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PubMed2005

Localization bias and spatial resolution of adaptive and non-adaptive spatial filters for MEG source reconstruction.

This paper discusses the location bias and the spatial resolution in the reconstruction of a single dipole source by various spatial filtering techniques used for neuromagnetic imaging. We first analyze the location bias for several representative adaptive and non-adaptive spatial filters using their resolution kernels. This analysis theoretically validates previously reported empirical findings that standardized low-resolution electromagnetic tomography (sLORETA) has no location bias. We also find that the minimum-variance spatial filter does exhibit bias in the reconstructed location of a single source, but that this bias is eliminated by using the normalized lead field. We then focus on the comparison of sLORETA and the lead-field normalized minimum-variance spatial filter, and analyze the effect of noise on source location bias. We find that the signal-to-noise ratio (SNR) in the measurements determines whether the sLORETA reconstruction has source location bias, while the lead-field normalized minimum-variance spatial filter has no location bias even in the presence of noise. Finally, we compare the spatial resolution for sLORETA and the minimum-variance filter, and show that the minimum-variance filter attains much higher resolution than sLORETA does. The results of these analyses are validated by numerical experiments as well as by reconstructions based on two sets of evoked magnetic responses.

Algorithms↗
PubMed2004

Effects of gadolinium chloride on slowly adapting and rapidly adapting receptors of the rabbit lung.

Effects of gadolinium chloride, an inhibitor of stretch-activated channels, on the responses of slowly adapting receptors (SARs) and rapidly adapting receptors (RARs) to hyperinflation were investigated. The increase in activity of RARs resulting from sustained elevations of left atrial pressure (LAP) was also assessed with gadolinium chloride application. Action potentials (AP) of SARs and RARs during hyperinflation were recorded from the vagus nerve of anesthetized New Zealand White rabbits before and after application of gadolinium chloride (20mM) directly on the receptor area of the nerve endings. There was a significant reduction of activity in SARs (n = 9) and RARs (n = 7) after application of gadolinium chloride. Activity of RARs (n = 6) increased when the LAP was elevated by 5 and 10 mmHg. This effect was abolished after gadolinium chloride was applied to receptor endings and the activity was restored when gadolinium chloride was removed. This suggests that stretch-activated channels play a role in SARs and RARs activity.

Action Potentials↗
PubMed2001

Intrinsic versus extrinsic stabilization of enzymes: the interaction of solutes and temperature on A4-lactate dehydrogenase orthologs from warm-adapted and cold-adapted marine fishes.

We examined the effects of temperature and stabilizing solutes on A4-lactate dehydrogenase (A4-LDH) from warm- and cold-adapted fishes, to determine how extrinsic stabilizers affect orthologs with different intrinsic stabilities. Conformational changes during substrate binding are rate-limiting for A4-LDH, thus stabilization due to intrinsic or extrinsic factors leads to decreased activity. A4-LDH from a warm-temperate goby (Gillichthys mirabilis), which has lower values for kcat and the Michaelis constant for pyruvate ( K m PYR), was intrinsically more stable than the orthologs of the cold-adapted Antarctic notothenioids Parachaenichthys charcoti and Chionodraco rastrospinosus, as shown by a higher apparent transition ('melting') temperature (Tm(APP)). We used four solutes, glycerol, sucrose, trimethylamine-N-oxide and poly(ethylene glycol) 8000, which stabilize proteins through different modes of preferential exclusion, to study temperature-solute interactions of the three orthologs. Changes in Tm(APP) were similar for all orthologs in each solute tested, but the catalytic rate of G. mirabilis A4-LDH was decreased most by solutes and increased most by temperature. In contrast, the K m PYR values of the Antarctic orthologs were more affected than that of the goby by both solutes and temperature. We conclude that (a) preferential exclusion of solutes functions within the native state of A4-LDH to favor conformational microstates with minimal surface area; (b) the varied effects of the different solutes on the kinetic properties are due to the interaction between this nonspecific stabilization and the differing intrinsic stabilities of the orthologs; (c) the catalytic rates of A4-LDH orthologs are equally affected by stabilizing solutes, if measurements are made at physiologically appropriate temperatures; and (d) global stability and localized flexibility of these A4-LDH orthologs may evolve independently.

Animals↗
PubMed2002

ATP suppresses activity in slowly adapting but not rapidly adapting mechanoreceptors in toad skin.

To test the possible role of ATP in transducing or modulating touch sensation, an isolated skin-nerve preparation from the toad, Bufo marinus, perfused on the inner side, was used to examine the effects of ATP on slowly adapting (SA) and rapidly adapting (RA) mechanoreceptors, identified by ramp and hold indentation of the skin. ATP (1-50 mM) did not generate impulse activity in either SA or RA mechanoreceptors nor increase their responses to mechanical stimulation. Instead, ATP (> or =5 mM) reversibly and selectively suppressed impulse discharge from SA mechanoreceptors. Our results indicate that while ATP may modulate the responses of specific touch receptors, it is not involved in transducing touch into nerve impulses.

Action Potentials↗
PubMed2006

Nonlinear approximation based image recovery using adaptive sparse reconstructions and iterated denoising--Part II: Adaptive algorithms.

We combine the main ideas introduced in Part I with adaptive techniques to arrive at a powerful algorithm that estimates missing data in nonstationary signals. The proposed approach operates automatically based on a chosen linear transform that is expected to provide sparse decompositions over missing regions such that a portion of the transform coefficients over missing regions are zero or close to zero. Unlike prevalent algorithms, our method does not necessitate any complex preconditioning, segmentation, or edge detection steps, and it can be written as a progression of denoising operations. We show that constructing estimates based on nonlinear approximants is fundamentally a nonconvex problem and we propose a progressive algorithm that is designed to deal with this issue directly. The algorithm is applied to images through an extensive set of simulation examples, primarily on missing regions containing textures, edges, and other image features that are not readily handled by established estimation and recovery methods. We discuss the properties required of good transforms, and in conjunction, show the types of regions over which well-known transforms provide good predictors. We further discuss extensions of the algorithm where the utilized transforms are also chosen adaptively, where unpredictable signal components in the progressions are identified and not predicted, and where the prediction scenario is more general.

Algorithms↗
PubMed2004

Self-adaptive blind source separation based on activation functions adaptation.

Independent component analysis is to extract independent signals from their linear mixtures without assuming prior knowledge of their mixing coefficients. As we know, a number of factors are likely to affect separation results in practical applications, such as the number of active sources, the distribution of source signals, and noise. The purpose of this paper to develop a general framework of blind separation from a practical point of view with special emphasis on the activation function adaptation. First, we propose the exponential generative model for probability density functions. A method of constructing an exponential generative model from the activation functions is discussed. Then, a learning algorithm is derived to update the parameters in the exponential generative model. The learning algorithm for the activation function adaptation is consistent with the one for training the demixing model. Stability analysis of the learning algorithm for the activation function is also discussed. Both theoretical analysis and simulations show that the proposed approach is universally convergent regardless of the distributions of sources. Finally, computer simulations are given to demonstrate the effectiveness and validity of the approach.

Computer Simulation↗
PubMed1984

Modular distribution of neurons with slowly adapting and rapidly adapting responses in area 3b of somatosensory cortex in monkeys.

Recordings from the representations of the glabrous digits in area 3b of the somatosensory cortex of owl and macaque monkeys revealed two types of neurons. Rapidly adapting (RA) neurons responded only at the onset and offset of a 1-s skin indentation. Slowly adapting (SA) neurons also responded to stimulus onset and offset but, in addition, they responded throughout the 1-s skin indentation. RA neurons were found in all cortical layers while SA neurons were found only in the middle cortical layers. In electrode penetrations perpendicular to the layers, some penetrations encountered only RA neurons (RA penetrations), while other penetrations first encountered RA neurons, then SA neurons, and finally RA neurons again (SA penetrations). When closely spaced electrode penetrations were made throughout the representation of a single digit, it was apparent that RA and SA penetrations were not randomly distributed. The distribution suggested the existence of separate clusters or bands of SA and RA neurons in the middle layers of cortex. The predominant orientation of the SA and RA regions was rostrocaudally along the lengths of the digit representations. The SA and RA bands varied in width, had no systematic position in the representation of individual digits, and often crossed from the representation of one digit to another. Because of overlapping receptive fields for neurons in adjoining bands, the SA and RA bands appeared to represent the digits separately. This would allow all skin surfaces for each digit to be subserved by both types of neurons.

Animals↗
PubMed1996

Altered behaviour of hamsters by prolonged hypergravity: adaptation to 2.5 G and re-adaptation to 1 G.

We studied the functional adaptation process in 40 hamsters subjected to either prolonged hypergravity to normal gravity. Subadult golden hamsters (n = 20) exposed to a hypergravity condition of 2.5 G for 6 months were tested to investigate the effect of hyper gravity on the perceptive motor skills and compared with control hamsters (n = 20). The motor coordination of the hypergravity hamsters hardly changed; locomotion was normal and swimming was possible. Equilibrium maintenance was disturbed during the first 3 months as was shown by the higher crossing time (p < 0.001) and higher fall frequency (p < 0.001) for the hypergravity group. Significant differences were also found in orientation during swimming (p = 0.007) and turning behaviour in the rotation task (p < 0.001) and in the no-rotation task (p = 0.029). After 6 months, 10 hamsters of both groups were tested for another 4 months, also the hypergravity hamsters were living at 1 G. Differences in orientation in the two groups did not change during swimming and turning behaviour during the rotation task (p = 0.026). Based on our findings, we conclude that the hamsters functionally adapted to hypergravity, which led to an altered performance of several tasks. The condition continued after 4 months of normal gravity.

Animals↗
PubMed1994

Effects of trifluoperazine and amiloride on the extrusion of axoplasmic Ca++ by rapidly adapting and slowly adapting type I cutaneous mechanoreceptors: an electron-microscopic study using the oxalate-antimonate method.

Influences of Ca++ transport inhibitors on the extrusion of cytosolic Ca++ from axon terminals of oral mucosal mechanoreceptors were cytochemically studied through the use of trifluoperazine (TFP), a Ca++ pump inhibitor, and amiloride, a Na+/Ca++ exchanger inhibitor. Palates of Mongolian gerbils were isolated after perfusion with normal, TFP-containing, or amiloride-containing HEPES-buffered saline, and then mechanically stimulated in the same buffer. Cytosolic Ca++ in axon terminals at 2 min after the stimulation was visualized by means of an oxalate-antimonate method using microwave fixation, and then evaluated electron-microscopically. TFP was found to inhibit the Ca++ extrusion from axon terminals of Meissner corpuscles, but not from those of Merkel cell-axon complexes. Conversely, amiloride severely reduced the Ca++ extrusion from axon terminals of Merkel cell-axon complexes, but not from those of Meissner corpuscles. These results suggest that cytosolic Ca++ extrusion from axon terminals of rapidly adapting and slowly adapting type I mechanoreceptors is regulated by a Ca++ pump and an Na+/Ca++ exchanger, respectively.

Amiloride↗
PubMedDate not supplied

Comparative evaluation of cell culture-adapted and chicken embryo-adapted fowl pox vaccine strains.

Two types of vaccines, chicken embryo adapted (VacCE) and cell culture adapted (VacCC), were tested for their efficacy to elicite the immune response in birds vaccinated at 2 and 8 wk of age. The cell-mediated immune response studied by blastogenesis assay showed that birds vaccinated at the second week of age by both VacCE and VacCC vaccines had significant increase in T-lymphocyte count at 21 days postvaccination (PV) and 7 days postchallenge (PC), whereas in birds vaccinated at 8 wk of age, a significant increase was seen at 21 days PV and 7 days PC with the VacCC vaccine. The rise in passive hemagglutination titers was observed up to 21 days PV and 7 days PC in birds vaccinated at 2 wk of age. However, only the birds vaccinated with VacCC at 8 wk of age showed rise in titers at days 21 PV and 7 PC. Birds were challenged 90 days PV by scarification on the thigh region, and the birds vaccinated with VacCC showed 90% and 70% protection when vaccinated at 2 and 8 wk, respectively. The birds vaccinated with VacCE showed only 60% and 20% protection at the corresponding levels, respectively.

Animals↗
PubMed1999

[In vitro comparison of marginal adaptation of different filling materials. II. Effect of the site and method of preparation on the marginal adaptation].

In a two-month in vitro experiment we examined the marginal adaptation of ten dental materials. Fifty Class II restorations were prepared extending to the cemento-enamel junction. The cavities of the composite restorations were bevelled at the vestibulo-occlusal and -approximal enamel margins, on the other side enamel and gingival margins were prepared conventionally. The specimens were thermocycled and examined with SEM. The microleakage was measured at the vestibulo-occlusal and -approximal tooth-filling junction, where adhesive technique was used, and at the gingival, oroocclusal and -approximal margins, which were not bevelled before. The obviously most important conclusion of the study is, that in the case of deep Class II cavities the amalgam has a better adaptation at the gingival margin than the examined composite resins.

Dental Amalgam↗
PubMed1999

Cross-cultural adaptation of a health status classification system in children with cancer. First results of the French adaptation of the Health Utilities Index Marks 2 and 3.

Our objective was to adapt and validate the Health Utilities Index Mark 2 (HUI 2) and HUI 3 health status classification systems self-report questionnaire in a population of children with cancer, a group of 42 children already included in a multi-centre database designed by the Group on Brain Tumors in Children of the French Society for Pediatric Oncology. Children were recruited during a routine consultation. Most of them had completed treatment. The version of the questionnaire for French adults was adapted linguistically for children. Open-ended queries by children about the comprehensiveness of the questions and very low non-response rates showed a good acceptability of the questionnaire. The main psychometric properties of the HUI 2 and HUI 3 classification systems were assessed in 3 groups of raters (child, parent, physician): construct validity was tested against the rating of the child's health state on a Likert scale and through comparison with clinical data, and internal consistency was determined through multi-trait analysis. Weighted and unweighted kappa values were used to measure the inter-rater agreement between the child's, parent's and physician's assessment of the child's health state. The convergent validity was satisfactory, with better results when the physician's assessment was used. The most affected attributes were the expected ones (i.e., cognition, pain and emotion). Disagreement was observed between the 3 raters, more often in the same direction: taking the child's assessment as the reference, the parents tended to under-estimate the health status while physicians tended to over-estimate it.

Adolescent↗
PubMed1990

[Adaptability of composite resin inlays. 1. Adaptability to the experimental MOD cavity prepared in an acrylic block].

The adaptability of composite resin inlays was examined. CR Inlay and INLAY/ONLAY were used as materials. After the CR Inlay was polymerized in a U-form metal mold, the dimensional changes were measured before and after heating. Furthermore, the composite resin inlays made according to the manufacturer's instructions were cemented in an MOD type cavity and the film thickness of the cement was measured. The polymerization shrinkage of CR Inlay was 0.63% in the inside of the inlay and after heating it increased to 0.71%. The film thickness of the cement in the case of CR Inlay was more than 250 microns and that in the case of the INLAY/ONLAY was more than 750 microns in the MOD type cavity. Dentacolor XS (a box type photo generator) was better than Wite Lite (a handy type photo generator) for the polymerization of CR Inlay. Because of the poor adaptation of the inlays and the difficulty in removing a inlay from a stone model for CR Inlay, perhaps polymerization shrinkage of the inlay should be compensated in some way.

Cementation↗
PubMed1990

[Automatic adaptation of stationary field dose distributions to the individual geometry of the patient. II: A model for adaptation of dose distributions].

Starting point for automatic adaptation of a dose distribution is a starting variant which parameters values are fixed as a matter of experience. On base of this starting variant a limited number of variants is produced and the "quality" of the attained dose distribution in each case is expressed by an added measure function value. A gradual improvement of adaptation of dose distribution to individual geometry of patients is done by pointed search of new parameter values for field breadths, field beginning points, field weights, and field insolation directions.

Humans↗
PubMed1985

[Effects of various anesthesia procedures used in forceps delivery on the cardiopulmonary adaptation of the newborn infant. 2. Modification of pulmonary adaptation].

Mature newborns reveal the same pulmonal adaption to extrauterine conditions after forceps delivery in general anesthesia for the mother beginning with propanidid or hexobarbital as newborns after spontaneous delivery. Intervalls of apnoe, being physiological during neonatal adaption up to the fourth life-hour, occurred in all three tested groups in the same frequency. Genuine apnoe in combination with following bradycardia and cyanosis couldn't be observed. Moreover during the whole examination time all mean values of respiration frequency were physiological. Therefore we believe that there is no fundamental deterioration of newborns respiration, i.e. a depression in nerve-centre, caused by propanidid or by hexobarbital, despite of repeatedly contrary description.

Anesthesia, Obstetrical↗
PubMed1976

[Altitude adaptation. Part II. Altitude adaptation as a problem of human biology. I. Growth)].

There are 3 main components influencing the mean stature of high altitude natives. The lower mean birthweight, which seems to result from the impossibility of complete adaptation during the last trimenon of gestation, which cannot be fully compensated during life. The general protein deficiency, or the habits of nutrition which are not comparable with the food-composition in industry-nations may be important. A definitive undernourishment has not been observed in those nations with longtime adaptation to the available food since generations, but several deficiencies of substances which specially influence growth, cannot be outruled. We also have to recognize the generally lower mean stature of the population in whole (South America Indians), that means of the both parents of a child. In the presence of low gene flow from one to the other generation this may influence also individual body measurement.

Acclimatization↗
PubMed1996

The central adaptation syndrome: psychosocial stress as a trigger for adaptive modifications of brain structure and brain function.

This review makes an attempt to combine data from biological and psychosocial stress literature and to suggest an alternative interpretation of the relationship between stress and disease. It rearranges the presently available knowledge on the short- and long-term effects of stress on many different aspects of brain structure and brain function in the form of a new conceptualization of the biological role of the stress response. The higher associative brain structures are not only the sites in which environmental and psychosocial demands are recognized and from which a less or more systemic, i.e. controllable or uncontrollable, stress response is initiated. They are also the sites which are primarily affected in the course of the stress response: the stress response acts as a trigger for the adaptive modification of the structure and the function of the brain of higher vertebrates and serves thus to adjust, in a self-optimizing manner, the behavior of an individual to the ever-changing requirements of its external world. This novel concept summarizes a large amount of information into a framework that lends itself to testable strategies for future research.

Adaptation, Physiological↗
PubMed1995

The immunogenicity of reassortants of the cold-adapted influenza A master strain A/Ann Arbor/6/60 is determined by both the genes for cold-adaptation and the haemagglutinin gene.

Two surface antigen segregants were prepared by co-infection of chicken embryo kidney cell cultures with reassortants of the cold-adapted influenza A master strain A/Ann Arbor/6/60-ca (H2N2) possessing the surface antigens of A/Queensland/6/72 (H3N2) and A/Hong Kong/123/77 (H1N1) and other genes that were common to the master strain. The segregants were shown by serological tests to possess H3N1 and H1N2 surface antigens but it was not possible to determine the presence of H1 or N1 genes by single-stranded RNA polyacrylamide gel electrophoresis. The immunogenic properties of A/Queensland/6/72-ca and H3N1 segregant CR6/35/2/9 were compared by immunising mice intranasally with graded doses of each virus twice at an interval of 3 weeks and then challenging with the wild-type A/Queensland/6/72 (H3N2). Clearance of the challenge virus occurred in mice immunised with the same vaccinating dose, indicating that the immunogenicity of both the ca H3N2 and H3N1 viruses was identical and similar findings were obtained for mice immunised with A/Hong Kong/123/77-ca and the H1N2 segregant CR6/35/1/19 and challenged with the wild-type A/Hong Kong/123/77. Therefore, there appears to be a good correlation between immunogenicity and the inheritance of the haemagglutinin gene.

Adaptation, Physiological↗