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Results for “Model explainability”

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At least 685 records · Page 38Linked to original sources

PubMed2003

The association between age and depression in the general population: a multivariate examination.

OBJECTIVE: In a large general population study we found a close to linear rise with age in the mean score and prevalence of self-reported symptoms of depression. The aim of this study was to examine if this linear relation prevailed when controlled for multiple variables and to examine factors that eventually explained the association. METHOD: Among individuals aged 20-89 years living in Nord-Trøndelag County of Norway, 60 869 filled in valid ratings of the Hospital Anxiety and Depression Scale as well as many other variables. Covariates were grouped into a multivariate model with six blocks. Logistic regression was used to model the blocks and variables with caseness of depression as the dependent variable. RESULTS: The model explains a considerable part of the age-related pattern on depression. The pattern became less distinct in the age groups above 50 years. Variables within the blocks of somatic diagnoses and symptoms, as well as impairment, had most explanatory power. CONCLUSION: Because of our large sample we were able to control for more relevant variables than earlier studies. In contrast to most other studies, we found that an age-related increase of the prevalence of depression persisted after control for multiple variables.

Adult↗

PubMed1979

Monoamine oxidase inhibition by beta-carbolines: a quantum chemical approach.

Monoamine oxidase inhibition by beta-carboline derivatives is related to the energy change, delta E, arising from complex formation between the inhibitor and the enzyme. The energy change was expressed in terms of electronic indexes, which were estimated for a set of aromatic beta-carbolines. The electronic indexes were correlated to the experimental activity indexes by a simplified quantum chemical perturbational treatment with a multiple regression procedure. A characteristic structure for the inhibitor-enzyme complex was derived from the correlation. The molecules are linked by two kinds of bond. One involves the lone pyridine nitrogen pair of beta-carbolines; the other is due to a pi-electronic interaction between the inhibitor indole fragment and a suitable area of the enzyme. Such a model explains the competitive inhibition by beta-carbolines compared to tryptamine and other aromatic amines that are monoamine oxidase substrates.

Carbolines↗

PubMedDate not supplied

Genetics of human body size and shape: evidence for an oligogenic control of adiposity.

In a previous study by the authors in each of the pedigree samples from Kirghizstan, Turkmenia and Chuvashia, four principal factors supposedly controlled by four non-overlapping gene subsets were found. About 90% of total variation of adiposity as assessed by 22 measurements of skinfolds, circumferences and indices were covered by these factors. This study provides results of segregation analysis of each of these four factors. By the usual transmission probability tests, major gene (MG) control was accepted in all 12 analyses--four traits in three populations. Some of the most parsimonious MG models included non-MG effects, such as correlation of residuals between spouses, between parent and offspring and between sibs. The Kirghizian samples showed a significant assortative mating effect as measured by the correlation between genotypic values at putative MG in spouses. The proportion of the trait variance attributable to the MG effect varied from 0.296 (factor F4 in the Chuvashia sample) to 0.596 (the same factor in the Kirghizian sample). It is assumed that four independent large-effect genes can be recognized in the genetic control of adiposity determining, respectively, individual predisposition to accumulate subcutaneous fat, its distribution between the body trunk and extremities, predisposition to accumulate inner fat and its distribution between the upper and lower body parts. In each population, unification of the four most parsimonious MG models forms oligogenic models explaining from 0.364 (Chuvashia) to 0.540 (Kirghizstan) of total adiposity.

Adipose Tissue↗

PubMed2002

Is "somatic" angiotensin I-converting enzyme a mechanosensor?

"Somatic" angiotensin I-converting enzyme (ACE) appears to be one of the evolutionary advances that made a closed circulation possible, and may have contributed to the Cambrian "explosion" of species approximately 540 million years ago. It also appears to be at the origin of a large number of common human diseases. A model is proposed in which the duplicated form of ACE ("somatic" ACE) functions as a mechanotransducer, defending downstream vessels and tissues from an increase in pressure. In the model, ACE senses shear stress (blood velocity) in regions of turbulent blood flow. An increase in shear stress strips an autoinhibitor tripeptide, FQP, from the N-terminal active site, thereby activating it. The C-terminal domain is constitutively activated by chloride. This model explains the clinical superiority of hydrophobic ACE inhibitors relative to hydrophilic ones.

Animals↗

PubMed2003

Satisfaction with mental health services among people with schizophrenia in five European sites: results from the EPSILON Study.

Patient satisfaction with services is an important outcome variable that is increasingly used in mental health service evaluation. This study includes 404 people with schizophrenia in five European sites and addresses five questions focused on site, service, and patient characteristics as variables that might explain service satisfaction, using the Verona Service Satisfaction Scale. Patient satisfaction differed significantly across sites (highest in Copenhagen, lowest in London). In all sites, patients were least satisfied with involvement of relatives in care and information about illness. A multiple regression model showed that lower levels of total service satisfaction were associated with living in London or Santander, being retired/unemployed, having more hospital admissions, having more severe psychopathology, having more unmet needs, or having lower satisfaction with life. This model explained 31 percent of variance in service satisfaction. Our data show that service satisfaction can be seen as a result of (1) the ability of the service to provide a standard of care above a certain quality threshold, and (2) the perception of each patient that the care received has been tailored to the patient's own problems.

Adult↗

PubMed1994

Modelling contrast sensitivity as a function of retinal illuminance and grating area.

We extended the contrast detection model of human vision [Rovamo, Luntinen & Näsänen (1993b) Vision Research, 33, 2773-2788] to low light levels by taking into account the effect of light-dependent quantal noise. The extended model comprises (i) low-pass filtering due to the optical modulation transfer function of the eye, (ii) addition of light-dependent noise at the event of quantal absorption, (iii) high-pass filtering of neural origin (lateral inhibition), (iv) addition of internal neural noise, and (v) detection by a local matched filter whose efficiency decreases with increasing grating area. To test the model we measured foveal contrast sensitivity as a function of retinal illuminance and grating area at spatial frequencies of 0.125-32 c/deg. In agreement with the model, monocular contrast sensitivity at all grating areas increased in proportion to I when retinal illuminance (I) was smaller than critical illuminance. Thereafter the increase saturated and contrast sensitivity became independent of retinal illuminance. Similarly, at all levels of retinal illuminance contrast sensitivity increased in proportion to A when grating area (A) was smaller than critical area. Thereafter the increase saturated and contrast sensitivity became independent of area. Critical level of retinal illuminance increased in proportion to the spatial frequency squared. Critical area marking the saturation of spatial integration was constant at low spatial frequencies but decreased in inverse proportion to spatial frequency squared at medium and high spatial frequencies. The maximum contrast sensitivity obtainable by spatial integration in bright light increased at low spatial frequencies in proportion to spatial frequency, was constant at medium spatial frequencies, and decreased in inverse proportion to spatial frequency cubed at high spatial frequencies. The increase was due to the neural modulation transfer function of the visual pathways whereas the decrease was due to the optical modulation transfer function of the eye. The model explained 91-99% of the total variance of our contrast sensitivity data at various spatial frequencies.

Adult↗

PubMed2006

Prediction of serum total antioxidant activity from the concentration of individual serum antioxidants.

BACKGROUND: Redox mechanisms are implicated in the pathogenesis of many diseases and several assays of total antioxidant capacity (TAOC) have been reported. Large epidemiological databases contain information on individual serum antioxidants as well as disease-specific phenotypic data. However, antioxidants work co-operatively in biological systems and it is important to be able to translate individual antioxidant measures into those of global antioxidant defence. Models therefore need developing to quantify contributions made by individual species to global antioxidant defence. OBJECTIVE: To develop a predictive model that translates individual antioxidant concentrations into an index of TAOC, enabling interrogation of epidemiological databases that contain information about individual antioxidants, but not about TAOC. METHODS: Sera from 256 volunteers were simultaneously assayed for key antioxidants and TAOC by enhanced chemiluminescence (TAOC(ECL)). A predictive model was developed for serum TAOC using multiple linear regression analysis. RESULTS: The model explained 86% of TAOC(ECL) variability in serum. The strongest predictor of TAOC(ECL) was uric acid (1 SD increase associated with TAOC(ECL) increase of 103 micromol/l Teq-95% CI: 96.8-109), followed by vitamins A, C, E. CONCLUSIONS: The reported model represents a powerful tool for interrogating databases where individual serum antioxidant concentrations are known, and TAOC measures are required.

Antioxidants↗

PubMed2005

Role of complementary proteins in autoimmunity: an old idea re-emerges with new twists.

It has been suggested that complementary proteins are involved in autoimmunity through a network involving idiotype-anti-idiotype reactions termed 'autoantigen complementarity'. We propose that complementary proteins, which occur naturally or result from cellular dysfunction, might be more common than recognized currently. This implies that the role of complementary proteins in autoimmunity merits increasing investigation. The concept of complementary proteins is reviewed here and, also, new ideas are presented that underscore the role of open-reading frames in frame -1 of recognized genes in the production of complementary proteins (frame -1 is the reverse complement sequence of a gene that uses the antisense of the codons of frame +1). Furthermore, a novel role for palindromic sequences in autoimmunity and a new model explaining how abzymes and autoantigen complementarity might be related are proposed.

Amino Acid Sequence↗

PubMed2001

Preadolescent predictors of substance initiation: a test of both the direct and mediated effect of family social control factors on deviant peer associations and substance initiation.

A review of the literature suggests that early substance initiation is related to a variety of negative outcomes, including substance misuse or abuse in adolescence and adulthood. This study examines potentially modifiable predictors of early substance initiation, including both family and peer factors known to influence early initiation. A theoretically derived model of substance initiation was tested using structural equation modeling. Results indicate that both family and peer factors have an impact on early substance initiation when children in this sample were 11 and 12 years old. The model explained 60% of the variance in substance initiation. Prosocial family processes (rules, monitoring, and attachment) had a significant impact on child peer association, decreasing involvement with antisocial peers. These prosocial family processes had a significant negative effect on substance initiation even while modeling the influence of antisocial peers. Implications for drug use prevention practice are discussed.

Catchment Area, Health↗

PubMed2002

Mathematical analysis of dynamics of cardiac memory and accommodation: theory and experiment.

Decreasing the slope of the dynamic, but not conventional, restitution curves is antifibrillatory. Cardiac memory/accommodation underlies the difference. We measured diastolic interval (DI) and action potential duration (APD) in epicardial, endocardial, and Purkinje tissue from eight dogs. Consecutive 100-stimulus trains were given to study transitions between basic cycle lengths (BCL) ranging from 400 to 1,300 ms. (DI,APD) pairs aligned immediately on the line DI + APD = BCL (64/67) or oscillated (3/67). The shifting effect of up to 10 extrastimuli on restitution curves was also measured. These curves were fit with the equation APD = alpha + beta exp(-DI/tau), where alpha is asymptote, beta is drop, and tau is time constant. Linear regression of the parameters against the number of extrastimuli showed that premature and postmature stimuli decreased and increased alpha and beta and increased and decreased tau, respectively. Analysis of a mathematical model treating memory as an exponentially decreasing shift of restitution curves shows that oscillatory DI,APD is expected with large DeltaBCL, steep restitution slope, or increased cardiac accommodation. The model explains phase shifts and suggests a common mechanism for Purkinje and myocardial electrical alternans.

Animals↗

PubMed2003

How to find the real one (at the level of pre-mRNA splicing).

The mature mRNA always carries nucleotide sequences that faithfully mirror the protein product according to the niles of the genetic code. However, in the chromosome, the nucleotide sequence that represents a certain protein is interrupted by additional sequences. Therefore, most eukaryotic genes are longer than their final mRNA products. The human genome project revealed that only a tiny portion of sequences serves as protein-coding region and almost one quarter of the genome is occupied by non-coding intervening sequences. The elimination of these non-coding regions from the precursor RNA in a process termed splicing must be extremely precise, because even a single nucleotide mistake may cause a fatal error. At present, two types of intervening sequences have been identified in protein-coding genes. One of them, the U2-dependent or major-class is prevalent and represents 99% of known sequences. The other one, the so-called U12-dependent or minor-class of introns, occurs in much lesser amounts in the genome. The basic problem of nuclear splicing concerns i/ the molecular mechanisms, which ensure that the coding regions are correctly recognized and spliced together: ii/ the principles and mechanisms that guarantee the high fidelity of the splicing system; iii/ the differences in the excision mechanisms of the two classes of introns. We are going to present models explaining how intervening sequences are accurately removed and the coding regions correctly juxtaposed. The two splicing mechanisms will also be compared.

Exons↗

PubMedDate not supplied

[Relation between the excitatory synaptic currents and clamped somatic potential in the model of neuron with nonlinear dendrites].

The influence of the clamped somatic potential on the excitatory synaptic current (EPSC) was studied in the model of the dendrite with N-shaped instantaneous stationary current--voltage curve. Proximal EPSC diminish and become narrower with decreasing hyperpolarization or modest depolarization, distal EPSC increase and become wider, intermediately distant EPSC change insignificantly. Under increasing depolarization all the EPSC become significantly wider and larger. EPSC facilitate stable depolarization of the dendrites. When the dendrite is stable depolarized EPSC becomes very small and narrow, but it becomes larger and wider as the soma is hyperpolarized. EPSC becomes especially large and wide when the soma is hyperpolarized just to terminate the stable depolarization of the dendrite branch where the active synapses are located. The model explains certain phenomena which are difficult to understand by the theory of ohmic dendrites. New phenomena are predicted.

Dendrites↗

PubMedDate not supplied

[Respiratory function and cardiovascular risk factors. Research Group for the Integrated Community Control of Chronic-degenerative diseases in the Health District of Sezze -- Di.S.Co. -- Observational strategy to assess the community health status].

Within the Project Community Control of Chronic Diseases in the Health District of Sezze-Di.S.Co.-2940 men, aged 20-69 were examined between 1984 and 1987, and a pulmonary function test was performed together with the measurement of a number of cardiovascular risk factors. Blood tests, blood pressure, anthropometric measurements, ECG, spirometry and a questionnaire on life-style and diseases were available. The aim of this paper was to describe pulmonary function tests and to study their association with cardiovascular risk factors. Vital capacity (CV) and forced expiratory volume in one second (VEMS), adjusted by height were inversely related with age. Main cardiovascular risk factors were analysed in tertiles of CV and VEMS: fasting blood glucose, serum cholesterol, uric acid, haematocrit, diastolic blood pressure, number of cigarettes per day decreased going from the first to the third tertile, whilst HLD-cholesterol and alcohol consumption increased. Univariate and multivariate analysis showed an inverse relation of CV and VEMS with age, fasting blood glucose, number of cigarettes smoked per day, uric acid, heart rate, skinfold thickness whilst alcohol consumption and weight were inversely related. The models explained between 52% (VC) to 57% (VEMS) of the variance.

Adult↗

PubMed2002

Micromechanics of plant tissues beyond the linear-elastic range.

We investigated the relation between cell wall structure and the resulting mechanical characteristics of different plant tissues. Special attention was paid to the mechanical behaviour beyond the linear-elastic range, the underlying micromechanical processes and the fracture characteristics. The previously proposed model of reorientation and slippage of the cellulose microfibrils in the cell wall [H.-CH. Spatz et al. (1999) J Exp Biol 202:3269-3272) was supported and is here refined, using measurements of the changes in microfibrillar angle during straining. Our model explains the widespread phenomenon of stress-strain curves with two linear portions of different slope and sheds light on the micromechanical processes involved in viscoelasticity and plastic yield. We also analysed the velocity dependence of viscoelasticity under the perspective of the Kelvin model, resolving the measured viscoelasticity into functions of a velocity-dependent and a velocity-independent friction. The influence of lignin on the above-mentioned mechanical properties was examined by chemical lignin extraction from tissues of Aristolochia macrophylla Lam. and by the use of transgenic plants of Arabidopsis thaliana (L.) Heynh. with reduced lignin content. Additionally, the influence of extraction of hemicelluloses on the mechanical properties was investigated as well as a cell wall mutant of Arabidopsis with an altered configuration of the cellulose microfibrils.

Arabidopsis↗

PubMed2002

p38-avidity-ELISA: examination of herds experiencing epidemic or endemic Neospora caninum-associated bovine abortion.

An enzyme-linked immunosorbent assay (ELISA) was established to measure the avidity of bovine IgG directed against p38, a surface antigen (NCSRS2) of Neospora caninum tachyzoites. In the sera of dams intravenously infected with N. caninum NC-1, the p38-specific avidity increased from initially below 40% up to avidity indices between 50 and 80% after days 23 and 91 p.i. The p38-avidity-ELISA was used to examine various herds that had experienced endemic and epidemic N. caninum-associated bovine abortions. In herds with endemic abortion, generally high avidity indices of N. caninum-specific IgG were detected. This finding and the observation of an association between the seropositivity of dams and that of their offspring suggested a predominantly vertical transmission of the parasite among the animals of these herds, thus indicating chronic infection of these cattle. In contrast, for herds experiencing epidemic abortion: (i) an association regarding seropositivity of dams and their daughters could not be shown and (ii) a generally low avidity of p38-specific IgG in the sera from aborting dams was determined. This indicates recent postnatal transmission of N. caninum in these herds. A linear regression model explaining the avidity of p38-specific IgG was significantly influenced by the time span between sampling and the occurrence of the first abortion of the epidemic in herds with an N. caninum-associated abortion storm. Another factor significantly contributing to the model was the proportion of dams at risk that had aborted in the herds (i.e. the severity of the abortion epidemic). A possible explanation for this observation is that herds experiencing heavy abortion are sampled earlier after the onset of the epidemic than others that have a less severe abortion storm.

Abortion, Veterinary↗

PubMed1998

An intragenic suppressor of the Arabidopsis floral organ identity mutant apetala3-1 functions by suppressing defects in splicing.

The Arabidopsis floral organ identity gene APETALA3 (AP3) specifies the identity of petals and stamens in the flower. In flowers mutant for the temperature-sensitive ap3-1 allele, the petals and stamens are partially converted to sepals and carpels, respectively. ap3-1 contains a single nucleotide change in the AP3 gene that alters both an amino acid in the AP3 protein and the 5' splice consensus site for intron 5. Surprisingly, the Ap3-1 mutant phenotype is not due to the missense mutation but instead is due to defects in splicing; specifically, exon 5 is frequently skipped by the splicing machinery at the restrictive temperature. In a screen for suppressors of ap3-1, we isolated an intragenic suppressor, ap3-11, that functions to suppress the splicing defects of ap3-1. Using a reverse transcriptase-polymerase chain reaction assay, we demonstrate that the percentage of full-length exon 5-containing AP3 RNAs correlates with the phenotype of the flowers in both ap3-1 and ap3-11. Rather surprisingly, the ap3-11 suppressor mutation is located in intron 4. One model explaining the function of ap3-11 is that the ap3-11 suppressor creates a novel branch point sequence that causes exon 5 to be more frequently recognized by the splicing machinery. The identification of such a suppressor strongly suggests that exon-scanning models of intron-exon recognition are operative in plants.

Arabidopsis↗

PubMed1993

The mathematical modelling of human culture and its implications for psychology and the human sciences.

Recent years have seen the growth of a new and exciting field of theoretical research concerned with the mathematical modelling of human culture, and of its interaction with genetics. Drawing on analogies between genetic and cultural processes, mathematically sophisticated biologists have used population genetics models as the basis for the development of analogous models of cultural transmission, cultural evolution and gene-culture co-evolution. These models are designed to describe and analyse the diffusion of cultural traits through populations, under the influence of various cultural and evolutionary forces. They have already been applied to address many problems of interest to psychologists. Here I present an introduction to these models, explaining the mathematics in simple terms, and giving examples of the work of leading theorists. I go on to discuss the findings of most relevance to psychology, critically analysing the most important conclusions. Finally, I suggest some areas of psychology in which these models might usefully be applied. I argue that these models constitute a major theoretical innovation, and that there is considerable potential for their application in psychology.

Behavior↗

PubMed2001

A neural model of smooth pursuit control and motion perception by cortical area MST.

Smooth pursuit eye movements (SPEMs) are eye rotations that are used to maintain fixation on a moving target. Such rotations complicate the interpretation of the retinal image, because they nullify the retinal motion of the target, while generating retinal motion of stationary objects in the background. This poses a problem for the oculomotor system, which must track the stabilized target image while suppressing the optokinetic reflex, which would move the eye in the direction of the retinal background motion (opposite to the direction in which the target is moving). Similarly, the perceptual system must estimate the actual direction and speed of moving objects in spite of the confounding effects of the eye rotation. This paper proposes a neural model to account for the ability of primates to accomplish these tasks. The model simulates the neurophysiological properties of cell types found in the superior temporal sulcus of the macaque monkey, specifically the medial superior temporal (MST) region. These cells process signals related to target motion, background motion, and receive an efference copy of eye velocity during pursuit movements. The model focuses on the interactions between cells in the ventral and dorsal subdivisions of MST, which are hypothesized to process target velocity and background motion, respectively. The model explains how these signals can be combined to explain behavioral data about pursuit maintenance and perceptual data from human studies, including the Aubert--Fleischl phenomenon and the Filehne Illusion, thereby clarifying the functional significance of neurophysiological data about these MST cell properties. It is suggested that the connectivity used in the model may represent a general strategy used by the brain in analyzing the visual world.

Animals↗