Cortical potential imaging using L-curve and GCV method to choose the regularisation parameter

Background

The electroencephalography (EEG) is an attractive and a simple technique to measure the brain activity. It is attractive due its excellent temporal resolution and simple due to its non-invasiveness and sensor design. However, the spatial resolution of EEG is reduced due to the low conducting skull. In this paper, we compute the potential distribution over the closed surface covering the brain (cortex) from the EEG scalp potential. We compare two methods – L-curve and generalised cross validation (GCV) used to obtain the regularisation parameter and also investigate the feasibility in applying such techniques to N170 component of the visually evoked potential (VEP) data.

Methods

Using the image data set of the visible human man (VHM), a finite difference method (FDM) model of the head was constructed. The EEG dataset (256-channel) used was the N170 component of the VEP. A forward transfer matrix relating the cortical potential to the scalp potential was obtained. Using Tikhonov regularisation, the potential distribution over the cortex was obtained.

Results

The cortical potential distribution for three subjects was solved using both L-curve and GCV method. A total of 18 cortical potential distributions were obtained (3 subjects with three stimuli each – fearful face, neutral face, control objects).

Conclusions

The GCV method is a more robust method compared to L-curve to find the optimal regularisation parameter. Cortical potential imaging is a reliable method to obtain the potential distribution over cortex for VEP data.

     

Callosities,corns, and calluses.

Inappropriate shoes, abnormal foot mechanics, and high levels of activity produce pressure and friction that lead to corns and calluses. Most lesions can be managed conservatively by proper footwear, orthoses, and, if necessary, regular paring. The lesions usually disappear when the causative mechanical forces are removed. Surgery is rarely indicated and should be specifically aimed at correcting the abnormal mechanical stresses.     

Leptin administration improves skeletal muscle insulin responsiveness in diet-induced insulin-resistant rats

In addition to suppressing appetite, leptin may also modulate insulin secretion and action. Leptin was administered here to insulin-resistant rats to determine its effects on secretagogue-stimulated insulin release, whole body glucose disposal, and insulin-stimulated skeletal muscle glucose uptake and transport. Male Wistar rats were fed either a normal (Con) or a high-fat (HF) diet for 3 or 6 mo. HF rats were then treated with either vehicle (HF), leptin (HF-Lep, 10 mg. kg(-1). day(-1) sc), or food restriction (HF-FR) for 12-15 days. Glucose tolerance and skeletal muscle glucose uptake and transport were significantly impaired in HF compared with Con. Whole body glucose tolerance and rates of insulin-stimulated skeletal muscle glucose uptake and transport in HF-Lep were similar to those of Con and greater than those of HF and HF-FR. The insulin secretory response to either glucose or tolbutamide (a pancreatic beta-cell secretagogue) was not significantly diminished in HF-Lep. Total and plasma membrane skeletal muscle GLUT-4 protein concentrations were similar in Con and HF-Lep and greater than those in HF and HF-FR. The findings suggest that chronic leptin administration reversed a high-fat diet-induced insulin-resistant state, without compromising insulin secretion.     

Effect of oxygen on cyclic GMP-dependent protein kinase-mediated relaxation in ovine fetal pulmonary arteries and veins

Cyclic GMP-dependent protein kinase (PKG) plays an important role in regulating pulmonary vasomotor tone in the perinatal period. In this study, we tested the hypothesis that a change in oxygen tension affects PKG-mediated pulmonary vasodilation. Isolated intrapulmonary arteries and veins of near-term fetal lambs were first incubated for 4 h under hypoxic and normoxic conditions (Po2 of 30 and 140 mmHg, respectively) and then contracted with endothelin-1. 8-Bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP), a cell membrane-permeable analog of cGMP, induced a greater relaxation in vessels incubated in normoxia than in hypoxia. beta-Phenyl-1,N2-etheno-8-bromoguanosine-3',5'-cyclic monophosphorothioate, Rp isomer (Rp-8-Br-PET-cGMPS), a selective inhibitor of PKG, attenuated relaxation induced by 8-BrcGMP (10-4 and 3 x 10-4 M). In the presence of Rp-8-Br-PET-cGMPS, the differential responses to 8-BrcGMP between hypoxia and normoxia treatment were abolished in veins but not in arteries. cGMP-stimulated PKG activity was present in arteries but not in veins after 4 h of hypoxia. Both vessel types showed significant increase in cGMP-stimulated PKG activity after 4 h of normoxia. PKG protein (Western blot analysis) and PKG mRNA levels (quantitative RT-PCR) were greater in veins but not in arteries after 4-h exposure to normoxia vs. hypoxia. These results demonstrate that oxygen augments cGMP-mediated vasodilation of fetal pulmonary arteries and veins. Furthermore, the effect of oxygen on response of the veins to cGMP is due to an increase in the activity, protein level, and mRNA of PKG.     

Measurement of aortic input impedance in mice: effects of age on aortic stiffness

Mice are used with increasing frequency as models of human cardiovascular diseases, but significant gaps exist in our knowledge of vascular function in the aging mouse. We determined aortic input impedance spectra, pulse wave velocity, and augmentation index in adult (8-mo-old) and old (29-mo-old) mice to determine whether arterial stiffening occurred with age in mice as it does in humans. Pressure and blood velocity signals measured simultaneously from the same location in the ascending aorta were used to determine input impedance spectra (0-10 harmonics). The first minimum of the impedance modulus occurred at the second harmonic in adult mice but shifted to the fourth harmonic in old mice. Characteristic impedance (average of 2nd-10th harmonic) was 57% higher in old mice: 471 +/- 62 vs. 299 +/- 10 (SE) dyn.s.cm-3 (P < 0.05). Pulse pressure and augmentation index, determined from the aortic pressure signals, were also higher in old mice: 42 +/- 2.2 vs. 29 +/- 4.9 mmHg (P < 0.05) and 37 +/- 5 vs. 14 +/- 2% (P < 0.005). Aortic pulse wave velocity measured from the timing of upstrokes of the Doppler velocity signals was 45% higher in old mice: 416 +/- 22 vs. 286 +/- 14 cm/s (n = 3, P < 0.01). These results reproduce age-related findings reported in humans and confirm that mice may be used as models of age-related vascular stiffening.     

Analysis of host response to bacterial infection using error model based gene expression microarray experiments

A key step in the analysis of microarray data is the selection of genes that are differentially expressed. Ideally, such experiments should be properly replicated in order to infer both technical and biological variability, and the data should be subjected to rigorous hypothesis tests to identify the differentially expressed genes. However, in microarray experiments involving the analysis of very large numbers of biological samples, replication is not always practical. Therefore, there is a need for a method to select differentially expressed genes in a rational way from insufficiently replicated data. In this paper, we describe a simple method that uses bootstrapping to generate an error model from a replicated pilot study that can be used to identify differentially expressed genes in subsequent large-scale studies on the same platform, but in which there may be no replicated arrays. The method builds a stratified error model that includes array-to-array variability, feature-to-feature variability and the dependence of error on signal intensity. We apply this model to the characterization of the host response in a model of bacterial infection of human intestinal epithelial cells. We demonstrate the effectiveness of error model based microarray experiments and propose this as a general strategy for a microarray-based screening of large collections of biological samples.     

Stem flow and porometer measurements of transpiration from honey mesquite (Prosopis glandulosa)

The objective of this study was to compare stem flow and porometermethods of measuring transpiration of honey mesquite (Prosopisglandulosa) trees on a semiarid site. Stem flow was measuredusing heat balance stem flow gauges. Porometer measurementsof leaf stomatal conductance (g_s) were made within foliage layersof each stem and scaled to transpiration values for the entirestem (E_stem) using stem leaf area. Simultaneous measurementsusing both methods were made diurnally and under artificiallyimposed stem shading or defoliation in June and October 1990.Stem flow and E_stem had similar diumal patterns except on 2d in June when E_stem increased during the afternoon while stemflow declined relative to midday values. During October, E_stemwas greater than stem flow throughout the day. This was attributedto sampling error in which only undamaged leaves were used forporometer measurements yet, by this time in the growing season,many leaves on each stem were damaged from insects or wind andlikely had lower transpiration rates. A regression coefficientbetween E_stem and stem flow of 0.79 in June and 0.91 in Octobersuggested the two methods were comparable, but there was considerablevariation between methods during peak transpiration rates. Bothtechniques detected that artificial shading or defoliation causedsimilar relative declines in transpiration. Results imply thatestimates of stem transpiration can be obtained by scaling porometermeasurements of leaves but accuracy declines at higher transpirationrates. Key words: Sap flow, evapotranspiration, stomatal conductance, scaling, water relations     

An essential role of caffeoyl shikimate esterase in monolignol biosynthesis in Medicago truncatula

Biochemical and genetic analyses have previously identified caffeoyl shikimate esterase (CSE) as an enzyme in the monolignol biosynthesis pathway in Arabidopsis thaliana, although the generality of this finding has been questioned. Here we show the presence of CSE genes and associated enzyme activity in barrel medic (Medicago truncatula, dicot, Leguminosae), poplar (Populus deltoides, dicot, Salicaceae), and switchgrass (Panicum virgatum, monocot, Poaceae). Loss of function of CSE in transposon insertion lines of M. truncatula results in severe dwarfing, altered development, reduction in lignin content, and preferential accumulation of hydroxyphenyl units in lignin, indicating that the CSE enzyme is critical for normal lignification in this species. However, the model grass Brachypodium distachyon and corn (Zea mays) do not possess orthologs of the currently characterized CSE genes, and crude protein extracts from stems of these species exhibit only a weak esterase activity with caffeoyl shikimate. Our results suggest that the reaction catalyzed by CSE may not be essential for lignification in all plant species.     

Patients treated for amebic liver abscess develop cell-mediated immune responses effective in vitro against Entamoeba histolytica

We studied the afferent and efferent cell-mediated immune response in 15 patients treated for amebic liver abscess. Patients had a lower T4 to T8 ratio (1.25 +/- 0.65) compared with age- and sex-matched controls (1.89 +/- 0.44, p less than 0.01) due to a decrease in T4-"helper" cells and an increase in T8-"suppressor" cells (p less than 0.01). The in vitro proliferative response of patient T lymphocytes to the plant mitogen concanavalin A (Con A) was depressed; responses to phytohemagglutinin were not. The proliferative response of patient lymphocytes to an amebic soluble protein preparation (SPP) was greater than the mitogenic response seen in control lymphocytes (mean of 68,300 delta cpm and 22,300 delta cpm, respectively, p less than 0.001), correlated with the T4 to T8 ratio (p less than 0.05) and the duration of time from initiation of antiamebic therapy (p less than 0.01). Supernatants from patient lymphocytes exposed to the amebic SPP activated normal monocyte-derived macrophages to kill virulent axenic E. histolytica trophozoites (p less than 0.001); patient monocyte-derived macrophages activated by Con A-elicited lymphokine could also kill amebae. Finally, when incubated with the amebic SPP for 5 days, T lymphocytes from patients were able to kill virulent amebae (p less than 0.005); patient T lymphocytes not exposed to the amebic SPP or control T lymphocytes incubated for 5 days with the amebic SPP were not cytotoxic to E. histolytica trophozoites. In summary, after cure of amebic liver abscess, specific cell-mediated immune mechanisms develop that are effective in vitro against the parasite.