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PubMed2000

Simplicity versus likelihood in visual perception: from surprisals to precisals.

The likelihood principle states that the visual system prefers the most likely interpretation of a stimulus, whereas the simplicity principle states that it prefers the most simple interpretation. This study investigates how close these seemingly very different principles are by combining findings from classical, algorithmic, and structural information theory. It is argued that, in visual perception, the two principles are perhaps very different with respect to the viewpoint-independent aspects of perception but probably very close with respect to the viewpoint-dependent aspects which, moreover, seem decisive in everyday perception. This implies that either principle may have guided the evolution of visual systems and that the simplicity paradigm may provide perception models with the necessary quantitative specifications of the often plausible but also intuitive ideas provided by the likelihood paradigm.

Gestalt Theory↗
PubMed1994

The afferent circulation of the transplanted liver during the recirculatory phase in dogs.

The relationship between the changes in portal venous and hepatic arterial blood flows, e.g. the interaction of the two vascular systems in the liver always was a much disputed question, although it has tremendous significance in the practice of transplantation, and the explanation has been known since 1981, when Lautt published the so-called "adenosine washout theory" /9/. According to our earlier observations the decrease of portal pressure of flow generally and consistently led to an increase in hepatic artery flow. At the same time, changes in hepatic artery flow or pressure seemed to produce only inconsistent effects on the portal circulation. In the present experiments liver transplantations were carried out on mongrel dogs by Starzl's method /14/. Electromagnetic flow probes were placed on the hepatic artery and the portal vein before removal of recipient's liver, and after completion of all vascular anastomoses of newly inserted liver, e.g. in the recirculatory phase of OLTX. The flow probes were connected to Hellige electromagnetic flowmeter, portal venous and systemic arterial pressures were recorded too. The control HAF was 241 +/- 23 ml/min, the average PVF was 517 +/- 47 ml/min before removal of the recipient's liver. In the recirculatory phase the HAF increased to 414 +/- 39 ml/min, by 71 +/- 12% (p < 0.001). The PVF decreased in most animals after OLTX. The decrease was in average -40.2 +/- 3.5% (p < 0.001). The THBF calculated by adding the HAF and PVF showed a small, but not significant decrease during recirculation. The control THBF was 758 +/- 50 ml or 39.0 +/- 3.1 ml/min/kg. In the recirculatory phase 754 +/- 48 ml/min HBF could be measured, respectively. The systemic arterial pressure slightly decreased, portal vein pressure rose in most animals after OLTX, accordingly there was a substantial increase of portal inflow resistance and of prehepatic arteriolar resistance, decrease of hepatic arterial resistance. The decrease of PVF after OLTX can be explained by a progressive fluid accumulation in the liver parenchyma and increased sinusoidal and portal inflow resistance. The prolonged and continuous increase of hepatic artery flow during recirculatory phase of OLTX may be due to the decrease of portal flow. The exact mechanism, by which a change in portal flow leads to arteriolar dilatation, can be most probably explained by "adenosine washout theory" of Lautt.

Animals↗
PubMed2000

Novel hotspot detector software reveals a non-CpG hotspot of germline mutation in the factor IX gene (F9) in Latin Americans.

Two-base substitutions at each of two nucleotides in the factor IX gene (F9), but not part of CpG dinucleotides, were recently reported in a small population sample collected in Mexico, a significant observation of recurrent sites ("hotspots") of mutation (P=0.00005). When these new data were combined with previously collected mutation data into two progressively larger and inclusive Latin American samples, additional mutations were observed at one recurrent site, nucleotide 17747, and an additional recurrent nucleotide was observed such that the recurrent nucleotides in these larger samples were also significant (P=0.0003 and 0.0003). In contrast, in three non-Latin American control samples, there was at most only one nucleotide that recurred only once, most likely a chance recurrence (P>/=0.5). When the significance of substitutions was analyzed at each recurrent nucleotide individually, nucleotide 17747 was shown to be a significant recurrent nucleotide by itself in all the Latin American population samples (P</=0.02). Furthermore, a standard statistical comparison of mutation frequencies in the previously collected data alone confirmed that the frequency of mutation at nucleotide 17747 is significantly higher in Latin Americans than in all other populations combined (P=0.01). Thus, nucleotide 17747 is a germline mutation hotspot in F9 specific to Latin American populations. This may be the first evidence for population-specific effects on germline mutation that causes human genetic disease. The significance of the observed recurrent sites was analyzed using new software called Hotspot Detector which is capable of detecting significant recurrent sites in small samples, extending the sensitivity of F9 as a human germline mutagen test. Hotspot Detector uses a Monte-Carlo simulation method that was validated by comparing its results with those from an exact probability formula derived from statistical theory.

CpG Islands↗
PubMed2003

Entropy and information in flagellar axoneme cybernetics: a radial spokes integrative function.

Radial spokes and the consequences of their relationships with the central apparatus seem to play a very important role in the regulation of axonemal activity. We modeled their behavior and observed that it appears to differ in the cilium and the flagellum with respect to the development of bending as a function of time. Specifically, our calculation raises the question of the real function of the radial spokes in the regulation of the axoneme, because a given curvature of the flagellar axoneme may correspond to two opposite of their tilts. The stable nil/low amplitude shear points that we had characterized along the flagellum allowed us to describe their axoneme as a series of modules [Cibert, 2002: Cell Motil. Cytoskeleton 51:89-111]. We observed that a nil/low shearing point moves along each module during beating when a new bend is created at the base of the flagellum [Cibert, 2001: Cell Motil. Cytoskeleton 49:161-175]. We propose that the structural gradients of isoforms of tubulin could be basic verniers that act as structural references for the axonemal machinery during the beating. This allowed us to interpret the axonemal organization as a segmented structure, that could be analyzed according to the complexion(1) theory and Shannon's information theory, which associate entropy and probability in the creation of information. The important consequence of this interpretation is that regulation of the axonemal machinery appears to be due to the upstream and downstream cross-talk between the axonemal segments that do not involve any dedicated integrative structure but depend on the energy level of the entire length of each module.

Biomechanical Phenomena↗
PubMed1996

Tumour progression: random mutations or an integrated survival response to cellular stress conserved from unicellular organisms?

The current paradigm states that cancer progression is caused by random independent mutations, each selected for its survival advantages. The accelerated rates of phenotypic changes, the pleiotropic effect of several genes involved in progression--which need not be necessarily mutated for inducing the observed changes in cancer cell behaviour--lead us to propose an alternative hypothesis. Malignant progression might be a result of the unveiling of a cell-survival program, induced by various aggressions in the same way as the SOS system is induced and regulated in bacteria. This hypothesis depends on the homology between several genes involved in cancer progression (such as bcl2, mdm2, the mismatch repair genes, the heat shock protein genes, the pleiotropic resistance genes, the telomerase gene ...) and several genes involved in the survival of prokaryotes and eukaryotes under stress. The development of multicellular organisms could not take place without the building of a control program, exemplified by the so-called anti-oncogenes. However, this control program had to integrate some weaknesses, in order to allow for embryogenesis, growth, and wound healing. These weaknesses, neutral from an evolutionary point of view--since most cancers are sporadic and kill their hosts long after the birth of the offspring--are exploited by the survival program of individual cells, inherited from the genome of prokaryotes and unicellular eukaryotes, and repressed but not suppressed in animals. If this theory is true, it is probable that (i) no anti-oncogenes will be found in unicellular organisms, (ii) the sensitivity to mutations will be higher in genes involved in proliferation and in anti-oncogenes such as p53 and Rb, than in genes not involved in the cancer process, (iii) a process of transfer of genetic information exists in cancer cells as it exists in bacteria. The identification of the genes governing the survival program could lead to new therapeutic approaches.

Animals↗
PubMed1988

The maintenance of transposable elements in natural populations.

Models of the maintenance of transposable elements in randomly mating host populations are reviewed. It is shown that the data on the distribution of copy numbers between individuals are largely concordant with what is expected on the basis of the Mendelian transmission of elements. The role of regulation of rates of transposition, and of various modes of natural selection, in maintaining an equilibrium in copy numbers in the face of transpositional increase in copy number is discussed. Tests for the role of selection against insertional mutations and against chromosome rearrangements induced by exchange between homologous elements located at nonhomologous chromosome locations are discussed. Reasons for expecting elements to accumulate in chromosome regions where crossing over is restricted are discussed, and data suggesting the existence of such an effect are described. Theory and data on the probability distribution of element frequencies at individual chromosomal sites are described. It is concluded that the available population data are consistent with the notion that element abundances are largely controlled by the interaction of transpositional increase in copy number with opposing forces.

Animals↗
PubMed1992

Orientation of Aplysia californica to distant food sources.

The behavior of the marine mollusc Aplysia was examined under different experimental conditions designed to determine the food searching strategy of the animals. In a small, open field tank with still water, the animals took an average of 42 min to find a piece of seaweed, even though the stimulus was never located more than 30 cm away from the animal. Observations of the animals indicated that their search was not directed, without a clear tendency towards the food, and during the course of a search, they often crawled through most of the area of the tank. The search time, the distance travelled, and the strategy of the search of the animals was similar for different types of seaweed. If animals were aroused into activity by the presence of seaweed extract, the time for them to contact a piece of odorless glass fiber paper in the open field was not significantly different than that for a piece of seaweed. The probability at which the animals contacted the seaweed, as a function of the distance travelled, resembled the detection probability determined according to a theory of random search. We thus propose that the aroused animals move in a random pattern until they are very close to the food. This strategy can be advantageous in still water since chemicals do not provide distinct gradients that can serve as cues for chemotactic orientation from distances greater than a few centimeters from the source. In a Y-maze in still water, Aplysia did not perform above chance in selecting the arm that contained the seaweed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Familial subluxation of the metacarpophalangeal and proximal interphalangeal joints of the little finger in two consecutive siblings: the "serpentine little finger".

Two consecutive siblings, both males, presented with congenital curly little finger ('serpentine finger') caused by subluxations at the metacarpo-phalangeal and the proximal interphalangeal joints. Literature on this phenomenon is scant, and to the best of the authors' knowledge it is probably a new entity. A theory of the possible aetiology is presented.

Child↗
PubMed1983

Coronary heart disease risk factors in bus and truck drivers. A controlled cohort study.

Fifty-two bus and truck drivers and a control group of 52 male industrial workers were studied with regard to risk factors for coronary heart disease (CHD) as well as some psycho-social and occupational indicators. The main results were: higher mean values for serum cholesterol, serum triglycerides and blood pressure in the driver group, indicating a markedly higher risk of CHD in the driver group. The two groups were matched for age, socio-economic status, dietary habits, smoking habits and alcohol consumption. In the study the groups were found to be equal as regards CHD-inheritance, physical activity in leisure time, and relative body weight, W/H2. No CO could be traced in the vehicles. The psycho-social and occupational indicators showed considerable differences. The average score for the exposure factor "tempo/time-limit/urgency in job" was 50% higher, and the number of persons with the characteristic "type-A coronary-prone behaviour" was 30% higher in the driver group than in the control group. The difference in blood lipids and blood pressure increased with age. It is suggested that the higher CHD-risk in the driver group is associated with two factors: (1) greater psychic pressure in the working situation; (2) the selection of more type-A persons to driver occupations. A probable, but not commonly accepted theory, is that these psychosocial indicators may influence the traditional risk factors in a harmful way.

Adult↗
PubMed2000

Venous valve station changes in "primary" and postthrombotic reflux: an analysis of 149 cases.

The purpose of this study was to analyze valve station changes noted during venous valve reconstruction and the associated outcome. One hundred and forty-nine valve reconstructions were available for analysis at the time of surgical exploration; the venous valve was graded according to valve station changes (VS grades) from zero through six. Ascending venography was analyzed by a similar grading system and the two methods were compared. The results of this analysis showed that valve station wall changes are frequently present in patients with deep venous reflux and pose technical challenges during valve reconstruction; the outcome, however, appears unaffected. Grade 0 to 1 valve station changes are predominantly due to "primary" reflux, with an occasional instance of postthrombotic etiology. Grade 2 or 3 valve station changes are roughly evenly divided between phlebosclerosis of primary reflux and postthrombotic etiologies. The mechanism of onset of reflux with preservation of valve cusps in the latter group of postthrombotic cases is probably different from currently accepted theories of evolution of postthrombotic changes. Postthrombotic valve damage is variable, and the valve station anatomy may be sufficiently preserved in some patients to allow direct valve repair.

Endothelium, Vascular↗
PubMed1989

Disaggregate model of highway accident occurrence using survival theory.

The analysis of discrete accident data and aggregate exposure data frequently necessitates compromises that can obscure the relationship between accident occurrence and potential causal risk components. One way to overcome these difficulties is to develop a model of accident occurrence that includes accident and exposure data at a mathematically consistent disaggregate level. This paper describes the conceptual and mathematical development of such a model using principals of survival theory. The model predicts the probability of being involved in an accident at time t given that a vehicle has survived until that time. Several alternative functional forms are discussed including additive, proportional hazards and accelerated failure time models. Model estimation is discussed for the case in which both accident and nonaccident trips are included and for the case with only accident data. As formulated, the model has the distinct advantage of being able to consider accident and exposure data at a disaggregate level in an entirely consistent analytic framework. A conditional accident analysis is undertaken using truck accident data obtained from a major national carrier in the United States. Model results are interpretable and generally reasonable. Of particular interest is that segmenting accidents in several categories yields very different sets of significant parameters. Driver service hours seemed to most strongly effect accident risk: regularly scheduled drivers who take frequent trips are likely to have a reduced risk of an accident, particularly if they have a longer (greater than eight) number of hours off-duty just prior to a trip.

Accidents, Traffic↗
PubMed1992

The number of symbiotic origins of organelles.

Mitochondria and chloroplasts both originated from bacterial endosymbionts. The available evidence strongly supports a single origin for mitochondria and only somewhat less strongly a single, slightly later, origin for chloroplasts. The arguments and evidence that have sometimes been presented in favor of the alternative theories of the multiple or polyphyletic origins of these two organelles are evaluated and the kinds of data that are needed to test more rigorously the monophyletic theory are discussed. Although chloroplasts probably originated only once, eukaryotic algae are polyphyletic because chloroplasts have been secondarily transferred to new lineages by the permanent incorporation of a photosynthetic eukaryotic algal cell into a phagotrophic protozoan host. How often this has happened is much less clear. It is particularly unclear whether or not the chloroplasts of typical dinoflagellates and euglenoids originated in this way from a eukaryotic symbiont: their direct divergence from the ancestral chloroplast cannot be ruled out and indeed has several arguments in its favor. The evidence for and against the view that the chloroplast of the kingdom Chromista was acquired in a single endosymbiotic event is discussed. The possibility that even the chloroplast of Chlorarachnion might have been acquired during the same symbiosis that created the cryptomonad cell, if the symbiont was a primitive alga that had chlorophyll a, b and c as well as phycobilins, is also considered. An alga with such a combination of pigments might have been ancestral to all eukaryote algae.

Biological Evolution↗
PubMed1979

Selectivity and rejectivity in cancer metastasis.

In cancer metastasis, "selectivity" denotes the formation of secondary tumor in an organ in such a manner that its localization pattern is peculiar. The opposite phenomenon should be recognized and called "rejectivity". In man, carcinomas appear to spread selectively to the umbilicus, whereas lymphomas seem to reject that site. In all probability, recognition of the twin theory of selectivity and rejectivity will stimulate research on cancer dissemination.

Humans↗
PubMed1987

A stochastic process approach to the development of atheroma.

This study aims at formulating a dynamic model of particle sedimentation as applied to lipoprotein deposition during atheroma progression. The basic assumption is that all particles are identical and that the number of sedimented particles is relatively great. It is hypothised that sedimentation of a given particle is random; according to the theory of stochastic processes, the probability of a certain number of particles to sediment or deposit changes with time. The stochastic approach may explain some aspects of atherosclerosis development, i.e. its progression or regression.

Animals↗
PubMedDate not supplied

Morphometry of the microvillous membrane of the human placenta in maternal diabetes mellitus.

The syncytiotrophoblast microvillous membrane of the human placenta has been investigated with quantitative analyses in a group of placentae from diabetic mothers, these placentae being compared to a group of normal placentae. This study has shown that, in the placentae of the diabetic mothers, there was a significant increase in the surface density of the microvilli and in the microvillous surface enlargement factor as compared to those of the controls. Consequently, it has demonstrated that the already large villous surface area found in the placentae of diabetic mothers can be enlarged very significantly by the microvilli, in terms of the total trophoblastic surface area which is in contact with the maternal blood. On a functional basis, these findings support the theory that placental function is probably not adversely affected in these placentae, and that these placentae can efficiently support the growth of large fetuses.

Female↗
PubMed1981

Genes, individuals, and kin selection.

The altruistic-gene theory of kin selection requires conditions so improbable that its reality is doubtful. The gene-quantity theory, including the theory of inclusive fitness, assumes that selection acts on sums of kins' genes, but no effective mechanism is apparent. Insect and human societies may have evolved by individual selection, in two steps: first something made staying together advantageous to individuals, and then altruistic behaviors evolved in net-gain lotteries, also (statistically) advantageous to individuals. Kin selection is not required in these or any other unequivocal cases; the theory should be reexamined and probably abandoned. The probability of kin selection is further reduced by the cost of evolution by selection. Much current evolutionary mathematics and determinist sociobiology, which ignore how the cost of selection limits the precision of adaptations, including adaptive behaviors, may be dangerously unrealistic.

Journal Article↗
PubMed2002

Common processes may contribute to extinction and habituation.

Psychologists routinely attribute the characteristics of conditioned behavior to complicated cognitive processes. For example, many of the characteristics of behavior undergoing extinction have been attributed to retrieval from memory. The authors argue that these characteristics may result from the simpler process of habituation. In particular, conditioned responding may decrease during extinction partially because habituation occurs to the stimuli that control responding when those stimuli are presented repeatedly or for a prolonged time (e.g., the experimental context, the conditioned stimulus in classical conditioning). This idea is parsimonious, has face validity, and evokes only processes that are well established by other evidence. In addition, behavior undergoing extinction shows 12 of the fundamental properties of behavior undergoing habituation. However, this model probably cannot provide a complete theory of extinction. It provides no obvious explanation for some of the other characteristics of extinguished behavior.

Animals↗