A new model to explain the redundant-signals effect.
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Results for “Model explainability”
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A clinical and pharmacological model for explaining response to desmopressin.
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Adult↗
On vestibular nystagmus. Definition and identification of nystagmus and a model to explain the genesis of vestibular nystagmus.
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Cold Temperature↗
[Experimental and pathological models that explain the regulation of cellular migration and axon's orientations].
Since Cajal discovery of nerve growth cones and their role in the growth, metabolism and destination of the axon in 1890 numerous studies have corroborated with more sophisticated techniques his original findings and ideas. The use of modified Golgi staining, drawing from the camera lucida in 2 combination with electron microscopy and t retrograde biochemical markers have helped to identify the neuronal sites of synapsis. Dynamic studies of the nerve growth cones using time-lapsed video microscopic images of living neuroblast in t culture or the intact animal have demonstrated their protactil and retractile membranes and exploratory filipodia properties. Interaction between growth cone membrane receptors and different molecules along the migrating axon determine also its final destination. Finally the role that genes play on neuronal migration and in guiding the axons to reach their targets have been identified in patients with Kallmann syndrome, a migrational disorder of olfactory axons and hypothalamic gonadotropic hormone-releasing hormone with absent gene at Xp22.3 locus manifested by anosmia and hypogonadotropic hypogonadism.
Axons↗
Noisy templates explain area summation.
The noisy template model is a variant of an ideal detector for a signal known except for contrast. The ideal detector cross-correlates the stimulus with a normalised template which is matched to the known signal pattern. The noisy template model simply adds noise to the matched template every time it is cross-correlated with the signal. This paper outlines the predictions of the noisy template model for area summation. The noisy template model explains Piper's Law, as does the ideal-observer, but it also explains critical area phenomena and the lack of area summation for contrast discrimination.
Computer Simulation↗
Clinical and pathophysiological observations in migraine and tension-type headache explained by integration of vascular, supraspinal and myofascial inputs.
A vascular-supraspinal-myogenic (VSM) model for pain in migraine based on our previous clinical and pathophysiological observations is proposed. According to the model, perceived pain (headache) intensity is determined by the sum of nociception from cephalic arteries and pericranial myofascial tissues converging upon the same neurons and integrated with supraspinal effects (usually facilitating). Vascular input predominates over myofascial input in migraine, whereas significance of supraspinal facilitation is difficult to estimate. The importance of these 3 effects may vary between patients and in the same individual with time. The model is in accordance with recent experimental studies showing convergence of somatovisceral afferents upon n. caudalis neurons. Also, long term potentiation due to nociceptive activation and sensitization of neurons to input from wider areas and non-nociceptive stimuli are relevant to our model. In tension-type headache, nociception is primarily myofascial, but vascular input cannot be disregarded. Supraspinal facilitation probably plays a large, sometimes dominant role (the MSV model). The model explains much of the complexity of the clinical picture of these disorders as well as their tendency to overlap and to change into one another. Also, a number of pathophysiological observations such as why muscles are tender during migraine, why trigger-point injection may cure migraine attacks and why chronic tension-type headache is often associated with episodes of pulsating pain, can be explained. The model gives a rational explanation of empirically developed, internationally accepted, multimodal treatment strategies for migraine and tension-type headache. It may thus serve a useful purpose in explaining the disorder to patients. Finally, the model points to several avenues of future research in animals and man.
Animals↗
High-affinity binding of cytochalasin B to the B-end of F-actin loses its inhibitory effect on subunit exchange when the bound nucleotide is ADP.
We investigated the mode of binding of cytochalasin B (CB) to F-actin in an ADP-solution with and without inorganic phosphate (Pi). In the presence of Pi (20 mM), a filament of F-actin had a single high-affinity CB binding site (Kd = 1.4 nM), just like in the case of an ATP-solution [Kd = 5.0 nM: Suzuki, N. & Mihashi, K. (1991) J. Biochem. 109, 19-23]. But in the absence of Pi, there were two low-affinity (Kd = 200 nM) CB binding sites as well as one high-affinity site (Kd = 1.6 nM). We determined the concentration of CB necessary for half-maximal inhibition of growth or shortening of F-actin (Ki) using of pyrene-labeled actin. We obtained Ki = 80 nM for growth and Ki = 800 nM for shortening in the presence of ATP. The addition of Pi to the ATP-solution reduced Ki for growth to 9 nM. We propose a model explaining these results. In the model, high-affinity CB binding to the terminal subunit dimer can inhibit subunit exchange at the B-end only when the terminal subunits bind ATP or ADP.Pi. When the terminal subunits bind ADP, additional low-affinity CB bindings to the terminal subunits are needed to inhibit the subunit exchange.
Actins↗
How the basal ganglia use parallel excitatory and inhibitory learning pathways to selectively respond to unexpected rewarding cues.
After classically conditioned learning, dopaminergic cells in the substantia nigra pars compacta (SNc) respond immediately to unexpected conditioned stimuli (CS) but omit formerly seen responses to expected unconditioned stimuli, notably rewards. These cells play an important role in reinforcement learning. A neural model explains the key neurophysiological properties of these cells before, during, and after conditioning, as well as related anatomical and neurophysiological data about the pedunculopontine tegmental nucleus (PPTN), lateral hypothalamus, ventral striatum, and striosomes. The model proposes how two parallel learning pathways from limbic cortex to the SNc, one devoted to excitatory conditioning (through the ventral striatum, ventral pallidum, and PPTN) and the other to adaptively timed inhibitory conditioning (through the striosomes), control SNc responses. The excitatory pathway generates CS-induced excitatory SNc dopamine bursts. The inhibitory pathway prevents dopamine bursts in response to predictable reward-related signals. When expected rewards are not received, striosomal inhibition of SNc that is unopposed by excitation results in a phasic drop in dopamine cell activity. The adaptively timed inhibitory learning uses an intracellular spectrum of timed responses that is proposed to be similar to adaptively timed cellular mechanisms in the hippocampus and cerebellum. These mechanisms are proposed to include metabotropic glutamate receptor-mediated Ca(2+) spikes that occur with different delays in striosomal cells. A dopaminergic burst in concert with a Ca(2+) spike is proposed to potentiate inhibitory learning. The model provides a biologically predictive alternative to temporal difference conditioning models and explains substantially more data than alternative models.
Animals↗
An attempt at an analysis of the factors determining the time course of the glutamate response in the crayfish neuromuscular junction.
An attempt was made to analyse the factors which might determine the time course of the end-plate current. The end-plate current was measured by clamping the membrane potential of the crayfish muscle fiber. The calculated glutamate-induced current was in good agreement with the observations obtained, suggesting that the presented kinetic model explained well the practical phenomenon. The kinetic model could be applied also to explain the depolarization change induced by prolonged application of glutamate. The semilogarithmic plots of the falling phase of calculated glutamate-induced currents gave an approximately straight line. The slope of the line yielded an apparent desensitization rate constant, and the relationship between the true and apparent desensitization rate constants was determined, but it was suggested that the desensitization rate could not be determined from the slope of the decay of glutamate-induced current alone.
Animals↗
A new model for understanding the role of environmental factors in the origins of chronic illness: a case study of type 1 diabetes mellitus.
There is a need for a new pathophysiological model explaining and linking the role of numerous non-genetic factors believed to contribute to origins of many chronic physical diseases. This article presents a theoretical model for explaining the confusing and often contradictory findings regarding the role of environmental influences in type 1 diabetes, a disease that has been widely studied, for which clear diagnostic criteria exist, and for which development of effective prevention strategies represents significant challenges. The model is formulated from the large database of research regarding increasing understanding of the interaction between environmental factors, physiology, and autonomic regulatory function. Data is integrated from research in the fields of the experience-dependent maturation of the nervous system and the neurophysiology of traumatic stress to demonstrate how disruptions in early bonding and attachment, including adverse events such as traumatic stress, are capable of causing: (1) long-term imbalances in autonomic regulatory function and (2) relative dominance of sympathetic or parasympathetic activity. The proposed model of autonomic dysfunction suggests that ongoing mechanisms promoting high glucose in the context of decreasing insulin production in type 1 diabetes represent a state of relative sympathetic dominance influenced by environmental factors affecting autonomic, immune and endocrine systems during critical period programming. The model further identifies a link between the many seemingly unrelated non-genetic risk factors, and appears capable of explaining contradictions and enigmas in epidemiological and clinical studies regarding non-genetic origins of type 1 diabetes, including the role of stress, variation in age of onset, and duration of the preclinical phase.
Age Distribution↗
Models of intracellular transport and evolution of the Golgi complex.
We have performed a systematic analysis of models explaining the mechanisms of the intracellular biosecretory transport. The models assessed include not only those based on one mechanism (the dissociation model (and its individual case, the vesicular model), the progression model (and its individual cases, the cisterna maturation/progression and the carrier maturation models), and the lateral diffusion model (and its individual case, the bolus model), but also combined models of transport (the percolating-vesicles model and the synthetic model), including several transport mechanisms. Most of these models are not able to explain recent data on the evolution of genes involved in intracellular transport and Golgi evolution. The carrier maturation model proposing that fusion of the large cargo domain with the distal (closer to the plasmalemma) compartment precedes fission of the domain from the proximal compartment exhibits the best performance in correlation with the available information on evolution of the biosecretory pathway.
Biological Evolution↗
An experimental study of behavioural group size effects in tammar wallabies, Macropus eugenii.
As animals aggregate with others, the time they allot to social and nonsocial activities changes. Antipredator models of vigilance and foraging group size effects both predict a nonlinear relationship between group size and the time allocated to behaviour. Group size effects were experimentally studied in captive adult female tammar wallabies, a small macropodid marsupial, by increasing group size from 1 to 10. Tammars foraged more, looked less, groomed more, engaged in more aggressive interactions and moved about less as group size increased. Nonlinear regression models explained more variation in the time allocated to foraging, looking, locomotion and affiliative behaviour than linear models. Variation in self-grooming and aggression was better explained by linear models. Wallabies lay down significantly more, and walked significantly less, as group size increased: these relationships were significantly nonlinear. Thus, changes in perceived predation risk, which are characterized by nonlinear relationships, explain tammar wallaby group size effects for most activities. These results support the assertion that predation has played an important role in macropodid social evolution. Moreover, the findings suggest that conservation biologists should pay particular attention to group size when translocating or reintroducing endangered macropodids. Copyright 1999 The Association for the Study of Animal Behaviour.
Journal Article↗
Multilevel modelling of longitudinal cephalometric data explained for orthodontists.
Multilevel modelling of longitudinal data is an important new statistical technique. In this article some of the basic concepts and ideas of multilevel modelling are explained. The model is introduced by showing how individual and average growth can be modelled. The intercept, linear and quadratic coefficient, between and within variance, fixed and random part, and other concepts of multilevel modelling are explained. Attention is also given to the reading of statistical tables of the results of multilevel analysis. In the conclusion some of the advantages of multilevel modelling of cephalometric data are mentioned.
Aging↗
Bone turnover and body weight relationships differ in normal-weight compared with heavier postmenopausal women.
Low body weight is associated with increased risk for fractures, whereas higher body weight has been shown to be protective against osteoporosis. This study evaluated whether body weight plays a role regulating bone turnover and mass in normal-weight (body mass index (BMI) <25 kg/m2), overweight (BMI 25-29.9 kg/m2) and obese (BMI> or =30 kg/m2) postmenopausal women who were either receiving hormone replacement therapy [HRT(+)] or not [HRT(-)] (total of six groups). Body weight, BMI, total body bone mineral content (TBBMC), and markers of bone formation (serum osteocalcin) and bone resorption (urinary pyridinoline (PYD) and deoxypyridinoline) were retrospectively analyzed in 210 postmenopausal women. The mean age was 67+/-6 years, with mean body weight of 70.8+/-14.2 kg, ranging from 45.0 to 115.5 kg. Body weight was positively correlated with TBBMC ( r=0.50, p<0.0001). There was a lower TBBMC and higher bone formation rate in normal-weight than obese HRT(-) women, but in women taking HRT there were no differences between BMI categories. In addition, in normal-weight HRT(-) women only, PYD and body weight showed a negative correlation (r=-0.39, p=0.01). Among normal-weight, but not overweight or obese subjects, we observed higher TBBMC and lower bone turnover in the HRT(+) compared with the HRT(-) group. Regression models explained 36% of the variance in TBBMC, mainly through body weight. Additional models could only explain 11-15% of the variance in bone turnover. Taken together, these data suggest that among normal-weight but not obese postmenopausal women, higher bone turnover is associated with lower bone mass, and that only normal-weight women show a different bone turnover profile with HRT treatment. Body weight should be considered an important factor in bone metabolism with relevant clinical implications.
Aged↗
Predictors of good compliance in adolescents with epilepsy.
The purpose of this paper was to describe the factors that predict compliance in adolescents with epilepsy. Altogether 300 individuals aged 13-17 years were randomly selected from the Finnish Social Insurance Institution's register. Every fifth person on the list was included in the sample. Seventy-seven per cent (N= 232 ) of the selected adolescents with epilepsy returned the questionnaire. The data were analysed with SPSS software. Using the logistic regression model, the compliance of adolescents with epilepsy was predicted on the basis of support from physician and parents, motivation and the disease not being a threat of social well-being. The most powerful predictor was support from the physician. The likelihood of adolescents supported by their physicians complying with their health regimens was 10.56-fold compared with the adolescents who did not receive support from their physicians. Another powerful predictor was support from parents. The adolescents who received support from their parents complied with the health regimens with a 10.47-fold likelihood compared with adolescents who did not receive support from their parents. Adolescents with good motivation were 9.77 times more likely to comply than adolescents who did not have good motivation. Adolescents who did not feel the disease to be a threat to their social well-being complied with health regimens with an 8.38-fold likelihood compared to those who felt the disease to be a threat to social well-being. The value of the -2Log likelihood was 64.68 and the goodness of fit index was 214.735. The value of Nagelkerke was 0.893, which indicates that the logistic regression model explains 89% of the variance. The model predicts correctly 97% of compliance in adolescents showing good compliance. These values show the logistic regression model to be good and to match well with the data.
Adolescent↗
Minimizing fatigue during repetitive jobs: optimal work-rest schedules.
Twenty women were asked to generate forces using a dynamometer that were consistent with one of three different work-rest schedules (a low-, medium-, and high-force schedule). Each work-rest schedule consisted of 6 identical blocks of 10 work-rest cycles. Each of the 10 work-rest cycles lasted 1 min. The first work-rest cycle in each block consisted of a 6-s maximal voluntary contraction and a 54-s rest. The remaining 9 work-rest cycles in each block consisted of a submaximal contraction and a rest period. The desired force of the submaximal contraction, the length of this contraction, and the duration of the rest period remained constant within schedules but varied across schedules. The amount of physiological work was kept constant among schedules. The fatigue that developed in the medium-force schedule was significantly lower than that developed in either the low- or high-force schedule. A model was developed that predicted the amount of fatiguable strength at the beginning and end of each contraction of a work-rest cycle. When fit to the results from the experiment, the model explained 94% of the variance. The model can be used to predict the work-rest schedule that minimizes fatigue in a given repetitive job, thereby potentially increasing productivity and reducing the incidence of cumulative trauma disorders.
Adult↗
Phenotypic and genetic effects on feed intake of laying hens in different years.
Feed intake from 21 to 40 wk and from 41 to 60 wk of age of brown egg layers was analyzed. The full model contained BW, egg mass (EM) output, BW change (BWCH), and age at first egg as covariates in addition to effects of plumage condition class, sire, and dam. A reduced model contained the covariates only. Between 905 and 1,161, and 880 and 1,119 hens were available in the first and second periods, respectively. Averaged over 6 yr the full model explained 84 and 77%, the reduced model 73 and 63%, respectively, of the variance in feed consumption in the two periods. Regression coefficients for BW showed only a small variation between years as well as between periods. Variation was larger for the coefficients of EM and of BWCH. Larger coefficients were observed in the first period for both traits. The sequence of entering the reduced equation in a stepwise procedure was always BW, EM output, then BWCH. Averaged over 6 yr, the relative contribution of BW by its own to the accuracy of the regression model, was 68 and 60% in the two periods. Egg mass output then added 25 and 39%, and BWCH 7 and 2% in the first and second periods, respectively. The predictive value of the covariates changed with increasing age of the hens. A high average heritability of .48 could be estimated for the residual feed intake in both periods. This suggested enhanced selection response for efficiency.
Animals↗
The etiopathogenesis of schizophrenias.
There is no generally accepted model explaining the aetiopathogenesis of schizophrenias. In recent years, hypotheses with a focus on single aspects of neurotransmission, single major genetic loci or single brain areas were predominating. Now, these different approaches converge to systemic models including neurotransmission, genetic changes and neurodevelopmental malformation of brain structures. Such systemic models will explain more aspects of schizophrenias than the recent confined hypotheses.
Animals↗