Poster D5, Friday, August 17, 4:45 – 6:30 pm, Room 2000AB

Speech rate is associated with cerebellar white matter in persistent developmental stuttering

Sivan Jossinger1, Vered Kronfeld-Duenias1, Avital Zislis1, Ofer Amir2, Michal Ben-Shachar1;1Bar-Ilan University, 2Tel-Aviv University

The ability to produce speech is a key component of human cognition. One of the basic characteristics of speech production is speech rate, affecting the intelligibility, fluency, and communication efficiency of the speaker. Altered speech rate has been documented in various speech disorders, including persistent developmental stuttering. Specifically, adults who stutter (AWS) exhibit slower speech rate compared to fluent speakers (de Andrade et al. 2003). Evidence from fMRI implicates the cerebellum in the paced production of speech, in clinical and non-clinical populations (Ackermann 2008; Riecker et al. 2005). However, the cerebellar white matter pathways that communicate signals relevant for determining speaking rate remain unexplored. Here, we aim to assess the contribution of the cerebellar peduncles to speech rate in AWS and controls. Diffusion imaging data and speech rates were evaluated in 42 participants (23 AWS, 19 controls). The imaging data were acquired on a 3T General Electric scanner using diffusion weighted single shot EPI sequence (2 repetitions; b=1000 s/mm^2; 19 diffusion directions; ~2x2x2mm^3 resolution). Deterministic tractography was used to identify the superior, middle and inferior cerebral peduncles (SCP, MCP, ICP) bilaterally. Fractional anisotropy (FA), axial- and radial- diffusivity profiles were calculated along each tract and the resulting profiles were compared between the groups using Wilcoxon’s signed-rank test. Speech rate was measured over audio recordings of unstructured interviews, and quantified as the ratio between the total number of analyzed syllables and the time required for the participant to produce them (after excluding stuttered syllables from both measures). Spearman’s correlations were calculated between speech rate and diffusion measures along the tracts. We did not find significant differences between AWS and controls in the diffusivity values of the cerebellar peduncles. However, in AWS we found a significant negative association between speech rate and FA within the left ICP (r=-.6235, p<.05; family-wise error corrected). Controls did not show this correlation, and the coefficients calculated in the two groups differed significantly (Fisher’s Z=1.763, p<.05). Spearman’s partial correlations confirmed that the negative correlation observed in the left ICP of AWS maintained its significance after controlling for age, semantic or phonological fluency (p<.005), but not when controlling for stuttering severity (p>.05). Post-hoc analysis revealed that the association between the left ICP and speech rate, observed in AWS, is driven by radial, not axial, diffusivity. Finally, no significant correlations were detected with speech rate in the SCP and MCP of either group. Our findings support the role of the left ICP in mediating speech rate among AWS, but not in controls. The ICP is a major cerebellar pathway that transmits sensory feedback signals from the olivary nucleus into the cerebellum (Sokolov et al. 2017). It has been previously suggested that AWS rely too heavily on sensory feedback (Civier et al. 2010; Max et al. 2004), which can potentially lead to a reduction in speech rate, due to the slow nature of biological feedback loops. Together, our findings suggest a tentative but plausible neural mechanism for speech-rate reduction observed in AWS.

Topic Area: Speech Motor Control and Sensorimotor Integration

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