Selecting features for BCI control based on a covert spatial attention paradigm

Covert attention to spatial locations in the visual field is a relatively new control signal for brain–computer interfaces. Previous EEG research has shown that trials can be classified by thresholding based on left and right hemisphere alpha power in covert spatial attention paradigms. We reexamine the covert attention paradigm based on MEG measurements for fifteen subjects. It is shown that classification performance can be improved by applying sparse logistic regression in order to select a subset of the sensors specific to each subject as the basis for classification. Furthermore, insight is gained into how classification performance changes as a function of the length of the attention period and as a function of the number of trials. Classification performance steadily increases as the length of the attention period over which is averaged is increased, although this does not necessarily translate into higher bit rates. Good classification performance using early components of the attention period may be related to evoked response. With regard to the number of used trials, classification performance became maximal after 150 samples had been obtained, requiring a training time of approximately eleven minutes under the current experimental paradigm.     

Passive expiratory flow-volume curve is not an accurate method to measure the respiratory time constant in rabbits

BACKGROUND: In mechanically ventilated patients, inspiration is forced by an externally applied positive pressure whereas expiration remains passive and depends on the time constant of the total respiratory system (tau), which constitutes an important determinant of mechanical ventilation. The end-inspiratory occlusion technique is one of the easiest methods to obtain tau values in ventilated patients, especially infants, but its accuracy is not well established. The aim of this study was to compare in anesthetized, paralyzed rabbits tau values given by the end-inspiratory occlusion technique (tau(rs)) to tau values obtained by references methods for measurements (i.e. the product of static lung compliance by airway resistance: tau(ref)) during carbachol-induced bronchospasm eliciting marked modifications of the respiratory mechanics. METHODS: Comparisons were made in the basal state and after carbachol-induced bronchoconstriction in seven New Zealand adult rabbits. This procedure resulted in a wide range of expiratory time constants. A pneumotachograph was used to measure expiratory flow and volume before and after end-inspiratory occlusion. The slope of the flow volume curve gave tau(rs). Then tau(rs) was compared with tau(ref) (which ranged from 0.30 to 1.96 s). RESULTS: Statistical analysis revealed a weak correlation between the two methods, and a size-dependent bias of tau(rs) measurements. CONCLUSIONS: The end-inspiratory occlusion technique leads to a systemic bias in measurements of respiratory time constant, especially when the resistance of the respiratory system is elevated.     

Acid–base physiology: new concepts

The traditional approach to acid–base physiology is based on the Henderson–Hasselbalch equation which is derived from the ${\text{CO}}_2/{{\text{HCO}}_3}^{?}$ buffer system. However, it is becoming increasingly recognized that this is an incomplete analysis as it focuses on only one of the six reactions involving H⁺ and can lead to the incorrect assumption that CO₂ and ${{\text{HCO}}_3}^{?}$ are independently adjusted factors that ultimately determine pH. In 1983, Stewart, a Canadian physiologist, proposed that a fuller understanding of acid–base physiology required consideration of biological fluids as a complex dynamic system, taking into account the interactions of all the chemical species involved. He showed that the true independent variables controlling the pH of any given fluid compartment are: the difference in the concentration of ‘strong ions’; the total concentration of ‘weak acid’; and the PCO₂. Importantly, H⁺ and ${{\text{HCO}}_3}^{?}$ are dependent variables and it is incorrect to think of them as being specifically regulated to manipulate pH. This review will discuss the importance of pH homeostasis and highlight the implications of the Stewart approach in our understanding of acid–base control mechanisms and disorders. In particular, the true mechanisms by which the kidney regulates plasma pH will be discussed, emphasizing key misconceptions that have been propagated as a result of the traditional approach.     

Testing for rational bubbles in a coexplosive vector autoregression

Summary Asset bubbles can be described through the rational bubble solution of the standard stock price model linking stock prices and dividends. We show how the hypothesis of a rational bubble can be tested in the context of a bivariate coexplosive vector autoregression. The methodology is illustrated using US stock prices and dividends for the period 1974–2000.     

A benefit/risk approach towards selecting appropriate pharmaceutical dosage forms - An application for paediatric dosage form selection

The design and selection of new pharmaceutical dosage forms involves the careful consideration and balancing of a quality target product profile against technical challenges and development feasibility. Paediatric dosage forms present particular complexity due to the diverse patient population, patient compliance challenges and safety considerations of this vulnerable population. This paper presents a structured framework for assessing the comparative benefits and risks of different pharmaceutical design options against pre-determined criteria relating to (1) efficacy, (2) safety and (3) patient access. This benefit/risk framework has then been applied to three hypothetical, but realistic, scenarios for paediatric dosage forms in order to explore its utility in guiding dosage form design and formulation selection. The approach allows a rigorous, systematic and qualitative assessment of the merits and disadvantages of each dosage form option and helps identify mitigating strategies to modify risk. The application of a weighting and scoring system to the criteria depending on the specific case could further refine the analysis and aid decision-making. In this paper, one case study is scored for illustrative purposes. However, it is acknowledged that in real development scenarios, the generation of actual data considering the very specific situation for the patient/product/developer would come into play to drive decisions on the most appropriate dosage form strategy.     

Dural metastases from prostate cancer mimicking acute sub-dural hematoma

Metastases of prostate carcinoma to the central nervous system are rare, while dural metastases are even rarer. Patients are often clinically asymptomatic or present with non-specific symptoms, rendering the condition unsuspected. The imaging findings could resemble benign conditions and be misdiagnosed as such when the diagnosis is not considered. We present an unusual case of dural metastasis from carcinoma of the prostate mimicking acute sub-dural hematoma as shown on non-contrast-enhanced CT. The radiological features are analyzed, and clues to differentiating the two conditions are discussed.