1,225 research outputs found
Censoring Distances Based on Labeled Cortical Distance Maps in Cortical Morphometry
Shape differences are manifested in cortical structures due to
neuropsychiatric disorders. Such differences can be measured by labeled
cortical distance mapping (LCDM) which characterizes the morphometry of the
laminar cortical mantle of cortical structures. LCDM data consist of signed
distances of gray matter (GM) voxels with respect to GM/white matter (WM)
surface. Volumes and descriptive measures (such as means and variances) for
each subject and the pooled distances provide the morphometric differences
between diagnostic groups, but they do not reveal all the morphometric
information contained in LCDM distances. To extract more information from LCDM
data, censoring of the distances is introduced. For censoring of LCDM
distances, the range of LCDM distances is partitioned at a fixed increment
size; and at each censoring step, and distances not exceeding the censoring
distance are kept. Censored LCDM distances inherit the advantages of the pooled
distances. Furthermore, the analysis of censored distances provides information
about the location of morphometric differences which cannot be obtained from
the pooled distances. However, at each step, the censored distances aggregate,
which might confound the results. The influence of data aggregation is
investigated with an extensive Monte Carlo simulation analysis and it is
demonstrated that this influence is negligible. As an illustrative example, GM
of ventral medial prefrontal cortices (VMPFCs) of subjects with major
depressive disorder (MDD), subjects at high risk (HR) of MDD, and healthy
control (Ctrl) subjects are used. A significant reduction in laminar thickness
of the VMPFC and perhaps shrinkage in MDD and HR subjects is observed when
compared to Ctrl subjects. The methodology is also applicable to LCDM-based
morphometric measures of other cortical structures affected by disease.Comment: 25 pages, 10 figure
Disentangling causal webs in the brain using functional Magnetic Resonance Imaging: A review of current approaches
In the past two decades, functional Magnetic Resonance Imaging has been used
to relate neuronal network activity to cognitive processing and behaviour.
Recently this approach has been augmented by algorithms that allow us to infer
causal links between component populations of neuronal networks. Multiple
inference procedures have been proposed to approach this research question but
so far, each method has limitations when it comes to establishing whole-brain
connectivity patterns. In this work, we discuss eight ways to infer causality
in fMRI research: Bayesian Nets, Dynamical Causal Modelling, Granger Causality,
Likelihood Ratios, LiNGAM, Patel's Tau, Structural Equation Modelling, and
Transfer Entropy. We finish with formulating some recommendations for the
future directions in this area
Structure Learning in Coupled Dynamical Systems and Dynamic Causal Modelling
Identifying a coupled dynamical system out of many plausible candidates, each
of which could serve as the underlying generator of some observed measurements,
is a profoundly ill posed problem that commonly arises when modelling real
world phenomena. In this review, we detail a set of statistical procedures for
inferring the structure of nonlinear coupled dynamical systems (structure
learning), which has proved useful in neuroscience research. A key focus here
is the comparison of competing models of (ie, hypotheses about) network
architectures and implicit coupling functions in terms of their Bayesian model
evidence. These methods are collectively referred to as dynamical casual
modelling (DCM). We focus on a relatively new approach that is proving
remarkably useful; namely, Bayesian model reduction (BMR), which enables rapid
evaluation and comparison of models that differ in their network architecture.
We illustrate the usefulness of these techniques through modelling
neurovascular coupling (cellular pathways linking neuronal and vascular
systems), whose function is an active focus of research in neurobiology and the
imaging of coupled neuronal systems
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The ASD Living Biology: from cell proliferation to clinical phenotype.
Autism spectrum disorder (ASD) has captured the attention of scientists, clinicians and the lay public because of its uncertain origins and striking and unexplained clinical heterogeneity. Here we review genetic, genomic, cellular, postmortem, animal model, and cell model evidence that shows ASD begins in the womb. This evidence leads to a new theory that ASD is a multistage, progressive disorder of brain development, spanning nearly all of prenatal life. ASD can begin as early as the 1st and 2nd trimester with disruption of cell proliferation and differentiation. It continues with disruption of neural migration, laminar disorganization, altered neuron maturation and neurite outgrowth, disruption of synaptogenesis and reduced neural network functioning. Among the most commonly reported high-confidence ASD (hcASD) genes, 94% express during prenatal life and affect these fetal processes in neocortex, amygdala, hippocampus, striatum and cerebellum. A majority of hcASD genes are pleiotropic, and affect proliferation/differentiation and/or synapse development. Proliferation and subsequent fetal stages can also be disrupted by maternal immune activation in the 1st trimester. Commonly implicated pathways, PI3K/AKT and RAS/ERK, are also pleiotropic and affect multiple fetal processes from proliferation through synapse and neural functional development. In different ASD individuals, variation in how and when these pleiotropic pathways are dysregulated, will lead to different, even opposing effects, producing prenatal as well as later neural and clinical heterogeneity. Thus, the pathogenesis of ASD is not set at one point in time and does not reside in one process, but rather is a cascade of prenatal pathogenic processes in the vast majority of ASD toddlers. Despite this new knowledge and theory that ASD biology begins in the womb, current research methods have not provided individualized information: What are the fetal processes and early-age molecular and cellular differences that underlie ASD in each individual child? Without such individualized knowledge, rapid advances in biological-based diagnostic, prognostic, and precision medicine treatments cannot occur. Missing, therefore, is what we call ASD Living Biology. This is a conceptual and paradigm shift towards a focus on the abnormal prenatal processes underlying ASD within each living individual. The concept emphasizes the specific need for foundational knowledge of a living child's development from abnormal prenatal beginnings to early clinical stages. The ASD Living Biology paradigm seeks this knowledge by linking genetic and in vitro prenatal molecular, cellular and neural measurements with in vivo post-natal molecular, neural and clinical presentation and progression in each ASD child. We review the first such study, which confirms the multistage fetal nature of ASD and provides the first in vitro fetal-stage explanation for in vivo early brain overgrowth. Within-child ASD Living Biology is a novel research concept we coin here that advocates the integration of in vitro prenatal and in vivo early post-natal information to generate individualized and group-level explanations, clinically useful prognoses, and precision medicine approaches that are truly beneficial for the individual infant and toddler with ASD
Chromatin organizer CTCF in brain development and behaviour
Chromatin architecture is an important regulator of gene expression, which dictates development. Mutations in one copy of the CTCF chromatin organizer gene cause intellectual disability and autism. Polymorphisms in CTCF have also been associated with increased risk for schizophrenia, a condition that overlaps in biological etiology with autism and intellectual disability. In this thesis, we sought to understand the role of CTCF in neurodevelopment using brain-specific conditional knockout and heterozygote mouse models. Using the Ctcf-null animals, we identify a cell-autonomous role for CTCF in regulating cortical interneuron development in the medial ganglionic eminence (MGE) through the transcriptional control of Lhx6. In the absence of CTCF, MGE-derived cortical interneuron subtypes are inappropriately specified such that their cortical laminar position is altered and there is a reduction in the number of cells expressing PV and SST. These features are rescued with viral-mediated re-expression of Lhx6. In addition, there is a concomitant increase in the expression of Lhx8, which specifies ventral telencephalic cell types in the MGE, indicating CTCF is an important regulator of cell fate choice in the MGE. To model the human condition associated with CTCF mutation, we generated mice heterozygous for Ctcf deletion in the developing brain (CtcfNestinHet). These mice had spontaneous hyperactivity and impaired spatial learning on behavioural testing. In addition to these behaviours, male mice had decreased sociability, altered aggression, and decreased anxiety. Together, this constellation of behaviours is reminiscent of other mouse models of schizophrenia, autism and intellectual disability. In addition, structural MRI revealed that CtcfNestinHet mouse brains had decreased white matter volume, suggestive of hypoconnectivity, a feature commonly attributed to the pathophysiology of autism. There were also significant volume decreases in the cerebellar nuclei, and an increase in the anterior cerebellar lobe. These findings provide further evidence for the emerging role of the cerebellum in cognition and in neurodevelopmental disorders. In summary, this work addresses the consequence of reduced CTCF expression in the developing brain at cellular, structural and behaviour levels, and thus significantly furthers our understanding of chromatin architecture regulation in neurodevelopmental disease
Neurovascular coupling: insights from multi-modal dynamic causal modelling of fMRI and MEG
This technical note presents a framework for investigating the underlying
mechanisms of neurovascular coupling in the human brain using multi-modal
magnetoencephalography (MEG) and functional magnetic resonance (fMRI)
neuroimaging data. This amounts to estimating the evidence for several
biologically informed models of neurovascular coupling using variational
Bayesian methods and selecting the most plausible explanation using Bayesian
model comparison. First, fMRI data is used to localise active neuronal sources.
The coordinates of neuronal sources are then used as priors in the
specification of a DCM for MEG, in order to estimate the underlying generators
of the electrophysiological responses. The ensuing estimates of neuronal
parameters are used to generate neuronal drive functions, which model the pre
or post synaptic responses to each experimental condition in the fMRI paradigm.
These functions form the input to a model of neurovascular coupling, the
parameters of which are estimated from the fMRI data. This establishes a
Bayesian fusion technique that characterises the BOLD response - asking, for
example, whether instantaneous or delayed pre or post synaptic signals mediate
haemodynamic responses. Bayesian model comparison is used to identify the most
plausible hypotheses about the causes of the multimodal data. We illustrate
this procedure by comparing a set of models of a single-subject auditory fMRI
and MEG dataset. Our exemplar analysis suggests that the origin of the BOLD
signal is mediated instantaneously by intrinsic neuronal dynamics and that
neurovascular coupling mechanisms are region-specific. The code and example
dataset associated with this technical note are available through the
statistical parametric mapping (SPM) software package
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