Neuroanatomical Prerequisites for Language Functions in the Maturing Brain

Abstract

The 2 major language-relevant cortical regions in the human brain, Broca's area and Wernicke's area, are connected via the fibers of the arcuate fasciculus/superior longitudinal fasciculus (AF/SLF). Here, we compared this pathway in adults and children and its relation to language processing during development. Comparison of fiber properties demonstrated lower anisotropy in children's AF/SLF, arguing for an immature status of this particular pathway with conceivably a lower degree of myelination. Combined diffusion tensor imaging (DTI) data and functional magnetic resonance imaging (fMRI) data indicated that in adults the termination of the AF/SLF fiber projection is compatible with functional activation in Broca's area, that is pars opercularis. In children, activation in Broca's area extended from the pars opercularis into the pars triangularis revealing an alternative connection to the temporal lobe (Wernicke's area) via the ventrally projecting extreme capsule fiber system. fMRI and DTI data converge to indicate that adults make use of a more confined language network than children based on ongoing maturation of the structural network. Our data suggest relations between language development and brain maturation and, moreover, indicate the brain's plasticity to adjust its function to available structural prerequisites.

Microstructures of Learning: Novel methods and approaches for assessing structural and functional changes underlying knowledge acquisition in the brain

“…The ventral network can partially compensate for the dorsal interference and therefore seems to play an important role even when no semantic information is available. This result is consistent with developmental data (Brauer et al, 2011) and reports of recovery after lesions in the dorsal pathway (Yeatman and Feldman, 2013).…”

“…Direct connections between these language-related areas in the left frontal and temporal cortices are sustained dorsally through the arcuate fasciculus and ventrally by paths running through the extreme capsule (Saur et al, 2008;Brauer et al, 2011Brauer et al, , 2013. The dorsal connection is also assured indirectly through the parietal lobe (Geschwind territory) with shorter segments (Catani et al, 2005): an anterior segment connecting Broca's and Geschwind territories, and a posterior segment connection between Geschwind and Wernicke's territories ( Figure 1).…”

Cortical activity during speech and non-speech oromotor tasks: A magnetoencephalography (MEG) study

“…While it is agreed that both ventral and dorsal pathways connect language centres in the brain, the exact contributions of each pathway are a matter of debate [11], but it is thought that the dorsal pathway is involved in more complex syntactic functions while the ventral path is involved in comprehension (see [3]). In the current study, the spatiotemporal sequence following stimulus onset involves the ventral pathway while the spatiotemporal sequence preceding maximal jaw displacement involves the dorsal pathway.…”

Components of the Language-Ready Brain

“…Direct connections between the language-related areas in the left frontal and temporal cortices are sustained dorsally through the arcuate fasciculus (AF) and ventrally by paths running through the extreme capsule (Saur et al, 2008;Brauer et al, 2011Brauer et al, , 2013. The dorsal connection is also assured indirectly through the parietal lobe with shorter segments (Catani et al, 2005): an anterior segment connecting the premotor and inferior frontal regions with the IPL and a posterior segment connecting inferior parietal and temporal cortices (Figure 2, right).…”

“…In contrast, the dorsal pathway follows different developmental courses, with two subparts maturing at different rates. Whereas the dorsal connections reaching the premotor cortex are functional at birth, the terminations of the dorsal pathway reaching the posterior portion of Broca's area (BA 44) are still underdeveloped (Perani et al, 2011) and are not fully myelinated at the age of seven (Brauer et al, 2011(Brauer et al, , 2013. Adult studies on the learning of new languages indicate that whereas the audio-motor subpart is related to word learning (López-Barroso et al, 2013), the processing of non-adjacent elements relies on the latter subpart running from frontal BA 44 .…”