Presentation

Juhi Kidwai¹, E. Susan Duncan², Adam Buchwald¹; ¹New York University, ²Louisiana State University

Past research suggests that functional brain networks underlying speech can be bilateral at rest and left-lateralized during speech production[1]. This seeming contradiction may reflect differences between the dorsal and ventral streams for speech, which are putatively left-lateralized or bilaterally distributed, respectively[2]. In this Sandbox series abstract, we explore the lateralization of dorsal speech production functional networks at rest in healthy older adults. For this purpose, we selected an area in ventral precentral gyrus associated with tongue and larynx in the left hemisphere and its homolog in the right hemisphere. We chose this region because of its unambiguous involvement in speech production, and defined the region based on the Brainnetome Atlas that specifies a tongue-larynx (T-L) region in the ventral precentral gyrus based upon functional and structural connectivity data[3]. Resting-state functional magnetic resonance imaging (rs-fMRI) data of healthy older adults (n = 46, M = 58.89 ± 8.29 y) from the publicly available OASIS-3 database were used to analyze the connectivity in the T-L regions[4]. After motion correction, anatomical images were aligned with rs-fMRI data to facilitate spatial normalization, followed by spatial smoothing, regression of nuisance variables, and bandpass filtering. Participants with a minimum of 9 minutes of usable data were retained[5, 6]. We conducted whole brain correlation analyses using the first eigenvariate time series of three seed regions: left T-L region, right T-L region, and a region defined as the bilateral combination of those two. We computed the eigenvariate to find the central tendency in activity of each seed region and extracted this time series for each seed for each subject. Linear correlation coefficients were then computed for the extracted time series for each seed with the time series from every other voxel in the brain. Voxel-wise correlation coefficients were converted into Fisher’s z-scores to permit comparison across participants. We first compared the correlations of the eigenvariate from left T-L with right T-L using a paired t-test with AFNI’s 3dClustSim to control for false positives (corrected p <0.01). We primarily observed differences in the areas adjacent to left T-L and right T-L, in which each region was more strongly connected to the ipsilateral adjacent voxels. In addition, we observed a stronger correlation between right T-L and the rostroventral area of the right inferior parietal lobule (near the temporal-parietal junction) with no analogous finding on the left. A second analysis compared the functional connections of the bilaterally defined region (left + right T-L) with the whole brain. We observed that this bilaterally defined region was correlated to perisylvian regions in each hemisphere. Additionally, we compared the eigenvariate of the bilaterally defined region with each of the unilateral regions; there were no areas associated with the dual route speech and language processing system that were more associated with the lateralized regions than the bilateral regions. This suggests that even at the level of ventral precentral gyrus associated with the tongue-larynx, the functional connectivity at rest between this area and the rest of the language system is best defined bilaterally.

Topic Areas: Speech Motor Control, Language Production