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PubMed2003

Human temporal impulse response speeds up with increased stimulus contrast.

It is well known that raising mean luminance speeds-up the visual response to temporal change. At higher mean luminance, the temporal impulse response function (IRF) becomes more transient or biphasic. An analogous effect is observed physiologically when stimulus contrast is increased, at constant mean luminance. As stimulus contrast is raised, the temporal response to flicker advances in phase and becomes more transient (bandpass). The MC (magnocellular) retinal ganglion cells manifest this temporal contrast gain control, but the PC (parvocellular) cells do not. We show psychophysically that the temporal response in humans speeds-up in an analogous manner as stimulus contrast is raised. Low spatial-frequency gratings, of suprathreshold contrast, were presented as pairs of pulses, separated by brief delays. Responses became more transient with increasing contrast in both our motion task (direction discrimination) and in our flicker task ('agitation' discrimination), mimicking the temporal contrast gain control seen in the physiological studies. Results could be modeled with a nonlinearity, in which the IRF shortens with increasing contrast.

Contrast Sensitivity↗
PubMed1998

The role of "contrast enhancement" in the detection and appearance of visual contours.

We test the proposition that the appearance and detection of visual contours is based on an increase in the perceived contrast of contour elements. First we show that detection of contours is quite possible in the presence of very high levels of variability in contrast. Second we show that inclusion in a contour does not induce Gabor patches to appear to be of higher contrast than patches outside of a contour. These results suggest that, contrary to a number of current models, contrast or its assumed physiological correlate (the mean firing rate of early cortical neurons) is not the determining information for identifying the contour.

Contrast Sensitivity↗
PubMed2006

A gain-control theory of binocular combination.

In binocular combination, light images on the two retinas are combined to form a single "cyclopean" perceptual image, in contrast to binocular rivalry which occurs when the two eyes have incompatible ("rivalrous") inputs and only one eye;s stimulus is perceived. We propose a computational theory for binocular combination with two basic principles of interaction: in every spatial neighborhood, each eye (i) exerts gain control on the other eye's signal in proportion to the contrast energy of its own input and (ii) additionally exerts gain control on the other eye's gain control. For stimuli of ordinary contrast, when either eye is stimulated alone, the predicted cyclopean image is the same as when both eyes are stimulated equally, coinciding with an easily observed property of natural vision. The gain-control theory is contrast dependent: Very low-contrast stimuli to the left- and right-eye add linearly to form the predicted cyclopean image. The intrinsic nonlinearity manifests itself only as contrast increases. To test the theory more precisely, a horizontal sine wave grating of 0.68 cycles per degree is presented to each eye. The gratings differ in contrast and phase. The predicted (and perceived) cyclopean grating also is a sine wave; its apparent phase indicates the relative contribution of the two eyes to the cyclopean image. For 48 measured combinations of phase and contrast, the theory with only one estimated parameter accounts for 95% of the variance of the data. Therefore, a simple, robust, physiologically plausible gain-control theory accurately describes an early stage of binocular combination.

Contrast Sensitivity↗
PubMed2005

Metabolomics: from pattern recognition to biological interpretation.

Metabolomics is a technology that aims to identify and quantify the metabolome -- the dynamic set of all small molecules present in an organism or a biological sample. In this sense, the technique is distinct from metabolic profiling, which looks for target compounds and their biochemical transformation. The combination of both approaches is an emerging technique for the characterization of biological samples and for drug treatment. Metabolomics has proven to be very rapid and superior to any other post-genomics technology for pattern-recognition analyses of biological samples. Changing steady state concentrations and fluctuations of metabolites that occur within milliseconds are a result of biochemical processes such as signalling cascades: metabolomic techniques are instrumental in measuring these changes rapidly and sensitively. Metabolite data can be complemented by protein, transcript and external (environmental) data, thereby leading to the identification of multiple physiological biomarkers embedded in correlative molecular networks that are not approachable with targeted studies.

Biomarkers↗
PubMedDate not supplied

The emerging functionality of endogenous lectins: A primer to the concept and a case study on galectins including medical implications.

Biochemistry textbooks commonly make it appear that it is a foregone conclusion that the hardware of biological information storage and transfer is confined to nucleotides and amino acids, the letters of the genetic code. However, the remarkable talents of a third class of biomolecules are often overlooked. For example, one of them far surpasses the building blocks of nucleic acids and proteins in terms of theoretical coding capacity by oligomer formation. Although often exclusively assigned to duties in energy metabolism, carbohydrates as part of cellular glycoconjugates (glycoproteins, proteoglycans, glycolipids) have, in fact, other important tasks. Currently, they are increasingly gaining recognition as an operative high-density information coding system. An elaborate enzymatic machinery enables cells to be versatile enough to produce a glycan profile (glycome) that is as characteristic as a fingerprint. Moreover, swift modifications during dynamic processes, such as differentiation or malignant transformation, are readily possible. The translation of the information presented in oligosaccharide determinants to biological responses is carried out by lectins. Recognition of foreign glycosignatures in innate immunity, regulation of cell-cell/matrix interactions, cell migration or growth, and intra- and intercellular glycan routing etc represent physiologically far-reaching lectin-carbohydrate functionality. The classification of endogenous lectins is guided by sequence alignments and conservation of distinct structural traits. For example, a jelly-roll-like folding pattern and maintenance of key residue positioning involved in stacking and C-H/pi-interactions as well as directional hydrogen bonds to the 1-galactoside ligands are common denominators among galectins. Biochemical and biophysical studies are beginning to unravel the intricacies of the selection of a limited set of endogenous ligands, such as certain integrins or ganglioside GM1, and combined with biological cell experiments, its relevance for cell sociology, e.g. in growth regulation and tumor cell invasion or activated T cell apoptosis. Histopathological monitoring accompanies the biological cell investigations, linking expression of certain family members to tumor progression or suppression. Further insights into the functional consequences of the sugar code's translation are thus expected to have notable repercussions for diagnostic and therapeutic procedures.

Amino Acid Sequence↗
PubMedDate not supplied

Prevention of psychological disability after occupational respiratory exposures.

"Psychological injury" in the workplace constitutes the fastest-growing sector of workers' compensation disability claims in several states. Most such claims pertain to effects of "occupational stress," including interpersonal conflicts with supervisors or co-workers, adaptation to changing work practices, and job insecurity. Of equal interest are the psychological consequences of chemical insults on the job. In the case of occupational respiratory exposures, psychological co-morbidity may occur along with a variety of acute, chronic, and latent illness states. Both predictable responses (such as adjustment reactions to disabling physical conditions) and idiopathic patterns (such as the development of odor-conditioned panic attacks or panic disorder) have been described. Physicians who evaluate and treat such patients need to be alert to the potential interaction of physiological and psychological stressors. Effective prevention and treatment requires not only an appreciation of the patient's view of the disease process, but also a recognition of the role of prognostic uncertainty in the subsequent development of anxiety symptoms. In some cases, exclusive attention to physical signs and symptoms may actually lead to a worsening of impairment and disability.

Adaptation, Psychological↗
PubMed2003

Cognition and aging: a highly selective overview of event-related potential (ERP) data.

An overview of highly selected cognitive aging investigations of deviance detection, episodic memory and working memory reveals two primary themes: (1) when variability in elderly samples has been assessed, it has proven useful in understanding age-related changes in cognition; and (2) there is a frontal lobe contribution to at least some age-related changes in cognition. However, there are too few ERP age-related investigations of individual differences to determine whether the changes in patterns of ERP responding can be deemed "compensatory" or "inefficient." It is suggested that, to the extent possible, future electrophysiological investigations of cognitive aging (as well as other physiological measurement techniques) include individual difference measures that will enable the determination of the implication of a given neural pattern in the genesis of a given, age-related behavioral outcome pattern.

Adolescent↗
PubMed1999

Amplification of the antibody response by C3b complexed to antigen through an ester link.

Complement C3 has been described as playing an important role in the cell-mediated immune response. C3b has the capacity to covalently bind Ag and then to stimulate in vitro Ag presentation to T lymphocytes. To verify this observation in vivo, we prepared and purified covalent human C3b-Ag complexes using lysozyme (HEL) as Ag. The characterization of these HEL-C3b complexes indicates that they are representative of those susceptible to be generated in physiological conditions. Mice were immunized with 0.1 to 0.6 microgram of either free HEL, HEL + C3b, HEL-C3b, or HEL + CFA. Response was assessed after two i.p. injections by quantification of specific Ab production. Immunization with either HEL-C3b complexes or HEL + CFA leads to anti-HEL IgG production whereas free HEL or HEL + C3b was ineffective. Either HEL-C3b or HEL + CFA immunizations led to a similar Ig subclass patterns, including IgG1, IgG2a, IgA, and IgM. Our experiments provide the first evidence for modulation of specific Ab response by C3b when it is bound to Ag through a physiological-like link. Taken together with previous data concerning Ab response following recombinant HEL-C3d immunization, cellular events such as processing of C3b-Ag by APC and recognition by T lymphocytes, this present result underlines the importance of C3b and its fragments in stimulation of the immune system, through the multiplicity and complementarity of its interactions.

Animals↗
PubMed1983

The brain as a geometer.

The fragmentary cues we have on the geometric aptitudes of the brain (e.g., in evaluating shapes or appreciating depth) do not lead to a unified model of perceptual geometry. In parallel with physiological studies, aimed at explaining how perception works, I suggest developing the study of the geometrical capabilities of the brain, in order to learn precisely what is accomplished.

Brain↗
PubMed2006

Pupillometry of grapheme-color synaesthesia.

Pupil diameters of color-grapheme synaesthetes were measured with an infrared eye-tracker while Stroop-like alphanumeric symbols were passively viewed. Pupils dilated more when synaesthetes viewed incongruently-colored symbols than congruently-colored symbols or symbols printed in the standard black ink. The results show that the physiological measure of pupillary diameter can be used as a marker of the synaesthetic experience.

Adult↗
PubMed2002

Learning the invariance properties of complex cells from their responses to natural stimuli.

Neurons in primary visual cortex are typically classified as either simple or complex. Whereas simple cells respond strongly to grating and bar stimuli displayed at a certain phase and visual field location, complex cell responses are insensitive to small translations of the stimulus within the receptive field [Hubel & Wiesel (1962) J. Physiol. (Lond.), 160, 106-154; Kjaer et al. (1997) J. Neurophysiol., 78, 3187-3197]. This constancy in the response to variations of the stimuli is commonly called invariance. Hubel and Wiesel's classical model of the primary visual cortex proposes a connectivity scheme which successfully describes simple and complex cell response properties. However, the question as to how this connectivity arises during normal development is left open. Based on their work and inspired by recent physiological findings we suggest a network model capable of learning from natural stimuli and developing receptive field properties which match those of cortical simple and complex cells. Stimuli are drawn from videos obtained by a camera mounted to a cat's head, so they should approximate the natural input to the cat's visual system. The network uses a competitive scheme to learn simple and complex cell response properties. Employing delayed signals to learn connections between simple and complex cells enables the model to utilize temporal properties of the input. We show that the temporal structure of the input gives rise to the emergence and refinement of complex cell receptive fields, whereas removing temporal continuity prevents this processes. This model lends a physiologically based explanation of the development of complex cell invariance response properties.

Animals↗
PubMed1990

Asymmetrical brain electrical activity discriminates between psychometrically-matched verbal and spatial cognitive tasks.

This study compared the asymmetry of different features of brain electrical activity during the performance of a verbal task (word finding) and a spatial task (dot localization) that had been carefully matched on psychometric properties and accompanying motor activity. Nineteen right-handed subjects were tested. EEG was recorded from F3, F4, C3, C4, P3, and P4, referred to both CZ and computer-derived averaged-ears references, and Fourier transformed. Power in the delta, theta, alpha, and beta bands was computed. There were significant Task X Hemisphere effects in all bands for CZ-referenced data and for the alpha and beta bands for ears-referenced data. The effects were always either greater power suppression in the hemisphere putatively most engaged in task processing or greater power in the opposite hemisphere. Correlations between EEG and task performance indicated that CZ-referenced parietal alpha asymmetry accounted for the most variance in verbal task performance. Power within individual hemispheres or across hemispheres was unrelated to task performance. The findings indicate robust differences in asymmetrical brain physiology that are produced by well-matched verbal and spatial cognitive tasks.

Adult↗
PubMed1990

[Plasticity of the callosal system].

A series of experiments examined the potential plasticity of the callosal system in both epileptic patients and in kittens submitted to corpus callosotomy at various ages. The patients were tested for unilateral discrimination and interhemispheric transfer of tactile information. The youngest patient was also required to perform additional inter- and intrahemispheric comparisons of visual and tactile stimuli. The animals were tested for interhemispheric transfer of visual discriminations. The results suggest that in both animals and humans there exists a critical period before which callosal section does not disrupt interhemispheric communication. The results also indicate that the compensatory mechanisms used to achieve interhemispheric transfer in the absence of the corpus callosum may vary according to the sensory modality involved. The possible physiological and/or functional mechanisms responsible for callosal plasticity are discussed.

Adolescent↗
PubMed2005

Cognitive performance in relation to vitamin status in healthy elderly German women-the effect of 6-month multivitamin supplementation.

BACKGROUND: Prior investigations have reported a link between poor status of antioxidants, folate, and cobalamin resulting in elevated total plasma homocysteine (tHcy) and methylmalonic acid (MMA) concentrations with an increased risk for reduced cognitive performance. The aim of the study was to evaluate the effect of a 6-month multivitamin supplementation on the cognitive performance of female seniors and to assess cognitive functioning in relation to vitamin status, tHcy, and MMA values at baseline. METHODS: The study was performed as a randomized placebo-controlled double-blind trial. 220 healthy, free-living women (aged 60-91 years) were included. Blood drawings and cognitive tests were performed at the Institute of Food Science of the University of Hanover, Germany. Vitamin and cognitive status have been evaluated prior to and 6 months after supplementation. Plasma ascorbic acid, serum concentrations of alpha-tocopherol, beta-carotene, and coenzyme Q10, serum and erythrocyte folate as well as serum cobalamin, serum MMA, and plasma tHcy concentrations were measured. Activity coefficient of erythrocyte alpha aspartic aminotransferase was used as functional index for vitamin B(6) status. The cognitive performance was assessed by the Symbol Search test, a subtest of the Wechsler Adult Intelligence Scale (WAIS-III) and the pattern-recognition test. Intelligence as assessed by the 'Kurztest für Allgemeine Intelligenz' (KAI) was a further variable. RESULTS: No significant differences in pattern-recognition and intelligence score were observed between vitamin and placebo group prior to and after multivitamin supplementation. In the Symbol Search test, the vitamin group exhibited better test results than the placebo group at both measure points. One-way ANOVA showed a marginally significant linear trend between the baseline tHcy concentration and the pattern-recognition score (P = 0.051) in the total sample. Multiple backward regression revealed only a significant influence of the school graduation on baseline cognitive function test results. A general linear model showed that the changes in cognitive function scores could not be explained by the type of treatment or blood parameters. CONCLUSIONS: Our data indicate that 6 months supplementation of physiological dosages of antioxidants and B vitamins have no effect on cognitive performance in presumedly healthy and well-nourished female seniors. An intervention period of only 6 months may be too short for improving cognitive performance in well-educated elderly women without dementia.

Aged↗
PubMed1997

Isolation and characterization of a new member of the scavenger receptor superfamily, glycoprotein-340 (gp-340), as a lung surfactant protein-D binding molecule.

We have purified a previously unknown glycoprotein (designated gp-340) from human bronchioalveolar lung washings from a patient with alveolar proteinosis. gp-340 was identified by its calcium-dependent binding to lung surfactant protein D (SP-D) and by its molecular mass of 340 kDa in the reduced state on SDS-polyacrylamide gel electrophoresis (PAGE). gp-340 was purified from the 10,000 x g pellet of the lavage fluid by ion-exchange and gel permeation chromatography. On SDS-PAGE, gp-340 showed an apparent molecular mass of 290 kDa in the unreduced state. On gel chromatography under non-dissociating conditions, the apparent molecular mass of gp-340 was >1000 kDa. The presence of N-linked glycosylation was shown by digestion with N-glycosidase F, which reduced the apparent molecular mass of gp-340 under reducing condition to about 300 kDa. Partial amino acid sequence data showed the presence of scavenger-receptor type domains. Monoclonal and polyclonal antibodies were raised against gp-340, and their specificities were confirmed by Western blotting. The antibodies were used for immunohistochemical localization of gp-340 in the lung, where it was found on the surface of and within alveolar macrophages. Direct binding between gp-340 and SP-D took place at physiological ionic strength, required the presence of calcium, and was not inhibited by maltose. The binding between SP-D and mannan also required the presence of calcium, but this interaction was completely inhibited by maltose. The same binding pattern was seen between gp-340 and recombinant human SP-D composed of the trimeric neck region and three carbohydrate recognition domains. These findings indicate that the binding between gp-340 and SP-D is a protein-protein interaction rather than a lectin-carbohydrate interaction and that the binding to gp-340 takes place via the carbohydrate recognition domain of SP-D. We conclude that gp-340 is a new member of the scavenger-receptor superfamily and likely to be a truncated form of a receptor for SP-D.

Amino Acid Sequence↗
PubMed1999

Inhibition of L-selectin-mediated leukocyte rolling by synthetic glycoprotein mimics.

Synthetic carbohydrate and glycoprotein mimics displaying sulfated saccharide residues have been assayed for their L-selectin inhibitory properties under static and flow conditions. Polymers displaying the L-selectin recognition epitopes 3',6-disulfo Lewis x(Glc) (3-O-SO3-Galbeta1alpha4(Fucalpha1alpha3)-6-O-SO3-Glcbeta+ ++-OR) and 3',6'-disulfo Lewis x(Glc) (3, 6-di-O-SO3-Galbeta1alpha4(Fucalpha1alpha3)Glcbeta-OR) both inhibit L-selectin binding to heparin under static, cell-free binding conditions with similar efficacies. Under conditions of shear flow, however, only the polymer displaying 3',6-disulfo Lewis x(Glc) inhibits the rolling of L-selectin-transfected cells on the glycoprotein ligand GlyCAM-1. Although it has been shown to more effective than sialyl Lewis x at blocking the L-selectin-GlyCAM-1 interaction in static binding studies, the corresponding monomer had no effect in the dynamic assay. These data indicate that multivalent ligands are far more effective inhibitors of L-selectin-mediated rolling than their monovalent counterparts and that the inhibitory activities are dependent on the specific sulfation pattern of the recognition epitope. Importantly, our results indicate the L-selectin specificity for one ligand over another found in static, cell-free binding assays is not necessarily retained under the conditions of shear flow. The results suggest that monovalent or polyvalent carbohydrate or glycoprotein mimetics that inhibit selectin binding in static assays may not block the more physiologically relevant process of selectin-mediated rolling.

Animals↗
PubMed2004

Recent research findings on aggressive and violent behavior in youth: implications for clinical assessment and intervention.

Assessing children and adolescents for potential violent behavior requires an organized approach that draws on clinical knowledge, a thorough diagnostic interview, and familiarity with relevant risk and protective factors. This article reviews empirical evidence on risk factors, the impact of peers, developmental pathways, physiological markers, subtyping of aggression, and differences in patterns of risk behaviors between sexes. We explore these determinants of violence in children and adolescents with attention to the underlying motivations and etiology of violence to delineate the complexity, unanswered questions, and clinical relevance of the current research. Interventions, including cognitive behavioral therapy, psychopharmacological treatment, and psychosocial treatment, are reviewed with acute recognition of the need to use multiple modalities with, and to expand research to define optimal treatment for, potentially violent children and adolescents. The information considered for this review focuses on violence as defined as physical aggression toward other individuals. Other studies are included with wider definitions of violence because of their relevance to assessing the potential for violent behavior.

Adolescent↗