A general role for ventral white matter pathways in morphological processing: going beyond reading

Abstract

The ability to recognize the structural components of words, known as morphological processing, was recently associated with the bilateral ventral white matter pathways, across different writing systems. However, it remains unclear whether these associations are specific to the context of reading. To shed light on this question, in the current study we investigated whether the ventral pathways are associated with morphological processing in an oral word production task that does not involve reading. Forty-five participants completed a morphemebased fluency task in Hebrew, as well as diffusion MRI (dMRI) scans. We used probabilistic tractography to segment the major ventral and dorsal white matter pathways, and assessed the correlations between their microstructural properties and performance on the morpheme-based fluency task. We found significant correlations between morpheme-based fluency and properties of the bilateral ventral tracts, suggesting that the involvement of these tracts in morphological processing extends beyond the reading modality. In addition, significant correlations were found in the frontal aslant tract (FAT), a dorsal tract associated with oral fluency and speech production. Together, our findings emphasize that neurocognitive associations reflect both the cognitive construct under investigation as well as the task used for its assessment. Lastly, to elucidate the biological factors underlying these correlations, we incorporated the composite hindered and restricted model of diffusion (CHARMED) framework, measured in independent scans. We found that only some of our findings could be attributed to variation in a CHARMEDbased estimate of fiber density. Further, we were able to uncover additional correlations that could not be detected using traditional dMRI indices. In sum, our results show that the involvement of the ventral tracts in morphological processing extends to the production domain, and demonstrate the added value of including sensitive structural measurements in neurocognitive investigations.

Evaluating the Reliability of Human Brain White Matter Tractometry

“…Our high subject-level robustness results (Figs. 4C, 5C, 6C) dovetail with the results of a recently published study that used tractometry in a sample of 45 participants (51) and found high subject-level correlations between the mean tract values of FA and MD for two different pipelines: deterministic tractography using the diffusion tensor model (DTI) as the ODF model (essentially identical to a pipeline used in our supplementary analysis, described in "DTI Configuration") and probabilistic tractography using CSD as the ODF model. Consistent with our results on the HCP-TR dataset, slightly higher subject robustness was found for MD than for FA.…”

A review of the anatomy and function of the white matter tracts in language production and comprehension

“…It is worth mentioning that FAT is often implicated in verbal fluency tasks along with other tracts, especially IFOF, although the evidence is, as in the other cases, far from convergent. Some studies have reported a correlation with both category and letter fluency scores (Blecher et al, 2019;Costentin et al, 2019;Li et al, 2017;Sanvito et al, 2020), some only with letter/phoneme fluency (Cipolotti et al, 2016;Keser et al, 2020), some with morpheme-based fluency (Yablonski et al, 2021) and some with none of these (Tseng et al, 2019;Vallesi & Babcock, 2020). Costentin et al (2019) found a correlation between verbal fluency scores and lesions to FAT and a number of other tracts in 48 individuals with Parkinson's Disease.…”

The Contributions of the Cerebellar Peduncles and the Frontal Aslant Tract in Mediating Speech Fluency

“…Forty-five neurotypical adults (29 females; mean age 26.45 ± 3.72 years; Table 1) were recruited for this study. All the analyses reported here are completely new, but some data from this sample has been reported as part of a research project focusing on associations between well-known language pathways and word structure (Yablonski et al, 2021;. All participants were right handed as estimated by the Edinburgh handedness inventory (Oldfield, 1971; Table 1), and had no history of a diagnosed speech impairment, learning disability, or neurological condition.…”

“…We also calculated a standardized verbal fluency score based on age-appropriate Hebrew norms (Kavé & Knafo-Noam, 2015). The analysis of standardized verbal fluency scores in the current sample is reported in a previous paper (Yablonski et al, 2021). Note, however, that this previous paper did not examine the associations between verbal fluency measures and the CPs, which is the focus of the current study.…”

“…Preprocessing was implemented in the native space of each individual, following a published pipeline (Yablonski et al, 2021). This pipeline included several steps: (1)…”