Sexual Dimorphism Within Brain Regions Controlling Speech Production.

Laura De Lima Xavier,Kristina Simonyan,Sandra Hanekamp

doi:10.3389/fnins.2019.00795

Abstract

Neural processing of speech production has been traditionally attributed to the left hemisphere. However, it remains unclear if there are structural bases for speech functional lateralization and if these may be partially explained by sexual dimorphism of cortical morphology. We used a combination of high-resolution MRI and speech-production functional MRI to examine cortical thickness of brain regions involved in speech control in healthy males and females. We identified greater cortical thickness of the left Heschl’s gyrus in females compared to males. Additionally, rightward asymmetry of the supramarginal gyrus and leftward asymmetry of the precentral gyrus were found within both male and female groups. Sexual dimorphism of the Heschl’s gyrus may underlie known differences in auditory processing for speech production between males and females, whereas findings of asymmetries within cortical areas involved in speech motor execution and planning may contribute to the hemispheric localization of functional activity and connectivity of these regions within the speech production network. Our findings highlight the importance of consideration of sex as a biological variable in studies on neural correlates of speech control.

Highlights

Speech production is a complex motor behavior that requires the involvement of several brain regions and their respective networks, which collectively support different aspects of auditory and phonological processing, sensorimotor integration (SMG), executive function, motor planning and execution (Simonyan and Fuertinger, 2015)
Inconsistencies in findings might stem from high functional heterogeneity that characterizes large atlas-based macroanatomic labels as used in previous studies. To circumvent these limitations and to focus on the speech production system, we examined the presence of sex differences in cortical thickness (CT) in brain regions that are functionally active during real-life speech production in healthy males and females
Both males and females exhibited a typical pattern of cortical activity during speech production, which involved primary sensorimotor, premotor, inferior frontal, middle cingulate, auditory, inferior parietal and insular regions (Figure 2A), in agreement with other studies investigating speech production (e.g., Tourville and Guenther, 2003; Fuertinger et al, 2015; Simonyan et al, 2016; Basilakos et al, 2018; Kearney and Guenther, 2019)

Summary

INTRODUCTION

Speech production is a complex motor behavior that requires the involvement of several brain regions and their respective networks, which collectively support different aspects of auditory and phonological processing, sensorimotor integration (SMG), executive function, motor planning and execution (Simonyan and Fuertinger, 2015). Contrary to the empirical notion of left-hemispheric lateralization of brain activity during speech production, several recent studies defined a bilateral functional and structural distribution of the large-scale speech network (Simonyan et al, 2009; Morillon et al, 2010; Gehrig et al, 2012; Silbert et al, 2014; Simonyan and Fuertinger, 2015; Kumar et al, 2016). Inconsistencies in findings might stem from high functional heterogeneity that characterizes large atlas-based macroanatomic labels as used in previous studies To circumvent these limitations and to focus on the speech production system, we examined the presence of sex differences in cortical thickness (CT) in brain regions that are functionally active during real-life speech production in healthy males and females. We hypothesized that hemispheric lateralization of regional brain activity during speech production may, in part, be explained by sex-specific asymmetry in cortical morphology within the speech controlling network

MATERIALS AND METHODS

DISCUSSION

ETHICS STATEMENT