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Sentence comprehension requires the integration of linguistic units presented in a temporal sequence based on a non-linear underlying syntactic structure. While it is uncontroversial that storage is mandatory for this process, there are opposing views regarding the relevance of general short-term-/working-memory capacities (STM/WM) versus language specific resources. Here we report results from 43 participants with an acquired brain lesion in the extended left hemispheric language network and resulting language deficits, who performed a sentence-to-picture matching task and an experimental task assessing phonological short-term memory. The sentence task systematically varied syntactic complexity (embedding depth and argument order) while lengths, number of propositions and plausibility were kept constant. Clinical data including digit-/ block-spans and lesion size and site were additionally used in the analyses. Correlational analyses confirm that performance on STM/WM-tasks (experimental task and digit-span) are the only two relevant predictors for correct sentence-picture-matching, while reaction times only depended on age and lesion size. Notably increasing syntactic complexity reduced the correlational strength speaking for the additional recruitment of language specific resources independent of more general verbal STM/WM capacities, when resolving complex syntactic structure. The complementary lesion-behaviour analysis yielded different lesion volumes correlating with either the sentence-task or the STM-task. Factoring out STM measures lesions in the anterior temporal lobe correlated with a larger decrease in accuracy with increasing syntactic complexity. We conclude that overall sentence comprehension depends on STM/WM capacity, while increases in syntactic complexity tax another independent cognitive resource.

The breakdown of rapid and accurate retrieval of words is a hallmark of aphasic speech and a prime target of therapeutic intervention. Complementary, psycho- and neurolinguistic research have developed a spectrum of models, how and by which neuronal network uncompromised speakers can rely on remarkable lexical retrieval capacities. Motivated by both lines of research we invited 32 participants with a chronic left hemispheric brain lesion to name pictures in the presence of distractor words. This picture-word-interference (PWI) paradigm is widely used in psycho- and neurolinguistic research.We find that also after brain lesion categorically related words (CAT → [dog]picture) impede naming, while associatively related words (BONE → [dog]picture) ease access, when compared to unrelated distractor words. The effects largely affecting latencies in neurotypical populations, are reproduced for error rate in our participants with lesions in the language network. Unsurprisingly, overall naming abilities varied greatly across patients. Notably, however, the two effects (categorical interference / associative facilitation) differ between participants. Correlating performance with lesion patterns we find support for the notion of a divergence of brain areas affording different aspects of the task: (i) lesions in the left middle temporal gyurs (MTG) deteriorate overall naming, confirming previous work; more notably, (ii) lesions comprising the inferior frontal hub (inferior frontal gyrus, IFG) of the language-network increase the interference effect for the categorical condition; on the contrary, (iii) lesions to the mid-to-posterior temporal hub (posterior middle and superior temporal gyri, pMTG/ pSTG) increase the facilitatory effect for the associative condition on error rates.The findings can be accommodated in a neuro-linguistic framework, which localizes lexical activation but also lexical interference in posterior parts of the language network (pMTG/pITG); conversely, selection between co-activated categorically related entries is afforded by frontal language areas (IFG). While purely experimental in nature our study highlights that lesion site differentially influences specific aspects of word retrieval. Since confrontational naming is a cornerstone of aphasia rehabilitation, this may be of note when designing and evaluating novel therapeutic regimes.