Subcortical correlates of developmental language disorder: more than the neostriatum.

Developmental language disorder (DLD) is a common neurodevelopmental disorder that affects receptive and expressive language skills. In contrast to the wealth of evidence on acquired language disorders, we understand relatively little about the neural underpinnings of DLD. A recent meta-analysis across different types of structural brain analyses in DLD highlighted consistent anatomical differences in the anterior striatum, with other subcortical structures relatively spared. These findings are consistent with predictions from the procedural circuit deficit hypothesis (PCDH), namely that the anterior neostriatum differs in structure and function in DLD, whereas medial temporal lobe structures are unaffected and may act in a compensatory manner. Here, in a case-control study with a larger sample size than previous studies, we evaluated volume and microstructure of subcortical grey matter structures using T1-weighted images and diffusion imaging. Our predictions were partly in accord with those of the PCDH and the findings of the meta-analysis. Neuroimaging and behavioural measures were acquired in 156 children and adolescents (54 DLD; 74 typically developing (TD); 28 with a history of language difficulties) aged 10:0-15:11 years. As predicted by the PCDH, there were significant differences in the DLD group in volume and microstructure of the neostriatum (caudate nucleus, putamen). However, in contrast to our prediction, there were also significantly smaller structures in the DLD group across other subcortical structures evaluated: globus pallidus, thalamus and hippocampus. The hippocampal difference is of particular interest as it is hypothesized in the PCDH to be spared in DLD. Microstructural measures (diffusion tensor imaging and neurite orientation dispersion and density imaging) revealed differences in the caudate nucleus, thalamus and hippocampus. Multivariate machine learning analyses highlighted the relationship between the hippocampus and language skills but only in the TD cohort. We conclude that the subcortical correlates of DLD are in fact not limited to the neostriatum and represent important areas of further inquiry.