This was demonstrated by strong correlations between reduced FA in the SLF/Arcuate and deficits

in syntactic comprehension and production. In contrast, we found that damage to ventral tracts—the extreme capsule fiber system or the uncinate fasciculus—does not result in syntactic deficits. When other potentially important factors were included as covariates, the integrity of the SLF/Arcuate continued to be associated with Romidepsin syntactic processing function. Specifically, we observed relationships between FA in the SLF/Arcuate and syntactic comprehension and production when we took into account PPA variant, overall severity, executive function, motor speech, and gray matter atrophy in the left IFG, the cortical region most associated with

syntactic deficits. These analyses indicate that although these factors certainly may contribute to syntactic deficits, the SLF/Arcuate makes a unique contribution to syntactic processing even when these other factors are accounted for. Furthermore, the fact that we found robust correlations with both syntactic comprehension and production measures makes it less likely that the deficits resulting from SLF/Arcuate damage reflect component processes such as executive functions or motor speech. A key role for the SLF/Arcuate in syntactic processing has been suggested previously based on indirect evidence from fiber tracking connecting regions activated in an NVP-BGJ398 very fMRI study of syntactic processing (Friederici et al., 2006). Our findings provide more direct evidence for the importance of dorsal tracts for syntactic processing, by showing that damage to these tracts results in syntactic deficits. Syntax is perhaps the most uniquely human component of language, due to its hierarchical structure, unparalleled complexity, and recursion, which gives rise to infinite generativity. Therefore, it might be expected that the neural substrate(s) for syntactic processing might have been significantly

modified over the course of human evolution. A recent comparative DTI study reported that the arcuate branch of the SLF is indeed strongly modified in humans relative to nonhuman primates; it projects much more densely to posterior temporal cortex than it does in macaques or chimpanzees, especially in the left hemisphere (Rilling et al., 2008). Recent studies have established the importance of ventral tracts including the ECFS and UF in language processing (Friederici et al., 2006, Friederici, 2009, Saur et al., 2008 and Weiller et al., 2009). Our results support the importance of these tracts in language processing, indicating that they may play a role in lexical processing at the single word level. Ventral tracts are most severely affected in patients with semantic variant PPA (Galantucci et al., 2011), who present with profound lexical deficits encompassing lexical retrieval, single word comprehension, and semantic knowledge (Hodges and Patterson, 1996).