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At least 793 records · Page 44Linked to original sources
PubMed2004

Cultural evolution as a possible triggering or causative factor of common baldness.

Common baldness (alopecia) increasingly affects a higher number of individuals at earlier ages, independently of gender. One of the reasons could be lack of knowledge concerning its etiology. The human being has evolved to become a naked monkey, although there is no apparent reason to continue the evolutionary process up to becoming a bald monkey. According to this theory, common baldness is a degenerative process derived from certain inadequate cultural practices, such as excessive hair cutting or certain types of haircuts that prevent contact among hairs themselves and limit outside contact in ways that would alleviate balding. Blocking the flow of sebum towards the base of the hair follicle - and so interfering with the arrival of the stem cells to the dermal papilla with consequent hair miniaturization - ends up being the first negative physiological effect derived from certain cultural habits. As time goes by, other mechanisms become altered, which leads to a less and less reversibility of the process.

Alopecia↗
PubMed2004

A possible interdependency between the wavy path of enamel rods, distances of Retzius lines, and mitotic activity at the cervical loop in human teeth: a hypothesis.

In human enamel, the enamel rods do not run straight in most regions. Instead, they obtain an undulated path. The diameter of the enamel rods remains constant all the way, and a wavy pattern is necessary to produce the volume of the enamel mantle. It is not understood, how this undulated migration of ameloblasts is created. Considerations are presented to explain causal interdependencies between the wavy path of the enamel rods, unequal growth of the cervical loop cells and unequal distances of the striae of Retzius. To test these considerations, further research must record mitotic activity at the cervical loop during the stages of dental development. The distances of Retzius lines must be measured at different spots all over the whole enamel mantle, preferably in 3D. As a result, knowledge of the interdependency between the inner structure and the outer form of each tooth crown will lead to an understanding of tooth form and occlusion.

Ameloblasts↗
PubMed2005

Hypoplastic left heart syndrome: Rheumatic heart disease of the fetus?

Hypoplastic left heart syndrome (HLHS) accounts for nearly 25% of deaths among neonates with congenital heart disease. The essential feature of HLHS is a small left ventricle (LV) incapable of supporting the circulation. The etiology of HLHS is unknown. A hypothesis is proposed implicating an immune mechanism involving maternal antibodies produced in response to pharyngitis caused by group A beta-hemolytic streptococci (GABHS) ("strep throat"). After crossing the placenta, the antibodies injure the developing fetal heart, leading to HLHS either because of direct injury to the LV or secondary to reduced blood flow through affected aortic and mitral valves. Analogy is drawn to rheumatic heart disease (RHD), a known sequela of strep throat. In RHD a misdirected immune response originally intended for GABHS leads to cardiac injury through "molecular mimicry"; the normal heart antigens supposedly mimic the GABHS antigens. A similar pathogenesis is proposed for HLHS and related heart defects. HLHS may represent an extreme form of injury, while a milder insult may present as only mild aortic stenosis or a bicuspid aortic valve, conditions with wide prevalence among the general population. The injury may indeed superimpose on many other congenital heart defects, leading to a variable presentation of these other diseases. Beside remarkable likenesses between HLHS and RHD, the hypothesis is also supported by increasing evidence for the role of deleterious transplacental antibodies in the pathogenesis of other fetal diseases. Implications for other congenital heart diseases and the broader picture of global public health are discussed.

Female↗
PubMed2006

Topical botulinum toxin to treat hyperhidrosis? No sweat!

Palmar, plantar and axillary hyperhidrosis, though benign, may be burdensome and occupationally restrictive, even hazardous. Treatment modalities range from topical antiperspirants, iontophoresis, systemic medications such as anticholinergics and benzodiazepines and injections of botulinum toxin, to thoracic sympathectomy. Intradermal injections of botulinum toxin (BTX), though effective, are painful especially when multiple injections are required. Iontophoretic administration of BTX has been described, the BTX entering the eccrine sweat glands via the sweat pores and through the sweat ducts. We postulate that BTX can be administered topically, either unassisted or assisted by application of an electrical gradient, low-frequency ultrasound or excipients such as dimethylsulfoxide. We examine the rationale and feasibility for such a treatment modality and route of administration.

Administration, Topical↗
PubMed2006

Tropical enteropathy protects against Western diseases in environments of poor sanitation.

This hypothesis suggests that tropical enteropathy protects against Western diseases in environments of poor sanitation, and that the absence of tropical enteropathy contributes to the increased incidence of Western diseases in settings of improved sanitation. The hypothesis is supported by four observations: (1) The prevalence of tropical enteropathy is inversely related to the incidence of Western diseases, (2) The bowel is a major immune and neuroendocrine organ, and inflammation of the gut results in profound local and systemic changes, (3) Tropical enteropathy can account for the subtle clinical differences observed between individuals living in third world environments and industrialized societies, and (4) The concept that tropical enteropathy protects against Western diseases in environments of poor sanitation is consistent with the observations upon which the "Hygiene and Fetal Origins Hypotheses" are based. Identifying tropical enteropathy as a mechanism that protects against Western diseases in environments of poor sanitation creates a new testable hypothesis for some of the most common non-communicable diseases of industrialized societies.

Developed Countries↗
PubMedDate not supplied

Development of a 4-D digital mouse phantom for molecular imaging research.

PURPOSE: We develop a realistic and flexible 4-D digital mouse phantom and investigate its usefulness in molecular imaging research. METHODS: Organ shapes were modeled with non-uniform rational B-spline (NURBS) surfaces based on high-resolution 3-D magnetic resonance microscopy (MRM) data. Cardiac and respiratory motions were modeled based on gated magnetic resonance imaging (MRI) data obtained from normal mice. Pilot simulation studies in single-photon emission computed tomography (SPECT) and X-ray computed tomography (CT) were performed to demonstrate the utility of the phantom. RESULTS: NURBS are an efficient and flexible way to accurately model the anatomy and cardiac and respiratory motions for a realistic 4-D digital mouse phantom. The phantom is capable of producing realistic molecular imaging data from which imaging devices and techniques can be evaluated. CONCLUSION: The phantom provides a unique and useful tool in molecular imaging research. It can be used in the development of new imaging instrumentation, image acquisition strategies, and image processing and reconstruction methods.

Animals↗
PubMed2004

A 3D numerical study of the effect of channel height on leukocyte deformation and adhesion in parallel-plate flow chambers.

The effect of channel height on leukocyte adhesion to a lower plate in a parallel-plate flow chamber is studied by direct numerical simulations in three dimensions. The numerical model takes into account deformability and viscoelasticity of the leukocyte, membrane ruffles (microvilli), and the presence of mechanically different regions inside the cell (nucleus and cytoplasm). Leukocyte adhesion is assumed to be mediated by interactions of adhesion molecules on the tips of microvilli with their counterparts on the lower plate. Results of this study indicate that an adherent leukocyte experiences much less drag than a rigid sphere due to its deformation and transient stress growth. While overall leukocyte deformation is modest at shear stresses encountered in the microcirculation, deformation in the contact region is significant. At fixed wall shear stress, the contact area of the cell membrane with the substrate increases with increasing the ratio of cell diameter to channel height, leading to greater adhesion. This suggests that in vitro flow chamber studies typically underestimate leukocyte adhesion that occurs in the microcirculation.

Animals↗
PubMed2003

Normal and pathological reading: converging data from lesion and imaging studies.

In this paper we discuss cognitive and anatomical models of reading that have emerged from behavioral and lesion studies of dyslexia and functional neuroimaging studies of normal subjects. We then suggest that discrepancies in their findings can partly be overcome by functional neuroimaging studies of patients with acquired dyslexia. We present two such studies. One patient had a large left temporoparietal lesion which limited his reading to words with high semantic associations. When he read these words aloud, activation was observed in all areas of the normal reading system with the exception of the damaged left superior temporal lobe. The second patient had anterior temporal lobe atrophy with semantic dementia and a deficit in reading words that rely on lexical or semantic mediation. When asked to read aloud words on which she was likely to succeed, she activated all the normal areas, with increased activation in a left sensorimotor area associated with phonological processing and decreased activation in several areas associated with semantic processing. By relating these findings to those from lesion studies and imaging studies of normals, we propose that the translation of orthography to phonology is mediated semantically by the anterior part of the left midfusiform gyrus. In contrast, when semantic processing is compromised, the translation of orthography to phonology will be more reliant on the posterior part of the left midfusiform and the left frontal areas associated with phonology. Future studies are required to examine the connectivity between these areas during normal and abnormal reading.

Brain↗
PubMed2004

Mapping human brain function with MEG and EEG: methods and validation.

We survey the field of magnetoencephalography (MEG) and electroencephalography (EEG) source estimation. These modalities offer the potential for functional brain mapping with temporal resolution in the millisecond range. However, the limited number of spatial measurements and the ill-posedness of the inverse problem present significant limits to our ability to produce accurate spatial maps from these data without imposing major restrictions on the form of the inverse solution. Here we describe approaches to solving the forward problem of computing the mapping from putative inverse solutions into the data space. We then describe the inverse problem in terms of low dimensional solutions, based on the equivalent current dipole (ECD), and high dimensional solutions, in which images of neural activation are constrained to the cerebral cortex. We also address the issue of objective assessment of the relative performance of inverse procedures by the free-response receiver operating characteristic (FROC) curve. We conclude with a discussion of methods for assessing statistical significance of experimental results through use of the bootstrap for determining confidence regions in dipole-fitting methods, and random field (RF) and permutation methods for detecting significant activation in cortically constrained imaging studies.

Brain Mapping↗
PubMed2004

Computational anatomy: shape, growth, and atrophy comparison via diffeomorphisms.

Computational anatomy (CA) is the mathematical study of anatomy I in I = I(alpha) o G, an orbit under groups of diffeomorphisms (i.e., smooth invertible mappings) g in G of anatomical exemplars I(alpha) in I. The observable images are the output of medical imaging devices. There are three components that CA examines: (i) constructions of the anatomical submanifolds, (ii) comparison of the anatomical manifolds via estimation of the underlying diffeomorphisms g in G defining the shape or geometry of the anatomical manifolds, and (iii) generation of probability laws of anatomical variation P(.) on the images I for inference and disease testing within anatomical models. This paper reviews recent advances in these three areas applied to shape, growth, and atrophy.

Algorithms↗
PubMed2004

Statistics on diffeomorphisms via tangent space representations.

In this paper, we present a linear setting for statistical analysis of shape and an optimization approach based on a recent derivation of a conservation of momentum law for the geodesics of diffeomorphic flow. Once a template is fixed, the space of initial momentum becomes an appropriate space for studying shape via geodesic flow since the flow at any point along the geodesic is completely determined by the momentum at the origin through geodesic shooting equations. The space of initial momentum provides a linear representation of the nonlinear diffeomorphic shape space in which linear statistical analysis can be applied. Specializing to the landmark matching problem of Computational Anatomy, we derive an algorithm for solving the variational problem with respect to the initial momentum and demonstrate principal component analysis (PCA) in this setting with three-dimensional face and hippocampus databases.

Algorithms↗
PubMed2005

Program for Assisted Labeling of Sulcal Regions (PALS): description and reliability.

With the improvements in techniques for generating surface models from magnetic resonance (MR) images, it has recently become feasible to study the morphological characteristics of the human brain cortex in vivo. Studies of the entire surface are important for measuring global features, but analysis of specific cortical regions of interest provides a more detailed understanding of structure. We have previously developed a method for automatically segmenting regions of interest from the cortical surface using a watershed transform. Each segmented region corresponds to a cortical sulcus and is thus termed a "sulcal region." In this work, we describe two important augmentations of this methodology. First, we describe a user interface that allows for the efficient labeling of the segmented sulcal regions called the Program for Assisted Labeling of Sulcal Regions (PALS). An additional augmentation allows for even finer divisions on the cortex with a methodology that employs the fast marching technique to track a curve on the cortical surface that is then used to separate segmented regions. After regions of interest have been identified, we compute both the cortical surface area and gray matter volume. Reliability experiments are performed to assess both the long-term stability and short-term repeatability of the proposed techniques. These experiments indicate the proposed methodology gives both highly stable and repeatable results.

Algorithms↗
PubMed2005

Recipes for the linear analysis of EEG.

In this paper, we describe a simple set of "recipes" for the analysis of high spatial density EEG. We focus on a linear integration of multiple channels for extracting individual components without making any spatial or anatomical modeling assumptions, instead requiring particular statistical properties such as maximum difference, maximum power, or statistical independence. We demonstrate how corresponding algorithms, for example, linear discriminant analysis, principal component analysis and independent component analysis, can be used to remove eye-motion artifacts, extract strong evoked responses, and decompose temporally overlapping components. The general approach is shown to be consistent with the underlying physics of EEG, which specifies a linear mixing model of the underlying neural and non-neural current sources.

Algorithms↗
PubMed2006

A cortical potential imaging study from simultaneous extra- and intracranial electrical recordings by means of the finite element method.

In the present study, we have validated the cortical potential imaging (CPI) technique for estimating cortical potentials from scalp EEG using simultaneously recorded electrocorticogram (ECoG) in the presence of strong local inhomogeneity, i.e., Silastic ECoG grid(s). The finite element method (FEM) was used to model the realistic postoperative head volume conductor, which includes the scalp, skull, cerebrospinal fluid (CSF) and brain, as well as the Silastic ECoG grid(s) implanted during the surgical evaluation in epilepsy patients, from the co-registered magnetic resonance (MR) and computer tomography (CT) images. A series of computer simulations were conducted to evaluate the present FEM-based CPI technique and to assess the effect of the Silastic ECoG grid on the scalp EEG forward solutions. The present simulation results show that the Silastic ECoG grid has substantial influence on the scalp potential forward solution due to the distortion of current pathways in the presence of the extremely low conductive materials. On the other hand, its influence on the estimated cortical potential distribution is much less than that on the scalp potential distribution. With appropriate numerical modeling and inverse estimation techniques, we have demonstrated the feasibility of estimating the cortical potentials from the scalp EEG with the implanted Silastic ECoG gird(s), in both computer simulations and in human experimentation. In an epilepsy patient undergoing surgical evaluation, the cortical potentials were reconstructed from the simultaneously recorded scalp EEG, in which main features of spatial patterns during interictal spike were preserved and over 0.75 correlation coefficient value was obtained between the recorded and estimated cortical potentials. The FEM-based CPI technique provides a means of connecting the simultaneous recorded ECoG and the scalp EEG and promises to become an effective tool to evaluate and validate CPI techniques using clinic data.

Algorithms↗
PubMed2006

A new improved version of the realistic digital brain phantom.

Image analysis methods must be tested and evaluated within a controlled environment. Simulations can be an extremely helpful tool for validation because ground truth is known. We created the digital brain phantom that is at the heart of our publicly available database of realistic simulated magnetic resonance image (MRI) volumes known as BrainWeb. Even though the digital phantom had l mm(3) isotropic voxel size and a small number of tissue classes, the BrainWeb database has been used in more than one hundred peer-reviewed publications validating different image processing methods. In this paper, we describe the next step in the natural evolution of BrainWeb: the creation of digital brain phantom II that includes three major improvements over the original phantom. First, the realism of the phantom, and the resulting simulations, was improved by modeling more tissue classes to include blood vessels, bone marrow and dura mater classes. In addition. a more realistic skull class was created. The latter is particularly useful for SPECT, PET and CT simulations for which bone attenuation has an important effect. Second, the phantom was improved by an eight-fold reduction in voxel volume to 0.125 mm(3). Third, the method used to create the new phantom was modified not only to take into account the segmentation of these new structures, but also to take advantage of many more automated procedures now available. The overall process has reduced subjectivity and manual intervention when compared to the original phantom, and the process may be easily applied to create phantoms from other subjects. MRI simulations are shown to illustrate the difference between the previous and the new improved digital brain phantom II. Example PET and SPECT simulations are also presented.

Brain↗
PubMed2006

Thalamo-cortical connectivity in children born preterm mapped using probabilistic magnetic resonance tractography.

Our aim was to investigate the feasibility of studying white matter tracts and connections between the thalamus and the cortex in 2-year-old infants who were born preterm by probabilistic magnetic resonance (MR) tractography. Using this approach, we were able to visualize and quantify connectivity distributions in a number of white matter tracts, including the corticospinal tracts, optic radiations, fibers of the genu and splenium of the corpus callosum, superior longitudinal fasciculus and inferior fronto-occipital fasciculus, and to map the distribution within thalamus of fibers connecting to specific cortical regions. In eleven infants with no MR evidence of focal cerebral lesions and appropriate neurodevelopment as shown by general quotient (GQ) scores above 100, we mapped cortical connections to the thalamus that appeared similar to those reported in adults. However, in a proof-of-principle experiment, we examined one further child with marked white matter abnormalities and found that the volume and pattern of thalamo-cortical connections were severely disrupted. This technique promises to be a useful tool for assessing connectivity in the developing brain and in infants with lesions.

Cerebral Cortex↗
PubMed2006

Cell type-specific structural plasticity of axonal branches and boutons in the adult neocortex.

We imaged axons in layer (L) 1 of the mouse barrel cortex in vivo. Axons from thalamus and L2/3/5, or L6 pyramidal cells were identified based on their distinct morphologies. Their branching patterns and sizes were stable over times of months. However, axonal branches and boutons displayed cell type-specific rearrangements. Structural plasticity in thalamocortical afferents was mostly due to elongation and retraction of branches (range, 1-150 microm over 4 days; approximately 5% of total axonal length), while the majority of boutons persisted for up to 9 months (persistence over 1 month approximately 85%). In contrast, L6 axon terminaux boutons were highly plastic (persistence over 1 month approximately 40 %), and other intracortical axon boutons showed intermediate levels of plasticity. Retrospective electron microscopy revealed that new boutons make synapses. Our data suggest that structural plasticity of axonal branches and boutons contributes to the remodeling of specific functional circuits.

Analysis of Variance↗
PubMed2004

Embryogenesis of the peripheral nervous system.

Embryogenesis is a complex, wide-ranging event. Key processes may proceed simultaneously in different portions of the embryo, or sequentially, with phase offsets as waves of maturation pass outward from an initial point toward the periphery. The molecular signals used to pattern the body commonly serve multiple functions and reiterate as the body plan progresses. This article therefore presents first the anatomic model of the peripheral nervous system, so that the final goal is clear. It then reviews the terminology needed to describe embryogenesis. The article's first section reviews neural development. The main portion of the article addresses the maturation of the fetal nervous system in terms of the evolving gross morphology and the molecular signals that pattern these changes.

Embryonic and Fetal Development↗