Diffusion magnetic resonance imaging (dMRI) is commonly used to assess the tissue and cellular substructure of the human brain. In the white matter, myelinated axons are the principal neural elements ...that shape dMRI through the restriction of water diffusion; however, in the gray matter the relative contributions of myelinated axons and other tissue features to dMRI are poorly understood. Here we investigate the determinants of diffusion in the cerebral cortex. Specifically, we ask whether myelinated axons significantly shape dMRI fractional anisotropy (dMRI-FA), a measure commonly used to characterize tissue properties in humans. We compared ultra-high resolution ex vivo dMRI data from the brain of a marmoset monkey with both myelin- and Nissl-stained histological sections obtained from the same brain after scanning. We found that the dMRI-FA did not match the spatial distribution of myelin in the gray matter. Instead dMRI-FA was more closely related to the anisotropy of stained tissue features, most prominently those revealed by Nissl staining and to a lesser extent those revealed by myelin staining. Our results suggest that unmyelinated neurites such as large caliber apical dendrites are the primary features shaping dMRI measures in the cerebral cortex.
The temporal association cortex is considered a primate specialization and is involved in complex behaviors, with some, such as language, particularly characteristic of humans. The emergence of these ...behaviors has been linked to major differences in temporal lobe white matter in humans compared with monkeys. It is unknown, however, how the organization of the temporal lobe differs across several anthropoid primates. Therefore, we systematically compared the organization of the major temporal lobe white matter tracts in the human, gorilla, and chimpanzee great apes and in the macaque monkey. We show that humans and great apes, in particular the chimpanzee, exhibit an expanded and more complex occipital-temporal white matter system; additionally, in humans, the invasion of dorsal tracts into the temporal lobe provides a further specialization. We demonstrate the reorganization of different tracts along the primate evolutionary tree, including distinctive connectivity of human temporal gray matter.
Inspired by the dynamic clamp of cellular neuroscience, this paper introduces VPI -- Virtual Partner Interaction -- a coupled dynamical system for studying real time interaction between a human and a ...machine. In this proof of concept study, human subjects coordinate hand movements with a virtual partner, an avatar of a hand whose movements are driven by a computerized version of the Haken-Kelso-Bunz (HKB) equations that have been shown to govern basic forms of human coordination. As a surrogate system for human social coordination, VPI allows one to examine regions of the parameter space not typically explored during live interactions. A number of novel behaviors never previously observed are uncovered and accounted for. Having its basis in an empirically derived theory of human coordination, VPI offers a principled approach to human-machine interaction and opens up new ways to understand how humans interact with human-like machines including identification of underlying neural mechanisms.
We present a new 3D template atlas of the anatomical subdivisions of the macaque brain, which is based on and aligned to the magnetic resonance imaging (MRI) data set and histological sections of the ...Saleem and Logothetis atlas. We describe the creation and validation of the atlas that, when registered with macaque structural or functional MRI scans, provides a straightforward means to estimate the boundaries between architectonic areas, either in a 3D volume with different planes of sections, or on an inflated brain surface (cortical flat map). As such, this new template atlas is intended for use as a reference standard for macaque brain research. Atlases and templates are available as both volumes and surfaces in standard NIFTI and GIFTI formats.
This thesis concerns the cortical connectivity in Primates. The efficacy of Diffusion weighted MRI (dMRI) is examined. White matter (“WM”) systems subjacent to cortex (“superficial WM” ) are found to ...be a limiting factor to dMRI tractography. Superficial WM systems are examined with dMRI itself, and with analysis of histological data from the scanned brains. dMRI data was acquired ex-vivo at exceptional spatial and angular resolution (250μm in Rhesus, 150μm in Marmoset). The superficial WM was found to be complex, and with current dMRI methods, an effective barrier to tracking to and from around 50% of cortex in Rhesus. The quality of our data allowed Gray matter seeding, so that penetration both into and out of cortex was examined. We summarize the history of cortical connectivity and current work in tractography. We present an account of the formation and properties of the superficial WM. We compare tracking behaviors to tracer results, and develop a series of scalar maps on cortical surface models to summarize tracking behaviors. We attempt to explain these maps by examining the underlying tracking behavior and the brain tissue itself, revealing the intricate nature of the superficial WM. Chapter 4 contains a separate but related project in which a histologically accurate high resolution 3D and surface atlas of the Rhesus cortex is constructed with unprecedented accuracy. A method to rapidly and accurately non-linearly transform the atlas to a scan of another animal is developed, thus labelling its cortex. accuracy is by comparison to histology of the scanned animals.
This thesis concerns the cortical connectivity in Primates. The efficacy of Diffusion weighted MRI (dMRI) is examined. White matter (“WM”) systems subjacent to cortex (“superficial WM” ) are found to ...be a limiting factor to dMRI tractography. Superficial WM systems are examined with dMRI itself, and with analysis of histological data from the scanned brains. dMRI data was acquired ex-vivo at exceptional spatial and angular resolution (250μm in Rhesus, 150μm in Marmoset). The superficial WM was found to be complex, and with current dMRI methods, an effective barrier to tracking to and from around 50% of cortex in Rhesus. The quality of our data allowed Gray matter seeding, so that penetration both into and out of cortex was examined. We summarize the history of cortical connectivity and current work in tractography. We present an account of the formation and properties of the superficial WM. We compare tracking behaviors to tracer results, and develop a series of scalar maps on cortical surface models to summarize tracking behaviors. We attempt to explain these maps by examining the underlying tracking behavior and the brain tissue itself, revealing the intricate nature of the superficial WM. Chapter 4 contains a separate but related project in which a histologically accurate high resolution 3D and surface atlas of the Rhesus cortex is constructed with unprecedented accuracy. A method to rapidly and accurately non-linearly transform the atlas to a scan of another animal is developed, thus labelling its cortex. accuracy is by comparison to histology of the scanned animals.
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