Designing optimal stimuli to control neuronal spike timing

Recent advances in experimental stimulation methods have raised the following important computational question: how can we choose a stimulus that will drive a neuron to output a target spike train with optimal precision, given physiological constraints? Here we adopt an approach based on models that describe how a stimulating agent (such as an injected electrical current or a laser light interacting with caged neurotransmitters or photosensitive ion channels) affects the spiking activity of neurons. Based on these models, we solve the reverse problem of finding the best time-dependent modulation of the input, subject to hardware limitations as well as physiologically inspired safety measures, that causes the neuron to emit a spike train that with highest probability will be close to a target spike train. We adopt fast convex constrained optimization methods to solve this problem. Our methods can potentially be implemented in real time and may also be generalized to the case of many cells, suitable for neural prosthesis applications. With the use of biologically sensible parameters and constraints, our method finds stimulation patterns that generate very precise spike trains in simulated experiments. We also tested the intracellular current injection method on pyramidal cells in mouse cortical slices, quantifying the dependence of spiking reliability and timing precision on constraints imposed on the applied currents.     

Myxopapillary ependymoma of the conus medullaris presenting with intratumoral hemorrhage during weight lifting in a teenager

Intratumoral hemorrhage within a myxopapillary ependymoma of the conus medullaris and cauda equina is rare. Most patients with myxopapillary ependymoma present insidiously, but they may present with hemorrhage or cauda equina syndrome. Limited number of case reports available has described this condition only in adult patients. We report our experience with intratumoral hemorrhage of myxopapillary ependymoma of the conus medullaris during weight lifting in a 15-year-old boy.     

Caffeine reduces the initial dip in the visual BOLD response at 3 T

Localized changes in oxygen consumption related to increased neural activity can result in a small and transient "initial dip" of the blood oxygenation level-dependent (BOLD) signal used in functional magnetic resonance imaging (fMRI). The initial dip has been of great interest to the fMRI community because it may provide a more accurate and localized measure of neural activity than the conventional BOLD signal increase. Although potentially useful as a technique for human brain mapping, the initial dip is not always detected and has been a source of some controversy. In this study, the BOLD response to a 4-s long visual stimulus was measured with a 3-T MRI system in 5 healthy volunteers both before and immediately after a 200-mg oral caffeine dose. The caffeine dose significantly (P < 0.001) reduced or eliminated the initial dip in all subjects. These findings suggest that caffeine usage may be a key factor in the detection of the initial dip in human fMRI studies.     

The emerging role of cardiac computed tomography for the assessment of coronary perfusion: a systematic review and meta-analysis

Background

Computed tomography perfusion (CTP) is an emerging method which, coupled with the anatomical detail afforded by cardiac computed tomographic angiography (CCTA), may allow for determination of both structural and physiologic significance of coronary stenoses with a single imaging modality. This study was designed to execute a systematic review/meta-analysis to determine the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of CTP as compared with reference standards for detection of significant coronary artery stenoses and impaired perfusion.

Methods

A systematic review identified 13 out of 4368 studies allowing a calculation of sensitivity, specificity, PPV, and NPV on a per patient or per vessel or per segment basis using radionuclide myocardial perfusion imaging (MPI), conventional coronary angiography (CCA), magnetic resonance perfusion imaging (MRPI), or fractional flow reserve (FFR) as the reference standard. Meta-analyses of results were carried out using random effects modelling.

Results

Most studies used a maximal vasodilator stress protocol with adenosine, provided information mainly on a per vessel basis, and used myocardial perfusion imaging or CCA as the reference standard. Of the studies comparing combinations of both anatomical and functional imaging, the most rigourous standard was CCA/FFR. Compared with the latter, CCTA/CTP had sensitivity, specificity, PPV, and NPV of 81%, 93%, 87%, and 88%, respectively.

Conclusions

CTP shows promise as an adjunct to CCTA, potentially allowing determination of both structural and physiologic significance with a single imaging modality.     

Predisposing factors for renal scarring in children with urinary tract infection

This study was undertaken to determine the predisposing factors for renal scarring in children with urinary tract infection. In this prospective cohort study, 176 children with documented urinary tract infection were categorized into four groups: ≤1 year old, 1-2 years old, 2-7 years and 7-14 years old. Ultrasonography and Technetium-99 m-DMSA scan were used to detect the possible abnormalities. Infants under 12 months old presented as the most common group for renal scarring (27 cases, 52.9%), and vesicoureteral reflux (VUR) was diagnosed in 29 cases (56.8%). Fifteen (41.67%) children between the ages of one and two years had renal scar, and VUR was detected in half of the patients. In the third group, 36.3%, and in fourth group, 41.6% of the patients had renal scar. Also, 38.6% in group three and 50% in the final group had VUR. A co-incidental finding that was observed in this study was the high incidence of pseudohypoaldesteronism (PHA) in our patients: in 39.2% of the children in group one, 22.2% in group two and 4% in group three. In group four however, none of the patients had PHA. Risk of scar formation with urinary tract infection (UTI) was higher in the younger age group and in those with recurrent UTIs.