Functional Parcellation Of Human Middle Temporal Gyrus And Its Applications To Autism Spectrum Disorders

The middle temporal gyrus(MTG)is located between the superior temporal sulcus and the inferior temporal sulcus,which plays an important role in the brain functions.Many papers have demonstrated that the MTG is not only involved in language processing,such as semantic processing,semantic cognition,word generation,vocabulary integration,and sentence cognition,but also associated with movement observation,scene investigation,deductive reasoning,and dynamic facial expression.Given its various functions,different sub-regions of MTG might be existed to response for different functions.However,most papers only referred MTG to anterior MTG and/or posterior MTG,leaving its boundary largely unknown.Therefore,delineating functional specialization of MTG is crucial for clinical neurosurgery and treatment associated with this area.However,to date,the parcellation results of MTG were controversial.Most previous sub-regions of MTG were based on myelo-architectonic properties,anatomical observations of the sulci or gyri,which can only represent the local architectonic information rather than global connectivity patterns.Moreover,these methods can not be performed in vivo,limiting its evolution largely.Although the MTG has been parcellated into sub-regions with distinguished anatomical connectivity patterns,whether the structural topography of MTG can inform functional segregations of this area remains largely unknown.Accumulating evidence suggests that the brain's underlying organization and function can be directly and effectively delineated with resting-state functional connectivity(RSFC)by identifying putative functional boundaries between cortical areas.Therefore,we used RSFC profiles and coactivity-based parcellation to explore functional segregations of the MTG and demonstrate a brain atlas of MTG,which is appropriate for brain imaging research.In the currents study,three important results need to be addressed:1.RSFC profiles were used to explore functional segregations of the MTG and defined four sub-regions from anterior to posterior in two independent datasets,which showed a similar pattern to MTG parcellation scheme obtained using anatomical connectivity.The functional segregations of MTG were further supported by whole brain RSFC,co-activation,specific RFSC,and co-activation mapping.Furthermore,the fingerprint with predefined 10 networks and functional characterizations of each sub-region using meta-analysis also identified functional distinction between sub-regions.The specific connectivity analysis and functional characterization indicated that the bilateral most anterior sub-regions mainly participated in social cognition and semantic processing;the ventral middle sub-regions were involved in social cognition in left hemisphere and auditory processing in right hemisphere;the bilateral ventro-posterior sub-regions participated in action observation,whereas the left sub-region was also involved in semantic processing;both of the dorsal sub-regions in superior temporal sulcus were involved in language,social cognition,and auditory processing.Taken together,our findings demonstrated MTG shares similar structural and functional topographies and provide more detailed information about the functional organization of the MTG,which may facilitate future clinical and cognitive research on this area.2.We first performed connectivity-based parcellation using the BrainMap database to identify fine-grained functional topography of the MTG.Then,the MTG sub-regions were used to investigate differences in the functional connectivity in children and adults with ASD using two data sets from Autism Brain Imaging Data Exchange database.Four distinct sub-regions in the human left and right MTG were identified,including the anterior MTG(aMTG),middle-anterior MTG(maMTG),middle-posterior MTG,and posterior MTG(pMTG).The bilateral pMTG was more vulnerable in both children and adults with ASD than in the typically developing(TD)group,mainly showing hypo-connectivity with different brain regions.In addition,the bilateral aMTG and right maMTG also showed altered functional connectivity in adults with ASD compared to the TD group.Moreover,all these altered MTG sub-regions were mainly associated with social cognition and language,as revealed by functional characterization.Further correlation analyses also showed trends of association between altered connectivity of the left aMTG and the Autism Diagnostic Observation Schedule scores in adults with ASD.Together,these results suggest a potential objective way to explore sub-regional differences associated with such disorders.3.We combined T1 images and structural covariance network to investigate the differences in gray matter volume and structural strength of MTG sub-regions in children and adults with ASD using two data sets from Autism Brain Imaging Data Exchange database.We found that the gray matter volume in the left aMTG and left pMTG were significantly increased in the children with ASD compared to normal controls,while the gray matter volume of left pMTG was significantly decreased in adults with ASD compared to normal controls.Correlation analyses revealed that these changes were associated with scores of social communication,social interaction,and behavior in the ASD.Gray matter volume based structural covariance network showed no significant changes in structural strength of MTG sub-regions in children with ASD,but showed significantly decreased structural strength between right pMTG and right cerebellum in the adults with ASD.These results demonstrated that MTG sub-regions might play different roles in the children and adults with ASD.Thus,it is important and necessary to investigate the functional and structural connectivity at sub-regional level.