As the phylogenetic evolutionary development of the
As the phylogenetic evolutionary development of the glycoprotein iib iiia inhibitors has been associated with the evolvement of language, it is suggested that the ontogenetic maturation, especially of the prefrontal cortex, can be related to language acquisition (e.g., Thompson-Schill et al., 2009). Prior structural imaging work found initial evidence for the link between structural gray matter changes and the development of language performance in children: Infants’ gray matter maturation of the right cerebellum and the right hippocampus was found to correlate with later language competence (Deniz Can et al., 2013). The receptive and productive phonological skills of children aged between 5 and 11 years correlate with measurements of gray matter probability (GMP) in the left inferior frontal gyrus (IFG; Lu et al., 2007). In teenagers aged between 12 and 17 years, gray matter of the left supramarginal gyrus and left posterior temporal regions correlate with vocabulary knowledge (Richardson et al., 2010). However, no study to date closely examined gray matter maturation in relation to the processing of syntactically complex sentences. Frontal and parietal areas have been shown to be involved in complex sentence processing (for a review, see Friederici, 2011). With regard to brain structure, the frontal and parietal lobe demonstrate an increase of gray matter during childhood (Giedd et al., 1999; Lenroot et al., 2007; Matsuzawa et al., 2001; Shaw et al., 2008) and an onset of gray matter loss around 9.6 years (frontal) and 10.7 years (temporal) of age (Tanaka et al., 2012).
Sentence comprehension crucially depends on determining the thematic relationship of noun phrases, that is, on identifying who is doing what to whom. While in English, word order provides a reliable cue for assigning thematic roles to noun phrases (i.e., agent, theme and goal), in German, the assignment additionally depends on processing morphological information such as case-marking. Behaviorally, it has been reported that German-speaking children cannot reliably process this kind of morphological information up to the age of 7 years (Dittmar et al., 2008; Schipke et al., 2012). In addition, several studies found that before 7 years of age, children do not demonstrate reliable subvocal rehearsal that increase verbal working memory capacity and, consequently, facilitate complex sentence processing (e.g., Gathercole et al., 2004; Gathercole and Hitch, 1993).
To elucidate on the missing link between brain structural properties of cortical regions relevant for complex sentence processing and the establishment of grammatical proficiency, we investigated the interrelation between GMP in language-relevant brain areas and specific cognitive abilities underlying complex sentence comprehension. To do this, whole-brain magnetic resonance images from 59 children aged between 5 and 8 years were assessed and analyzed using voxel-based morphometry (VBM). We determined grammatical proficiency by scores attained from grammar-specific subtests of the German version of the Test for the Reception of Grammar (TROG-D; Fox, 2006): Here, only sentences that required specific morphological and syntactic knowledge were included in the analysis. To segregate different contributions of grammatical knowledge and verbal working memory capacity to the comprehension of complex sentences, a principal component analysis was run on the participants’ behavioral data. To investigate a relation between these two factors and GMP on whole-brain level, a multiple regression analysis was performed. Finally, since the maturation of the prefrontal cortex has been associated with the development of linguistic conventions (Thompson-Schill et al., 2009) and the processing of syntactically complex sentences typically engages the left IFG (for a review, see Friederici, 2011), additional correlational analyses were restricted to this specific region.