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At least 613 records · Page 34Linked to original sources
PubMed1998

Detection of global structure in Glass patterns: implications for form vision.

Glass (Nature 1969;223:578-580) patterns are random dot stimuli that generate a percept of global structure. To study the mechanisms underlying this global form perception, concentric, radial, hyperbolic, and parallel Glass patterns were constructed. Thresholds for detecting each type of pattern were measured by degrading the patterns through the addition of noise. Concentric patterns yielded the lowest thresholds for all subjects, while radial and hyperbolic patterns produced somewhat higher thresholds. For all subjects the parallel patterns produced the highest thresholds. Threshold measurements as a function of the area containing pattern structure provided evidence for global pooling of orientation information in the detection of radial and concentric Glass patterns but only local pooling in the detection of parallel patterns. Monte-Carlo simulations demonstrate that plausible neural models can accurately predict the data. These models indicate that the visual system contains networks that pool orientation information within regions 3.5-4.5 degrees in diameter in central vision. This pooling is organized to extract cross-shaped, X-shaped, and quasi-circular forms from the retinal image. The results are in good agreement with recent single unit physiology of primate area V4, an intermediate level of the form vision pathway.

Computer Graphics↗
PubMed2004

Photogenerated polyelectrolyte bilayers from an aqueous-processible photoresist for multicomponent protein patterning.

A novel photoresist (PR) that can be processed under mild aqueous conditions was synthesized and used to create photogenerated polyelectrolyte bilayers. Thin films of the PR cast on polycation-coated substrates were exposed to UV irradiation to generate carboxylate groups in the photoresist. The bulk of the UV-exposed PR film was dissolved by rinsing with pH 7.4 phosphate-buffered saline, but a polyelectrolyte bilayer formed in situ at the PR/polycation interface on exposure remained bound to the substrate. The UV-exposed photoresist also exhibited pH-dependent solubility; it was soluble in water above pH 6.6, but insoluble at lower pHs. Using these unique properties, two-component protein patterning was achieved using biotinylated PR films under conditions that avoid exposing the proteins to conditions outside the narrow range of physiological pH, ionic strength, and temperature where their stability is greatest.

Biotin↗
PubMed1991

Differential induction of interferon gamma gene expression after activation of CD4+ T cells by conventional antigen and Mls superantigen.

We have analyzed cytokine gene expression by a murine CD4+ T-cell clone that expresses three forms of T-cell recognition. The clone employs a V beta 6-containing T-cell receptor to recognize (i) a self class II major histocompatibility complex and an ovalbumin-derived peptide (OVA), (ii) an I-Ab alloantigen, and (iii) Mls-1a. All three responses are accompanied by similar levels of cell proliferation. However, although interferon gamma gene expression is strongly induced during both physiological recognition of the OVA peptide and allogeneic major histocompatibility complex recognition, expression of this gene was not detected during the Mls response. These studies indicate that Mls recognition is functionally distinct from T-cell recognition of peptides and alloantigens and leads to an alternative pattern of cytokine gene expression. They also suggest the possibility that encounter with these two classes of T-cell antigen in vivo may generate subsets of T helper cells that display different patterns of cytokine gene expression.

Animals↗
PubMed2005

Extraction of biological interaction networks from scientific literature.

Biology can be regarded as a science of networks: interactions between various biological entities (eg genes, proteins, metabolites) on different levels (eg gene regulation, cell signalling) can be represented as graphs and, thus, analysis of such networks might shed new light on the function of biological systems. Such biological networks can be obtained from different sources. The extraction of networks from text is an important technique that requires the integration of several different computational disciplines. This paper summarises the most important steps in network extraction and reviews common approaches and solutions for the extraction of biological networks from scientific literature.

Abstracting and Indexing↗
PubMed2004

Neural correlates of change detection and change blindness in a working memory task.

Detecting changes in an ever-changing environment is highly advantageous, and this ability may be critical for survival. In the present study, we investigated the neural substrates of change detection in the context of a visual working memory task. Subjects maintained a sample visual stimulus in short-term memory for 6 s, and were asked to indicate whether a subsequent, test stimulus matched or did not match the original sample. To study change detection largely uncontaminated by attentional state, we compared correct change and correct no-change trials at test. Our results revealed that correctly detecting a change was associated with activation of a network comprising parietal and frontal brain regions, as well as activation of the pulvinar, cerebellum, and inferior temporal gyrus. Moreover, incorrectly reporting a change when none occurred led to a very similar pattern of activations. Finally, few regions were differentially activated by trials in which a change occurred but subjects failed to detect it (change blindness). Thus, brain activation was correlated with a subject's report of a change, instead of correlated with the physical change per se. We propose that frontal and parietal regions, possibly assisted by the cerebellum and the pulvinar, might be involved in controlling the deployment of attention to the location of a change, thereby allowing further processing of the visual stimulus. Visual processing areas, such as the inferior temporal gyrus, may be the recipients of top-down feedback from fronto-parietal regions that control the reactive deployment of attention, and thus exhibit increased activation when a change is reported (irrespective of whether it occurred or not). Whereas reporting that a change occurred, be it correctly or incorrectly, was associated with strong activation in fronto-parietal sites, change blindness appears to involve very limited territories.

Adaptation, Physiological↗
PubMed2004

Enhanced temporal non-linearities in human object-related occipito-temporal cortex.

To what extent does neural activation in human visual cortex follow the temporal dynamics of the optical retinal stimulus? Specifically, to what extent does stimulus evoked neural activation persist after stimulus termination? In the present study, we used functional magnetic resonance imaging (fMRI) to explore the resulting temporal non-linearities across the entire constellation of human visual areas. Gray-scale images of animals, houses and faces were presented at two different presentation rates - 1 and 4 Hz - and the fMRI signal was analyzed in retinotopic and in high order occipito-temporal visual areas. In early visual areas and the motion sensitive area MT/V5, a fourfold increase in stimulus presentation rate evoked a twofold increase in signal amplitude. However, in high order visual areas, signal amplitude increased only by 25%. A control experiment ruled out the possibility that this difference was due to signal saturation ('ceiling') effects. A likely explanation for the stronger non-linearities in occipito-temporal cortex is a persistent neuronal activation that continues well after stimulus termination in the 1 Hz condition. These persistent activations might serve as a short term (iconic) memory mechanism for preserving a trace of the stimulus even in its absence and for future integration with temporally correlated stimuli. Two alternative models of persistence (inhibitory and excitatory) are proposed to explain the data.

Adaptation, Physiological↗
PubMed2000

Searching genomes for sequences with the potential to form intrastrand triple helices.

The canonical double-helix form of DNA is thought to predominate both in dilute solution and in living cells. Sequence-dependent fluctuations in local DNA shape occur within the double helix. Besides these relatively modest variations in shape, more extreme and remarkable structures have been detected in which some bases become unpaired. Examples include unusual three-stranded structures such as H-DNA. Certain RNA and DNA strands can also fold onto themselves to form intrastrand triplexes. Although they have been extensively studied in vitro, it remains unknown whether nucleic acid triplexes play natural roles in cells. If natural nucleic acid triplexes were identified in cells, much could be learned by examining the formation, stabilization, and function of such structures. With these goals in mind, we adapted a pattern-recognition program to search genetic databases for a type of potential triplex structure whose presence in genomes has not been previously investigated. We term these sequences Potential Intrastrand Triplex (PIT) elements. The formation of an intrastrand triplex requires three consecutive sequence domains with appropriate symmetry along a single nucleic acid strand. It is remarkable that we discovered multiple copies of sequence elements with the potential to form one particular class of intrastrand triplexes in the fully sequenced genomes of several bacteria. We then focused on the characterization of the 25 copies of a particular approximately 37 nt PIT sequence detected in Escherichia coli. Through biochemical studies, we demonstrate that an isolated DNA strand from this family of E. coli PIT elements forms a stable intrastrand triplex at physiological temperature and pH in the presence of physiological concentrations of Mg(2+).

Algorithms↗
PubMed2005

gammadelta T cells link innate and adaptive immune responses.

While most T cells use a CD3-associated alpha/beta T cell receptor as antigen recognition structure, a second population of T cells expresses the alternative gamma/delta T cell receptor. gamma/delta T cells are a minor population in the peripheral blood but constitute a major population among intestinal intraepithelial lymphocytes. Most gamma/delta T cells recognize ligands which are fundamentally different from the short peptides that are seen by alpha/beta T cells in the context of MHC class I or class II molecules. Thus, human Vdelta2 T cells recognize small bacterial phosphoantigens, alkylamines and synthetic aminobisphosphonates, whereas Vdelta1 T cells recognize stress-inducible MHC-related molecules MICA/B as well as several other ligands. At the functional level, gamma/delta T cells rapidly produce a variety of cytokines and usually exert potent cytotoxic activity, also towards many tumor cells. In this article, we discuss the role of gamma/delta T cells as a bridge between the innate and the adaptive immune system, based on the interpretation that gamma/delta T cells use their T cell receptor as a pattern recognition receptor. Our increasing understanding of the ligand recognition and activation mechanisms of gamma/delta T cells also opens new perspectives for the development of gamma/delta T cell-based immunotherapies.

Adaptation, Physiological↗
PubMed1993

Visual modelling.

The first purpose of this paper is to present a neural net model of the visual cortex of higher vertebrates based on the electrophysiological properties of the ganglion cells. This model takes Hebb's law [1] as the physiological learning rule for synaptic modification. The model consists of 85 x 85 neurons forming a layer similar to the cortex. The neurones are massively connected via weights that are typically adapted. We simulate several input patterns and show that the model reproduces the pattern recognition, contours pictures and moving perception.

Algorithms↗
PubMed1987

CAMs and Igs: cell adhesion and the evolutionary origins of immunity.

The lymphoid system and cells of immunity are as morphologically well defined as those of any complex organ but in addition they show dynamic long-range interactions between the fluid tissues (lymphocytes, monocytes, etc.) and the solid, vascular and generative tissues and organs which they comprise. Given the observation that CAMs are present in epithelial components of lymphoid organs, it appears that, in their ontogeny, the organs of immunity will share a common principle of morphoregulation by CAMs with brains, feathers and other parts of the phenotype. As discussed here, this principle is a regulatory one operating across many levels of organization from the genes to tissues and back again (see Fig. 1). At some early point in the evolution of the immune system, a gene corresponding to an N-CAM precursor must have duplicated to provide a basis for the Ig superfamily with its increasing specializations for recognition and for cellular regulation during the immune response. Lymphocyte cellular families also developed later specializations (along with other leukocytes) for adhesive functions accessory to specific recognition. As far as we can see, the molecules for these accessory functions only remotely resemble CAMs, but closely resemble receptors for matrix molecules and SAMs. What CAMs and Ig superfamily members have in common is an evolutionary path and important roles in mediating complex regulatory responses that arise from cell-cell interactions. In the one case, this regulation leads to morphology, and in the other, to immune recognition. The first depends directly upon pattern (the formation of definite tissue structure); the regulation of the second also depends upon pattern to the extent that its function is dependent upon the morphology of lymphoid organs and vasculature. But although specific immune recognition depends locally upon adhesion through special mechanisms, it does not lead to morphology. One must not therefore impute too much in the physiological sense to the resemblance among brain molecules and molecules of the immune system. CAMs themselves are not directly histotypic at the level of individual differentiated cells but rather are used to link early tissue boundaries in induction and function in a wide variety of different tissues. As a consequence, N-CAM is central to the formation and maintenance of neural tissue but has a much wider tissue distribution and a fundamental role in very early embryogenesis as is the case with other primary CAMs. Thus, the immune system did not evolve from the nervous system, but from a cell adhesion system essential to both.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2005

Behavioral and psychiatric consequences of sleep-wake schedule disorders.

Circadian rhythm sleep disorders (CRSDs) arise when an individual's sleep-wake rhythm mismatches the environmental 24-h schedule. Physiological data and genetic studies in patients with CRSDs suggest that these disorders result from abnormal functioning of the circadian timing system. Diagnosis involves recognition of the characteristics of CRSDs, which can be achieved by clinical interview and actigraphic monitoring of rest-activity patterns. Bright-light therapy and melatonin administration have proved to be the most effective treatment modalities of CRSDs. In psychiatric practice, CRSDs can be encountered on various occasions. Some evidence indicates that a deviant sleep-wake schedule might be a predisposing factor to personality disorders. CRSDs can emerge as an iatrogenic effect of certain psychoactive drugs, such as haloperidol and fluvoxamine. It is not uncommon that the daytime functional difficulties that accompany CRSDs are misinterpreted as symptoms of psychopathology. Recognition and awareness of these disorders should prevent years of erroneous diagnosis and treatment in these patients.

Circadian Rhythm↗
PubMed2001

Gain modulation in the central nervous system: where behavior, neurophysiology, and computation meet.

Gain modulation is a nonlinear way in which neurons combine information from two (or more) sources, which may be of sensory, motor, or cognitive origin. Gain modulation is revealed when one input, the modulatory one, affects the gain or the sensitivity of the neuron to the other input, without modifying its selectivity or receptive field properties. This type of modulatory interaction is important for two reasons. First, it is an extremely widespread integration mechanism; it is found in a plethora of cortical areas and in some subcortical structures as well, and as a consequence it seems to play an important role in a striking variety of functions, including eye and limb movements, navigation, spatial perception, attentional processing, and object recognition. Second, there is a theoretical foundation indicating that gain-modulated neurons may serve as a basis for a general class of computations, namely, coordinate transformations and the generation of invariant responses, which indeed may underlie all the brain functions just mentioned. This article describes the relationships between computational models, the physiological properties of a variety of gain-modulated neurons, and some of the behavioral consequences of damage to gain-modulated neural representations.

Animals↗
PubMed1997

Pupil response triggered by the onset of coherent motion.

BACKGROUND: Recent studies have shown that transient constrictions of the pupil can be elicited by visual stimuli that do not cause an increment in light flux level on the retina. Such stimuli include achromatic gratings and isoluminant chromatic patterns. METHOD: We investigated pupillary responses to the onset of coherent movement generated in a pattern of dots in random motion. Measurements were carried out in normal observers and in a subject with hemianopia caused by damaged primary visual cortex. RESULTS: The experimental findings show that the onset of coherent motion triggers systematic constrictions of the pupil that cannot be accounted for in terms of a pupil light reflex response. We labelled these constrictions Pupil motion responses (PMRs). Results show that PMRs have large response latencies and on average are of small response amplitudes. The dependence of PMRs on changes in motion parameters such as stimulus speed and direction of motion has been investigated. CONCLUSIONS: The existence of PMRs to the onset of the coherent motion in human vision has been demonstrated. These new findings are discussed in relation to the psychophysical and physiological data on motion perception and the possible pathways involved in the control of the pupil response.

Hemianopsia↗
PubMed2006

Reading embossed capital letters: an fMRI study in blind and sighted individuals.

Reading Braille activates visual cortex in blind people [Burton et al., J Neurophysiol 2002;87:589-611; Sadato et al., Nature 1996;380:526-528; Sadato et al., Brain 1998;121:1213-1229]. Because learning Braille requires extensive training, we had sighted and blind people read raised block capital letters to determine whether all groups engage visual cortex similarly when reading by touch. Letters were passively rubbed across the right index finger at 30 mm/s using an MR-compatible drum stimulator. Age-matched sighted, early blind (lost sight 0-5 years), and late blind (lost sight >5.5 years) volunteers performed three tasks: stating an identified letter, stating a verb containing an identified letter, and feeling a moving smooth surface. Responses were voiced immediately after the drum stopped moving across the fingertip. All groups showed increased activity in visual areas V1 and V2 during both letter identification tasks. Blind compared to sighted participants showed greater activation increases predominantly in the parafoveal-peripheral portions of visuotopic areas and posterior parts of BA 20 and 37. Sighted participants showed suppressed activity in most of the same areas except for small positive responses bilaterally in V1, left V5/MT+, and bilaterally in BA 37/20. Blind individuals showed suppression of the language areas in the frontal cortex, while sighted individuals showed slight positive responses. Early blind showed a more extensive distribution of activity in superior temporal sulcal multisensory areas. These results show cross-modal reorganization of visual cortex and altered response dynamics in nonvisual areas that plausibly reflect mechanisms for adaptive plasticity in blindness.

Adaptation, Physiological↗
PubMed2006

Prefrontal cell activities related to monkeys' success and failure in adapting to rule changes in a Wisconsin Card Sorting Test analog.

The cognitive flexibility to select appropriate rules in a changing environment is essential for survival and is assumed to depend on the integrity of prefrontal cortex (PFC). To explore the contribution of the dorsolateral PFC to flexible rule-based behavior, we recorded the activity of cells in this region of monkeys performing a Wisconsin Card Sorting Test (WCST) analog. The monkey had to match a sample to one of three test items by either color or shape. Liquid reward and a discrete visual signal (error signal) were given as feedback to correct and incorrect target selections, respectively. The relevant rule and its frequent changes were not cued, and the monkeys could find it only by interpreting the feedback. In one-third of cells, cellular activity was modulated by the relevant rule, both throughout the trial and between trials. The magnitude of the modulation correlated with the number of errors that the monkeys committed after each rule change in the course of reestablishing high performance. Activity of other cells differed between correct and error trials independently from the rule-related modulation. This difference appeared during actual responses and before the monkeys faced the problems. Many PFC cells responded to the error-signal presentation, and, in some of them, the magnitude of response depended on the relevant rule. These results suggest that the dorsolateral PFC contributes to WCST performance by maintaining the relevant rule across trials, assessing behavioral outcomes, and monitoring the processes that could lead to success and failure in individual trials.

Action Potentials↗
PubMed1976

Culture, adaptation, and patterns of disease.

The sick patient, rather than the disease process itself, should occupy the central focus of the physician's attention. Such an approach recognizes the interaction of physiologic and emotional forces in the occurrence of disease. It allows for a consideration of the contributory role of emotions in the precipition of physical illness and a recognition that physical illness may produce emotional sequelae of relevance to the total clinical problem. It is an approach which views man as an adapting animal, whose environment may play a crucial role in his adaptation and his disease. Only with such a perspective of man and disease can the principles of medical treatment be realistic.

Abortion, Induced↗