Poster D57, Wednesday, August 21, 2019, 5:15 – 7:00 pm, Restaurant Hall
The frontal aslant white matter tract (FAT) and semantic selection in word production
Joanna Sierpowska1,2, Nikki Janssen1,2, Roy P.C. Kessels1,2, Ardi Roelofs1, Vitória Piai1,2;1Radboud University, Donders Institute for Brain, Cognition and Behaviour, 2Radboud University Medical Center, Donders Institute for Brain Cognition and Behaviour, Department of Medical Psychology, Nijmegen, The Netherlands
[Introduction] The frontal aslant tract (FAT) is a white matter structure joining the anterior supplementary and pre-supplementary motor area (SMA and pre-SMA) with the inferior and middle frontal gyri. The FAT shows leftward asymmetry (Catani et al., 2012), suggesting a role in language processing. Although previous studies showed the contribution of the FAT in speech motor control (Kinoshita at al., 2015; Kemerdere et al., 2016), the exact character of the FAT as a functional connection remains poorly understood. Previously, we reported that direct electrical stimulation applied at the level of the left FAT during brain surgery provoked overregularization errors in verb generation (Sierpowska et al., 2015). This case study motivated us to examine the relationship between the microstructural properties of the FAT and performance in a demanding verb generation task in healthy individuals and to test whether it follows a left-lateralization pattern. [Methods] 50 healthy participants (mean age=43.7±21.6) were scanned with high-resolution diffusion-weighted imaging (DWI) and underwent behavioral testing using a verb generation task (dataset shared by Janssen et al., in prep). Stimuli consisted of 100 high-frequency concrete Dutch nouns (e.g. “hond” [dog]). Verbs could not be formed by the morphological derivation of the noun. Based on the responses given by the participants, we sorted the items into high and low selection demands (Thompson-Schill et al., 1998). The FAT connection was obtained using two regions of interest (ROI) and one exclusion mask. The ROIs were defined within the MNI space according to the following neuroanatomical landmarks: (1) the SMA and pre-SMA, conjoined and (2) the pars triangularis and opercularis of the inferior frontal gyrus (IFG, conjoined). The exclusion mask was defined around the midline on a sagittal section. Subsequently, the masks were transferred to each individual’s diffusion space and their corresponding white matter circuitry was calculated using a probabilistic approach (FSL probtrackx). All individual results were then binarized and used as masks to derive fractional anisotropy (FA) values, further used for comparison with behavioral data (Spearman correlations). [Results] FA values of the left FAT correlated with accuracy in verb generation, but only for the high selection condition (r(49)=.278; P=.025). Additionally, strong correlations were found between the right FAT FA values and accuracy for both high (r(49)=.611; P<.001) and low selection conditions (r(49)=.459; P<.001). [Conclusion] This study confirms that the previously found relationship between the left FAT and performance on verb generation is also apparent in healthy individuals. Additionally, the fact that this relationship only holds for items with high selection demands suggests that semantic control mechanisms underlie the left FAT role in language. Finally, the newly observed relationship between verb generation and the same tract in the right hemisphere, typically non-dominant for language, opens a new direction for further studies. In the neurosurgical context, these results may aid in further establishing language monitoring protocols for protecting white matter connectivity in surgeries for removal of tumors subjacent to both left and right (pre)SMA.
Themes: Language Production, Meaning: Lexical Semantics
Method: White Matter Imaging (dMRI, DSI, DKI)