Comprehensive mapping of the thalamic commissures in the rodent brain.

Brain commissures are antiparallel white matter fiber bundles that connect both hemispheres across the midsagittal plane at different anatomical levels. In the mammalian brain, the best-known commissures are the corpus callosum, the anterior and the posterior commissures. Recent studies have identified a new white matter pathway, the thalamic commissures (TCs), that connect the cortex to the contralateral thalamus in rodents and primates.

An open access resource for marmoset neuroscientific apparatus.

The use of the common marmoset () for neuroscientific inquiry has grown precipitously over the past two decades. Despite windfalls of grant support from funding initiatives in North America, Europe, and Asia to model human brain diseases in the marmoset, marmoset-specific apparatus are of sparse availability from commercial vendors and thus are often developed and reside within individual laboratories. Through our collective research efforts, we have designed and vetted myriad designs for awake or anesthetized magnetic resonance imaging (MRI), positron emission tomography (PET), computed tomography (CT), as well as focused ultrasound (FUS), electrophysiology, optical imaging, surgery, and behavior in marmosets across the age-span.

Random Effects Models for Understanding Variability and Association between Brain Functional and Structural Connectivity.

The human brain is organized as a complex network, where connections between regions are characterized by both functional connectivity (FC) and structural connectivity (SC). While previous studies have primarily focused on network-level FC-SC correlations (i.e.

MRI and non-MRI quantifiable neuroanatomical and functional parameters are useful for tractography.

Tractography provides a powerful framework to reconstruct white matter pathways from diffusion magnetic resonance imaging (dMRI) but remains challenged by its inherent ambiguity and lack of direct biological specificity. This short communication summarizes the key points of a debate held at the 2024 Tract-Anat Retreat on the utility of MRI and non-MRI quantifiable neuroanatomical and functional parameters for improving tractography. During the discussion, concerns were raised about the availability of histological properties only on post-mortem tissues, the disparity in scale between MRI and other modalities and the additional costs (both in time and money) of such additional parameters.

Brain connectivity: complex, not chaotic.

The term "connections" is a commonly used and convenient shorthand for describing the complex organization of the brain, but it can easily lead to an overemphasis on pairwise or point-to-point, source-target network connectivity. Anatomical studies make clear that there are other important features to consider such as divergence and collateralization (axons or bundles branching to multiple targets), convergence (multiple bundles from different sources converging on the same target), and scrambled topography along a trajectory. This short "Did You Know" communication elaborates on several of these features from the anatomical perspective, while inviting continued dialogue with the tractography community in addressing the shared goals of better understanding brain organization.

Analysis of functional connectivity changes from childhood to old age: A study using HCP-D, HCP-YA, and HCP-A datasets.

We present a new clustering-enabled regression approach to investigate how functional connectivity (FC) of the entire brain changes from childhood to old age. By applying this method to resting-state functional magnetic resonance imaging data aggregated from three Human Connectome Project studies, we cluster brain regions that undergo identical age-related changes in FC and reveal diverse patterns of these changes for different region clusters. While most brain connections between pairs of regions show minimal yet statistically significant FC changes with age, only a tiny proportion of connections exhibit practically significant age-related changes in FC.

Brain Connectivity, Neural Networks, and Resilience in Aging and Neurodegeneration.

The importance of complex systems has become increasingly evident in recent years. The nervous system is one such example, with neural networks sitting at the intersection of complex networks and biology. A particularly exciting feature is the resilience of complex systems.

Noninvasive focal transgene delivery with viral neuronal tracers in the marmoset monkey.

We establish a reliable method for selectively delivering adeno-associated viral vectors (AAVs) across the blood-brain barrier (BBB) in the marmoset without the need for neurosurgical injection. We focally perturbed the BBB (∼1 × 2 mm) in area 8aD of the frontal cortex in four adult marmoset monkeys using low-intensity transcranial focused ultrasound aided by microbubbles. Within an hour of opening the BBB, either AAV2 or AAV9 was delivered systemically via tail-vein injection.

Direct interhemispheric cortical communication via thalamic commissures: a new white matter pathway in the primate brain.

Cortical neurons of eutherian mammals project to the contralateral hemisphere, crossing the midline primarily via the corpus callosum and the anterior, posterior, and hippocampal commissures. We recently reported and named the thalamic commissures (TCs) as an additional interhemispheric axonal fiber pathway connecting the cortex to the contralateral thalamus in the rodent brain. Here, we demonstrate that TCs also exist in primates and characterize the connectivity of these pathways with high-resolution diffusion-weighted MRI, viral axonal tracing, and fMRI.

Direct interhemispheric cortical communication via thalamic commissures: a new white-matter pathway in the primate brain.

Cortical neurons of eutherian mammals project to the contralateral hemisphere, crossing the midline primarily via the corpus callosum and the anterior, posterior, and hippocampal commissures. We recently reported an additional commissural pathway in rodents, termed the thalamic commissures (TCs), as another interhemispheric axonal fiber pathway that connects cortex to the contralateral thalamus. Here, we demonstrate that TCs also exist in primates and characterize the connectivity of these pathways with high-resolution diffusion-weighted magnetic resonance imaging, viral axonal tracing, and functional MRI.

Heterotopic connectivity of callosal dysgenesis in mice and humans.

The corpus callosum (CC), the largest brain commissure and the primary white matter pathway for interhemispheric cortical connectivity, was traditionally viewed as a predominantly homotopic structure, connecting mirror areas of the cortex. However, new studies verified that most callosal commissural fibers are heterotopic. Recently, we reported that ~75% of the callosal connections in the brains of mice, marmosets, and humans are heterotopic, having an essential role in determining the global properties of brain networks.

An integrated resource for functional and structural connectivity of the marmoset brain.

Comprehensive integration of structural and functional connectivity data is required to model brain functions accurately. While resources for studying the structural connectivity of non-human primate brains already exist, their integration with functional connectivity data has remained unavailable. Here we present a comprehensive resource that integrates the most extensive awake marmoset resting-state fMRI data available to date (39 marmoset monkeys, 710 runs, 12117 mins) with previously published cellular-level neuronal tracing data (52 marmoset monkeys, 143 injections) and multi-resolution diffusion MRI datasets.

The relevance of heterotopic callosal fibers to interhemispheric connectivity of the mammalian brain.

The corpus callosum (CC) is the largest white matter structure and the primary pathway for interhemispheric brain communication. Investigating callosal connectivity is crucial to unraveling the brain's anatomical and functional organization in health and disease. Classical anatomical studies have characterized the bulk of callosal axonal fibers as connecting primarily homotopic cortical areas.

An open access resource for functional brain connectivity from fully awake marmosets.

The common marmoset (Callithrix jacchus) is quickly gaining traction as a premier neuroscientific model. However, considerable progress is still needed in understanding the functional and structural organization of the marmoset brain to rival that documented in longstanding preclinical model species, like mice, rats, and Old World primates. To accelerate such progress, we present the Marmoset Functional Brain Connectivity Resource (marmosetbrainconnectome.

Corpus callosum dysgenesis causes novel patterns of structural and functional brain connectivity.

Developmental malformations (dysgenesis) of the corpus callosum lead to neurological conditions with a broad range of clinical presentations. Investigating the altered brain connectivity patterns is crucial to understanding both adaptive and maladaptive neuroplasticity in corpus callosum dysgenesis patients. Here, we acquired structural diffusion-weighted and resting-state functional MRI data from a cohort of 11 corpus callosum dysgenesis patients (five with agenesis and six with hypoplasia) and compared their structural and functional connectivity patterns to healthy subjects selected from the Human Connectome Project.

Direct Interhemispheric Cortical Communication via Thalamic Commissures: A New White-Matter Pathway in the Rodent Brain.

The corpus callosum (CC), the anterior (AC), and the posterior (PC) commissures are the principal axonal fiber bundle pathways that allow bidirectional communication between the brain hemispheres. Here, we used the Allen mouse brain connectivity atlas and high-resolution diffusion-weighted MRI (DWI) to investigate interhemispheric fiber bundles in C57bl6/J mice, the most commonly used wild-type mouse model in biomedical research. We identified 1) commissural projections from the primary motor area through the AC to the contralateral hemisphere; and 2) intrathalamic interhemispheric fiber bundles from multiple regions in the frontal cortex to the contralateral thalamus.

Dynamic Interhemispheric Desynchronization in Marmosets and Humans With Disorders of the Corpus Callosum.

The corpus callosum, the principal structural avenue for interhemispheric neuronal communication, controls the brain's lateralization. Developmental malformations of the corpus callosum (CCD) can lead to learning and intellectual disabilities. Currently, there is no clear explanation for these symptoms.

Marmoset Brain Mapping V3: Population multi-modal standard volumetric and surface-based templates.

The standard anatomical brain template provides a common space and coordinate system for visualizing and analyzing neuroimaging data from large cohorts of subjects. Previous templates and atlases for the common marmoset brain were either based on data from a single individual or lacked essential functionalities for neuroimaging analysis. Here, we present new population-based in-vivo standard templates and tools derived from multi-modal data of 27 marmosets, including multiple types of T1w and T2w contrast images, DTI contrasts, and large field-of-view MRI and CT images.

Ultrahigh-resolution MRI Reveals Extensive Cortical Demyelination in a Nonhuman Primate Model of Multiple Sclerosis.

Cortical lesions are a primary driver of disability in multiple sclerosis (MS). However, noninvasive detection of cortical lesions with in vivo magnetic resonance imaging (MRI) remains challenging. Experimental autoimmune encephalomyelitis (EAE) in the common marmoset is a relevant animal model of MS for investigating the pathophysiological mechanisms leading to brain damage.

Long-distance aberrant heterotopic connectivity in a mouse strain with a high incidence of callosal anomalies.

Corpus callosum dysgenesis (CCD) is a developmental brain condition in which some white matter fibers fail to find their natural course across the midplane, reorganizing instead to form new aberrant pathways. This type of white matter reorganization is known as long-distance plasticity (LDP). The present work aimed to characterize the Balb/c mouse strain as a model of CCD.

A resource for the detailed 3D mapping of white matter pathways in the marmoset brain.

While the fundamental importance of the white matter in supporting neuronal communication is well known, existing publications of primate brains do not feature a detailed description of its complex anatomy. The main barrier to achieving this is that existing primate neuroimaging data have insufficient spatial resolution to resolve white matter pathways fully. Here we present a resource that allows detailed descriptions of white matter structures and trajectories of fiber pathways in the marmoset brain.

Anatomical and functional investigation of the marmoset default mode network.

The default mode network (DMN) is associated with a wide range of brain functions. In humans, the DMN is marked by strong functional connectivity among three core regions: medial prefrontal cortex (mPFC), posterior parietal cortex (PPC), and the medial parietal and posterior cingulate cortex (PCC). Neuroimaging studies have shown that the DMN also exists in non-human primates, suggesting that it may be a conserved feature of the primate brain.

The Absolute Number of Oligodendrocytes in the Adult Mouse Brain.

The central nervous system is a highly complex network composed of various cell types, each one with different subpopulations. Each cell type has distinct roles for the functional operation of circuits, and ultimately, for brain physiology in general. Since the absolute number of each cell type is considered a proxy of its functional complexity, one approach to better understand how the brain works is to unravel its absolute cellularity and the quantitative relations between cell populations; in other words, how one population of cells is quantitatively structured, in relation to another.

Perinatal Asphyxia and Brain Development: Mitochondrial Damage Without Anatomical or Cellular Losses.

Perinatal asphyxia remains a significant cause of neonatal mortality and is associated with long-term neurodegenerative disorders. In the present study, we evaluated cellular and subcellular damages to brain development in a model of mild perinatal asphyxia. Survival rate in the experimental group was 67%.