract level, though pointwise analysis found shorter segments affected in forceps minor and left superior longitudinal fasciculus - temporal bundle. IQ did not correlate with subcortical volumes or dMRI measures in the VLBW group. While the deviations in subcortical volumes were substantial, there were few differences in dMRI measures between the two groups, which may reflect the influence of advances in perinatal care on white matter development.