Gene expression variation in the brains of harvester ant foragers is associated with collective behavior.

Natural selection on collective behavior acts on variation among colonies in behavior that is associated with reproductive success. In the red harvester ant (Pogonomyrmex barbatus), variation among colonies in the collective regulation of foraging in response to humidity is associated with colony reproductive success. We used RNA-seq to examine gene expression in the brains of foragers in a natural setting. We find that colonies differ in the expression of neurophysiologically-relevant genes in forager brains, and a fraction of these gene expression differences are associated with two colony traits: sensitivity of foraging activity to humidity, and forager brain dopamine to serotonin ratio. Loci that were correlated with colony behavioral differences were enriched in neurotransmitter receptor signaling & metabolic functions, tended to be more central to coexpression networks, and are evolving under higher protein-coding sequence constraint. Natural selection may shape colony foraging behavior through variation in gene expression.

Hemiplegia and bilateral globus pallidus infarcts after carbon monoxide poisoning: case report.

The vast clinical manifestations of carbon monoxide (CO) poisoning can involve the neurological, neuropsychological and cardiac systems as well as others. In this case report, we describe our management of a 64-year-old woman exposed to CO in her apartment. Her presentation was unusual in that she had symmetric globus pallidus lesions, no evidence of thrombosis, but the lateralizing neurologic manifestation of severe hemiplegia.

Attitude Towards Alzheimer's Disease Among Undergraduate Students of University of the West Indies, Trinidad and Tobago.

BACKGROUND: Alzheimer's disease is most common among the dementias and is characterized by gradual declines in functional and cognitive abilities. Caregivers including family members play a key role in providing critically needed care for these patients. OBJECTIVE: This study compared the knowledge and attitudes of pre-healthcare and non-medical undergraduate students towards patients with Alzheimer's disease. MATERIALS AND METHODS: A cross-sectional study was conducted involving quota sampling of 691 undergraduate students (369 pre-healthcare and 322 non-medical). A 28-item questionnaire was utilised comprising of closed-ended questions and some based on a scale rating. The students' knowledge of Alzheimer's disease was arranged into categories such as: 0 for no knowledge about Alzheimer's disease, 1 for very little knowledge about Alzheimer's disease, 2 for fair knowledge about Alzheimer's disease and 3 for great knowledge about Alzheimer's disease. STATISTICAL ANALYSIS: The data was analysed using the computer software SPSS and the Chi squared test of independence was also used to determine which knowledge variables were independent of student's status. RESULTS: Overall, 40.01% of the students have great or fair knowledge of Alzheimer's disease, with that of pre-healthcare students being satisfactory (54.47%). Pre-healthcare students have a more positive attitude towards Alzheimer's disease and 82.2% of students wished to take advantage of predictive test for Alzheimer's disease. Age and genetics were identified as risk factors of the disease. CONCLUSION: Pre-healthcare students had greater understanding of Alzheimer's disease and depicted a more empathetic and caring attitude towards patients. This can be attributed mainly to their knowledge and exposure toward the disease.

A Survey of Primary Care Offices: Triage of Poisoning Calls without a Poison Control Center.

Poison control centers hold great potential for saving health care resources particularly by preventing unnecessary medical utilization. We developed a four-question survey with three poisoning-related scenarios, based on common calls to our poison center, and one question regarding after-hours calls. We identified primary care provider offices in our poison center's region from an internet search. We contacted these offices via telephone and asked to speak to an office manager or someone responsible for triaging patient phone queries. Using a scripted form, trained investigators questioned 100 consecutive primary care provider offices on how they would handle these poisoning-related calls if there was no poison center to refer their patients to. Results of our survey suggest that 82.5% of poisoning-related calls to primary care offices would be referred to 911 or an emergency department if there was no poison center. These results further support the role that poison centers play in patient care and health care utilization.

Effects of gastrointestinal tissue structure on computed dipole vectors.

BACKGROUND: Digestive diseases are difficult to assess without using invasive measurements. Non-invasive measurements of body surface electrical and magnetic activity resulting from underlying gastro-intestinal activity are not widely used, in large due to their difficulty in interpretation. Mathematical modelling of the underlying processes may help provide additional information. When modelling myoelectrical activity, it is common for the electrical field to be represented by equivalent dipole sources. The gastrointestinal system is comprised of alternating layers of smooth muscle (SM) cells and Interstitial Cells of Cajal (ICC). In addition the small intestine has regions of high curvature as the intestine bends back upon itself. To eventually use modelling diagnostically, we must improve our understanding of the effect that intestinal structure has on dipole vector behaviour. METHODS: Normal intestine electrical behaviour was simulated on simple geometries using a monodomain formulation. The myoelectrical fields were then represented by their dipole vectors and an examination on the effect of structure was undertaken. The 3D intestine model was compared to a more computationally efficient 1D representation to determine the differences on the resultant dipole vectors. In addition, the conductivity values and the thickness of the different muscle layers were varied in the 3D model and the effects on the dipole vectors were investigated. RESULTS: The dipole vector orientations were largely affected by the curvature and by a transmural gradient in the electrical wavefront caused by the different properties of the SM and ICC layers. This gradient caused the dipoles to be oriented at an angle to the principal direction of electrical propagation. This angle increased when the ratio of the longitudinal and circular muscle was increased or when the the conductivity along and across the layers was increased. The 1D model was able to represent the geometry of the small intestine and successfully captured the propagation of the slow wave down the length of the mesh, however, it was unable to represent transmural diffusion within each layer, meaning the equivalent dipole sources were missing a lateral component and a reduced magnitude when compared to the full 3D models. CONCLUSION: The structure of the intestinal wall affected the potential gradient through the wall and the orientation and magnitude of the dipole vector. We have seen that the models with a symmetrical wall structure and extreme anisotropic conductivities had similar characteristics in their dipole magnitudes and orientations to the 1D model. If efficient 1D models are used instead of 3D models, then both the differences in magnitude and orientation need to be accounted for.

Anatomically realistic multiscale models of normal and abnormal gastrointestinal electrical activity.

One of the major aims of the International Union of Physiological Sciences (IUPS) Physiome Project is to develop multiscale mathematical and computer models that can be used to help understand human health. We present here a small facet of this broad plan that applies to the gastrointestinal system. Specifically, we present an anatomically and physiologically based modelling framework that is capable of simulating normal and pathological electrical activity within the stomach and small intestine. The continuum models used within this framework have been created using anatomical information derived from common medical imaging modalities and data from the Visible Human Project. These models explicitly incorporate the various smooth muscle layers and networks of interstitial cells of Cajal (ICC) that are known to exist within the walls of the stomach and small bowel. Electrical activity within individual ICCs and smooth muscle cells is simulated using a previously published simplified representation of the cell level electrical activity. This simulated cell level activity is incorporated into a bidomain representation of the tissue, allowing electrical activity of the entire stomach or intestine to be simulated in the anatomically derived models. This electrical modelling framework successfully replicates many of the qualitative features of the slow wave activity within the stomach and intestine and has also been used to investigate activity associated with functional uncoupling of the stomach.

Modeling cardiac electrical activity at the cell and tissue levels.

Significant tissue structures exist in cardiac ventricular tissue, which are of supracellular dimension. It is hypothesized that these tissue structures contribute to the discontinuous spread of electrical activation, may contribute to arrhythmogenesis, and also provide a substrate for effective cardioversion. However, the influences of these mesoscale tissue structures in intact ventricular tissue are difficult to understand solely on the basis of experimental measurement. Current measurement technology is able to record at both the macroscale tissue level and the microscale cellular or subcellular level, but to date it has not been possible to obtain large volume, direct measurements at the mesoscales. To bridge this scale gap in experimental measurements, we use tissue-specific structure and mathematical modeling. Our models, which can incorporate ion channel models at the cell level into the reaction-diffusion equations at the tissue level, have enabled us to consider key hypotheses regarding discontinuous activation.

Solving the cardiac bidomain equations for discontinuous conductivities.

Fast simulations of cardiac electrical phenomena demand fast matrix solvers for both the elliptic and parabolic parts of the bidomain equations. It is well known that fast matrix solvers for the elliptic part must address multiple physical scales in order to show robust behavior. Recent research on finding the proper solution method for the bidomain equations has addressed this issue whereby multigrid preconditioned conjugate gradients has been used as a solver. In this paper, a more robust multigrid method, called Black Box Multigrid, is presented as an alternative to conventional geometric multigrid, and the effect of discontinuities on solver performance for the elliptic and parabolic part is investigated. Test problems with discontinuities arising from inserted plunge electrodes and naturally occurring myocardial discontinuities are considered. For these problems, we explore the advantages to using a more advanced multigrid method like Black Box Multigrid over conventional geometric multigrid. Results will indicate that for certain discontinuous bidomain problems Black Box Multigrid provides 60% faster simulations than using conventional geometric multigrid. Also, for the problems examined, it will be shown that a direct usage of conventional multigrid leads to faster simulations than an indirect usage of conventional multigrid as a preconditioner unless there are sharp discontinuities.

Cardiac electrophysiology and tissue structure: bridging the scale gap with a joint measurement and modelling paradigm.

Significant tissue structures exist in cardiac ventricular tissue that are of supracellular dimension. It is hypothesized that these tissue structures contribute to the discontinuous spread of electrical activation, may contribute to arrhymogenesis and also provide a substrate for effective cardioversion. However, the influences of these mesoscale tissue structures in intact ventricular tissue are difficult to understand solely on the basis of experimental measurement. Current measurement technology is able to record at both the macroscale tissue level and the microscale cellular or subcellular level, but to date it has not been possible to obtain large volume, direct measurements at the mesoscales. To bridge this scale gap in experimental measurements, we use tissue-specific structure and mathematical modelling. Our models have enabled us to consider key hypotheses regarding discontinuous activation. We also consider the future developments of our intact tissue experimental programme.

Multilevel homogenization applied to the cardiac bidomain equations.

Accurate cardiac tissue-based modeling using the bidomain equations requires the incorporation of fine-scale structures observed at the 50-100 micron level. By including such features we can more easily observe how defibrillation shocks lead to total depolarization of the heart. Several modeling studies that have investigated the effect of fine scale structures on defibrillation success have been completed. Results have shown that such structures aid, through the creation of virtual electrodes, in total depolarization. An obstacle that occurs with this modeling style is the massive amount of data that must be incorporated into detailed tissue models for even a cubic millimeter sample of cardiac tissue. In this paper, we discuss our approach to generating upscaled, or homogenized, versions of these models that can be used to perform simulations at a more reasonable modeling scale. They have the advantage of incorporating fine scale structure into the model at a reduced modeling cost. We introduce and briefly explore the advantages of this upscaling method.

A comparison of multilevel solvers for the cardiac bidomain equations.

Computing the extracellular potentials in a bidomain cardiac activation model is a computationally significant step in the solution process. Thus, using a fast solver can drastically reduce the overall time of simulation. Solving for the extracellular potentials involves inverting the matrix coming from the elliptic equation describing the extracellular-intracellular potential coupling. Elliptic equations are known to yield matrices that become progressively more ill-conditioned as the spatial resolution is increased. However, optimal multilevel solution methods are known to exist for these equations given enough effort is placed into developing the correct solution components. Two multilevel solvers that automatically perform much of this work are black box multigrid (BOXMG) and algebraic multigrid (AMG). In this paper, we compare the performance of BOXMG and AMG as solvers for the elliptic component of the bidomain equations. Our investigation is with respect to simulations of reentry in two-dimensional cardiac tissue.