Myeloarchitectonic Asymmetries of Language Regions in the Human Brain

Brain evolution and language: A comparative 3D analysis of Wernicke's area in extant and fossil hominids

The spoken word does not fossilize. Despite this, scientists have long sought to unearth the origins of language within the human lineage. One of the lines of evidence they have pursued is functional brain areas, such as Broca's and Wernicke's areas, which are associated with speech production and comprehension, respectively. Sulcal layout of Broca's area clearly differs between humans and our closest living relatives, the chimpanzees, enabling its homolog in fossil hominins to be deemed more chimpanzee-like (i.e., closer to the ancestral form) or more human-like (i.e., derived form) with relative ease. Yet, no such differences have been found for Wernicke's area. This study compares sulcal and gyral organization of Wernicke's area across extant human brains (n=4), extant chimpanzee brains (n=5) and fossil hominin endocasts (n=4). Some chimpanzee brains had indications of leftward Wernicke's area asymmetry in the form of a shorter Sylvian fissure and/or caudal superior temporal gyral bulging in the left hemisphere. Overlap between the superior and middle temporal sulci in human but not chimpanzee brains may be due to a relatively larger Wernicke's area in humans. Fragmentation of the main body of the superior temporal sulcus exclusively in human left hemispheres was ascribed to a leftward Wernicke's area asymmetry in this species. Endocast examination found that, while Paranthropus robustus exhibit human-like overlap between the superior and middle temporal sulci, Australopithecus africanus do not, although they do exhibit chimpanzee-like caudal superior temporal gyral bulging. Such findings signal, albeit loosely, a more human-like Wernicke's area in Paranthropus than Australopithecus.

A whole-brain 3D myeloarchitectonic atlas: Mapping the Vogt-Vogt legacy to the cortical surface

Building precise and detailed parcellations of anatomically and functionally distinct brain areas has been a major focus in Neuroscience. Pioneer anatomists parcellated the cortical manifold based on extensive histological studies of post-mortem brain, harnessing local variations in cortical cyto- and myeloarchitecture to define areal boundaries. Compared to the cytoarchitectonic field, where multiple neuroimaging studies have recently translated this old legacy data into useful analytical resources, myeloarchitectonics, which parcellate the cortex based on the organization of myelinated fibers, has received less attention. Here, we present the neocortical surface-based myeloarchitectonic atlas based on the histology-derived maps of the Vogt-Vogt school and its 2D translation by Nieuwenhuys. In addition to a myeloarchitectonic parcellation, our package includes intracortical laminar profiles of myelin content based on Vogt-Vogt-Hopf original publications. Histology-derived myelin density mapped on our atlas demonstrated a close overlap with in vivo quantitative MRI markers for myelin and relates to cytoarchitectural features. Complementing the existing battery of approaches for digital cartography, the whole-brain myeloarchitectonic atlas offers an opportunity to validate imaging surrogate markers of myelin in both health and disease.

Air pollution associated with cognitive decline by the mediating effects of sleep cycle disruption and changes in brain structure in adults

The effects of air pollution on sleep and dementia remain unclear. The objective of this study was to investigate the effects of air pollution on cognitive function as mediated by the sleep cycle. A cross-sectional study design was conducted to recruit 4866 subjects on which PSG had been performed. Fifty of them were further given a cognitive function evaluation by the MMSE and CASI as well as brain images by CT and MRI. Associations of 1-year air pollution parameters with sleep parameters, cognitive function, and brain structure were examined. We observed that O₃ was associated with a decrease in arousal, an increase in the N1 stage, and a decrease in the N2 stage of sleep. NO₂ was associated with an increase in the N1 stage, a decrease in the N2 stage, and an increase in REM. PM_2.5 was associated with a decrease in the N1 stage, increases in the N2 and N3 stages, and a decrease in REM. The N1 and N2 stages were associated with cognitive decline, but REM was associated with an increase in cognitive function. The N1 stage was a mediator of the effects of PM_2.5 on the concentration domain of the MMSE. O₃ was associated with an increase in the pars orbitalis volume of the left brain. NO₂ was associated with increases in the rostral middle frontal volume, supramarginal gyrus volume, and transverse temporal volume of the left brain, and the pars opercularis volume of the right brain. PM_2.5 was associated with increases in the pars triangularis volume of the left brain and the fusiform thickness of the right brain. In conclusion, we observed that air pollution was associated with cognitive decline by mediating effects on the sleep cycle with changes in the brain structure in controlling executive, learning, and language functions in adults.

Are We Right about the Right TPJ? A Review of Brain Stimulation and Social Cognition in the Right Temporal Parietal Junction

In the past decade, the functional role of the TPJ (Temporal Parietal Junction) has become more evident in terms of its contribution to social cognition. Studies have revealed the TPJ as a ‘distinguisher’ of self and other with research focused on non-clinical populations as well as in individuals with Autism and Type I Schizophrenia. Further research has focused on the integration of self-other distinctions with proprioception. Much of what we now know about the causal role of the right TPJ derives from TMS (Transcranial Magnetic Stimulation), rTMS repetitive Transcranial Magnetic Stimulation), and tDCS (transcranial Direct Cortical Stimulation). In this review, we focus on the role of the right TPJ as a moderator of self, which is integrated and distinct from ‘other’ and how brain stimulation has established the causal relationship between the underlying cortex and agency.

Broca's area and the search for anatomical asymmetry: commentary and perspectives

We present a brief commentary on the field's search for an anatomical asymmetry between Broca's area and its homologue in the non-dominant hemisphere, focusing on a selection of studies, including research from the last decade. We demonstrate that, several years after the influential review of Keller and colleagues from 2009, and despite recent advances in neuroimaging, the existence of a structural asymmetry of Broca's area is still controversial. This is especially the case for studies of the macroanatomy of this region. We point out the inconsistencies in methodology across studies that could account for the discrepancy in results. Investigations of the microstructure of Broca's area show a trend of a leftward asymmetry, but it is still unclear how these results relate to language dominance. We suggest that it may be necessary to combine multiple metrics in a systematic manner to find robust asymmetries and to expand the regional scope of structural investigations. Finally, based on the current state of the literature, we should not rule out the possibility that language dominance may simply not be reflected in local anatomical differences in the brain.