Microstructural asymmetries of the planum temporale predict functional lateralization of auditory-language processing

Abstract

Structural hemispheric asymmetry has long been assumed to guide functional asymmetry of the human brain, but empirical evidence for this compelling hypothesis remains scarce. Recently, it has been suggested that microstructural asymmetries may be more relevant to functional asymmetries than macrostructural asymmetries. To investigate the link between microstructure and function, we analyzed multimodal MRI data in 907 participants. We quantified structural and functional asymmetries of the planum temporale (PT), a cortical area crucial for auditory-language processing. We found associations of functional PT asymmetries and several microstructural asymmetries, such as intracortical myelin content, neurite density, and neurite orientation dispersion. The PT microstructure per se also showed hemispheric-specific coupling with PT functional activity. All these functional-structural associations are highly specific to within-PT functional activity during auditory-language processing. These results suggest that structural asymmetry guides functional lateralization of the same brain area and highlight a critical role of microstructural PT asymmetries in auditory-language processing.

Morphometrical asymmetries and tractography of speech-relevant cortex in relation to language lateralisation and rapid temporal processing

“…The exploratory analyses of the present study did not show a relationship of PT thickness asymmetry with behavioural RTP ability as measured by GDT, nor language lateralisation as measured by the DLT. This aligns with Qin et al [27] who found a significant positive relationship of PT surface area, but not thickness with lateralisation of PT activity (measured via fMRI) in a speech comprehension task. Leftward thickness asymmetry has been linked with processing of longer-temporal window cues [i.e., rightward biased under the AST; 69].…”

“…Use of developing automatic surface-based sub-segmentation software [e.g., 172] may allow more specific analyses of the asymmetry of these PT sub-regions and their involvement in speech-related lateralisation. Furthermore, as emphasised by Qin and colleagues [27] microstructural asymmetries of the PT (intracortical myelin, content, neurite density, & neurite orientation dispersion) also show relationships with functional lateralisation for speech-processing. Although these authors claim microstructure factors to be superior variables of interest, their results also showed micro/macro to be differentially sensitive to morphological variances – a finding that we suggest is strongly meriting of conjunctive use and exploration of both microstructure and macrostructure.…”

“…Here, morphometrical and connective both refer to structural measures: physical properties of the brain obtained with magnetic resonance imaging (MRI). The planum temporale is the emphasised due to being the foremost regionof-interest (ROI) in studies of lateralisation of speech [24][25][26][27]. Surface area is emphasised as the primary variable of interest to likewise adhere to extant trends in the literature [28,29].…”

“…Qin and colleages [27] assessed PT macrostructural (surface area and thickness) and microstructural (myelin content, neurite density, and neurite orientation dispersion) properties of the PT with functional lateralisation (measured using functional MRI) in speech perception and comprehension tasks. The authors reported a significant positive relationship of PT surface area (but not thickness) with lateralisation of speech comprehension.…”