Poster E1, Thursday, August 22, 2019, 3:45 – 5:30 pm, Restaurant Hall
The role of the left frontal aslant tract in lexical selection: data from picture-word interference and sentence completion tasks
Andrey Zyryanov1, Svetlana Malyutina1,2, Olga Dragoy1,2;1National Research University Higher School of Economics, Moscow, 2Federal Center for Cerebrovascular Pathology and Stroke, Moscow
Interference resolution (IR) between the target lemma and co-activated semantically related lemmas during lexical selection involves the left inferior frontal gyrus (IFG), as suggested by fMRI studies of picture-word interference (PWI) contrasting naming with a semantically related distractor (high IR demands) against naming with an unrelated distractor or without a distractor (low IR demands). However, evidence from lesion studies is somewhat mixed: although damage to the IFG selectively impairs sentence completion (SC) task performance in low-constraint sentences, i.e. under high lexical selection demands (Robinson et al., 1998), it does not result in selectively longer latencies of naming with semantically related distractors compared to unrelated distractors in the PWI task (Piai & Knight, 2018), which questions its critical contribution to the IR during lexical selection. Based on studies showing the role of pre-supplementary motor area (pre-SMA) in lexical selection (Alario et al., 2006; Piai et al., 2014), we hypothesized that the connectivity between the IFG and pre-SMA via the frontal aslant tract (FAT) underlies lexical selection. To test our hypothesis, we investigated the effect of FAT disconnection on SC and PWI performance. Twenty patients with a single left-hemisphere stroke involving the frontal lobe (age: mean 57.4 years, range 42–70; months post-onset: mean 24.6, range 1.9–88) performed the PWI task with semantic, unrelated and congruent distractors and the SC task with high versus low semantic constraint. Based on diffusion MRI (1.5T scanner, 64 diffusion directions, b-value 1000 s/mm2), we performed tensor-based whole-brain tractography, manually reconstructed the left FAT and extracted its volume in individual participants, corrected for whole-brain volume. T1-, T2- and FLAIR-weighted images were used to delineate lesions and calculate the total lesion volume and lesion load in pars triangularis and pars opercularis of the IFG. PWI naming latencies, PWI accuracy and SC accuracy were analysed in linear mixed-effects models including condition, anatomical predictor (FAT volume or IFG load), their interaction and total lesion volume as fixed effects, and participant and item as random effects. As expected, in the PWI task, semantically related condition was associated with slower (p<0.001) and less accurate (p<0.001) naming compared to congruent condition, with no difference between semantically related and unrelated condition. We found significantly lower PWI accuracy (p=0.007) and a trend for slower PWI naming latencies (p=0.072) in participants with lower FAT volume but no interaction between FAT volume and condition, suggesting that FAT mediates PWI performance regardless of IR demands. No effects of IFG damage on PWI performance were observed. By contrast, lower SC accuracy was predicted by greater IFG damage (p=0.002), low semantic constraint (p<0.001) and their interaction (p=0.002), but not lower FAT volume (p=0.293), consistent with the established role of IFG in lexical selection. A post-hoc error type analysis of PWI data revealed that lower FAT volume was associated with increased likelihood of suppression (p=0.003), but not semantic (p=0.091), errors. Our findings do not support the critical contribution of FAT to IR during lexical selection, but rather point to its role in PWI-specific distractor processing.
Themes: Control, Selection, and Executive Processes, Meaning: Lexical Semantics
Method: White Matter Imaging (dMRI, DSI, DKI)