Interactions between White Matter Asymmetry and Language during Neurodevelopment

Abstract

The human brain is asymmetric in gross structure as well as functional organization. However, the developmental basis and trajectory of this asymmetry is unclear, and its relationship(s) to functional and cognitive development, especially language, remain to be fully elucidated. During infancy and early childhood, in concert with cortical gray matter growth, underlying axonal bundles become progressively myelinated. This myelination is critical for efficient and coherent interneuronal communication and, as revealed in animal studies, the degree of myelination changes in response to environment and neuronal activity. Using a novel quantitative magnetic resonance imaging method to investigate myelin content in vivo in human infants and young children, we investigated gross asymmetry of myelin in a large cohort of 108 typically developing children between 1 and 6 years of age, hypothesizing that asymmetry would predict language abilities in this cohort. While asymmetry of myelin content was evident in multiple cortical and subcortical regions, language ability was predicted only by leftward asymmetry of caudate and frontal cortex myelin content and rightward asymmetry in the extreme capsule. Importantly, the influence of this asymmetry was found to change with age, suggesting an age-specific influence of structure and myelin on language function. The relationship between language ability and asymmetry of myelin stabilized at ϳ4 years, indicating anatomical evidence for a critical time during development before which environmental influence on cognition may be greatest.

White matter development and early cognition in babies and toddlers

“…This is the first study to demonstrate this relationship with the developing myelin volume fraction. These results reinforce our recent findings demonstrating age-specific associations between white matter asymmetry and cognition in an overlapping age group [O'Muircheartaigh et al, 2013]. …”

“…How this development is associated with cognitive maturation, and how individual differences may predict individual cognitive and functional ability during this period remains unclear. Previous work by our group has investigated the relationship between asymmetry of VF M and cognitive abilities and indicated age-specific relationships between subcortical and mesial frontal white matter asymmetry and language abilities [O'Muircheartaigh et al, 2013]. Contrary to expectations, no relationship was seen in asymmetry of the white matter underlying classical language areas, even though leftward asymmetry was evident in the arcuate fasciculus.…”

“…This log-transformed age variable was included due to the predicted log-shaped, nonlinear VF M growth trajectory [Deoni et al, 2012b]. The testing of the cognition-age interactions were included in the model to investigate the temporal stability of any cognitive relationships over the age period studied here [O'Muircheartaigh et al, 2013]. To account for multiple comparisons, we used the false discovery rate (FDR) correction [Benjamini and Hochberg, 1995] at a desired FDR rate of q = 0.05 (where q indicates the expected proportion of erroneously rejected null hypotheses among the rejected ones) and this single rate was applied across all tests.…”

Meta-analytic investigations of structural grey matter, executive domain-related functional activations, and white matter diffusivity in obsessive compulsive disorder: An integrative review

“…Existing studies demonstrated substantial neurodevelopment changes in white matter diffusivity as the brain matures (Kochunov and Hong, 2014;O'Muircheartaigh et al, 2013). Considering that white matter fibres facilitate neural transmission between connecting regions, neurodevelopment changes in white matter diffusivity would translate to changes in grey matter volumes and function of the connecting structures.…”

Social Neuroscience and Theory of Mind

“…Brain circuits associated with language are more flexible before the age of 4, and environmental influences have their biggest impact before the age of 4. Consequently, early intervention for children should be initiated before this critical age [93]. SLPs can be in position to advocate for policy changes to promote the mental health and language development of at-risk children.…”