While current dual-steam neurocognitive models of language function have coalesced around the view that distinct neuroanatomical networks subserve semantic and phonological processing, respectively, the specific white matter components of these networks remain a matter of debate. To inform this debate, we investigated relationships between structural white matter connectivity and word production in a cross-sectional study of 42 participants with aphasia due to unilateral left hemisphere stroke. Specifically, we reconstructed a local connectome matrix for each participant from diffusion spectrum imaging data and regressed these matrices on indices of semantic and phonological ability derived from their responses to a picture-naming test and a computational model of word production. These connectometry analyses indicated that both dorsally located (arcuate fasciculus) and ventrally located (inferior frontal-occipital, uncinate, and middle longitudinal fasciculi) tracts were associated with semantic ability, while associations with phonological ability were more dorsally situated, including the arcuate and middle longitudinal fasciculi. Associations with limbic pathways including the posterior cingulum bundle and the fornix were also found. All analyses controlled for total lesion volume and all results showing positive associations obtained false discovery rates < 0.05. These results challenge dual-stream accounts that deny a role for the arcuate fasciculus in semantic processing, and for ventral-stream pathways in language production. They also illuminate limbic contributions to both semantic and phonological processing for word production.

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The information theoretic principle of rational adaptation predicts that individuals with aphasia adapt to their language impairments by relying more heavily on comparatively unimpaired non-linguistic knowledge to communicate. This prediction was examined by assessing the extent to which adults with chronic aphasia due to left-hemisphere stroke rely more on conceptual rather than lexical information during verb retrieval, as compared to age-matched neurotypical controls. A primed verb naming task examined the degree of facilitation each participant group received from either conceptual event-related or lexical collocate cues, compared to unrelated baseline cues. The results provide evidence that adults with aphasia received amplified facilitation from conceptual cues compared to controls, whereas healthy controls received greater facilitation from lexical cues. This indicates that adaptation to alternative and relatively unimpaired information may facilitate successful word retrieval in aphasia. Implications for models of rational adaptation and clinical neurorehabilitation are discussed.

Background: Current neurocognitive models of language function have been primarily built from evidence regarding object naming, and their hypothesized white matter circuit mechanisms tend to be coarse-grained. Methods: In this cross-sectional, observational study, we used novel correlational tractography to assess the white matter circuit mechanism behind verb retrieval, measured via action picture-naming performance in adults with chronic aphasia. Results: The analysis identified tracts implicated in current neurocognitive dual-stream models of language function, including the left inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, and arcuate fasciculus. However, the majority of tracts associated with verb retrieval were not ones included in dual-stream models of language function. Instead, they were projection pathways that connect frontal and parietal cortices to subcortical regions associated with motor functions, including the left corticothalamic pathway, frontopontine tract, parietopontine tract, corticostriatal pathway, and corticospinal tract. Conclusions: These results highlight that cortico-subcortical projection pathways implicated in motor functions may be importantly related to language function. This finding is consistent with grounded accounts of cognition and may furthermore inform neurocognitive models.

Warren and Dresang comment on the contributions from a psycholinguistic perspective, highlighting close relations between the respective research on events and proposing that, for example, verbs may indeed directly pre‐activate templates of the typically involved event participants.

These results challenge assumptions regarding intact implicit processing in adults with traumatic brain injury, and reveal mechanisms by which communication could fail in everyday social interactions.

Verb-retrieval impairments are pervasive deficits that can negatively impact communicative function for individuals living with aphasia. Unfortunately, the neurocognitive basis of these deficits remains poorly understood. One open question is the degree to which verb-retrieval impairments might be rooted in lexical- versus conceptual-processing deficits. These deficits can be co-present and correlated in people with aphasia, but they have also been found to be dissociated in patients with a variety of acquired brain injuries. This study examined the degree to which conceptual versus lexical action-processing abilities are impaired and may contribute to verb-retrieval impairments in adults with chronic aphasia due to left-hemisphere stroke. The results indicate that conceptual action processing can be impaired in aphasia and may contribute to verb-retrieval impairments. Furthermore, relatively unimpaired conceptual processing can ameliorate the influence of lexical impairments on verb-retrieval impairments. These findings are consistent with models in which conceptual representations play a key role in language processing and may be leveraged to improve verb retrieval in adults with chronic aphasia.