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At least 415 records · Page 23Linked to original sources
PubMed2001

Directional tuning of human motion adaptation as reflected by the motion VEP.

Motion onset evoked visual potentials are dominated by a negativity (N2) at occipital electrodes and a positivity (P2) at the vertex. The degree of true motion processing reflected by N2 and P2 was estimated from the direction specificity of motion adaptation. Adapting stimuli moved to the right and test stimuli (random dot patterns of 26 degrees diameter; 10% contrast; 10.5 degrees /s velocity) moved in one of eight directions, which differed by 45 degrees. VEPs were recorded from occipito/temporal and central sites in eight subjects. Two adaptation effects were observed for N2 (P<0.01): a global amplitude reduction by 47% and a direction-specific reduction by a further 28%. For P2, only the global effect (54%; P<0.01) was observed. The global adaptation effect could also be induced by pattern reversal and pattern-onset adaptation, i.e. stimuli containing ambiguous or very little motion energy, respectively. We conclude that at least 28% of the N2 amplitude reflects the activity of direction-specific elements, whereas P2 does not at all.

Adaptation, Physiological↗
PubMed2004

Unconscious orientation processing.

Recent findings have shown that certain attributes of visual stimuli, like orientation, are registered in cortical areas when the stimulus is unresolvable or perceptually invisible; however, there is no evidence to show that complex forms of orientation processing (e.g., modulatory effects of orientation on the processing of other features) could occur in the absence of awareness. To address these questions, different psychophysical paradigms were designed in six experiments to probe unconscious orientation processing. First we demonstrated orientation-selective adaptation and color-contingent orientation adaptation for peripheral unresolvable Gabor patches. The next experiments showed the modulatory effects of perceptually indiscriminable orientations on apparent motion processing and attentional mechanisms. Finally we investigated disappearance patterns of unresolvable Gabor stimuli during motion-induced blindness (MIB). Abrupt changes in local unresolvable orientations truncated MIB; however, orientation-based grouping failed to affect the MIB pattern when the orientations were unresolvable. Overall results revealed that unresolvable orientations substantially influence perception at multiple levels.

Adaptation, Physiological↗
PubMed2004

Experience can change the 'light-from-above' prior.

To interpret complex and ambiguous input, the human visual system uses prior knowledge or assumptions about the world. We show that the 'light-from-above' prior, used to extract information about shape from shading is modified in response to active experience with the scene. The resultant adaptation is not specific to the learned scene but generalizes to a different task, demonstrating that priors are constantly adapted by interactive experience with the environment.

Adaptation, Physiological↗
PubMed2003

Selective induction of matrix metalloproteinases by Borrelia burgdorferi via toll-like receptor 2 in monocytes.

Regulation of secretion of matrix metalloproteinase (MMP) underlies the basis of numerous physiological and pathological processes in multicellular organisms. The Toll receptor family, which is conserved from Drosophila species to humans, mediates pattern recognition of a diversity of ligands involved in morphogenesis and innate immunity. Here, we show that secretion of MMP-9 is selectively induced through Toll-like receptor (TLR) 2 in human and murine monocytic cells stimulated with Borrelia burgdorferi. Secretion of MMP-1 was shown to be stimulated through a pathway other than TLR2, under identical conditions. Analysis of nuclear extracts indicated that activator protein (AP)-1 was reduced in TLR2-neutralized monocytic cells, suggesting that AP-1 plays a role in the transcriptional activation of MMP-9 through TLR2. The specific induction of MMP-9 through TLR2 provides direct evidence of a new role for this ancient receptor family in regulating secretion of MMPs and demonstrates evolutionary convergence between invertebrate morphogenesis and the vertebrate innate immune system.

Animals↗
PubMed1984

Generation of biological pattern and form.

We propose two models for pattern formation in early embryogenesis. The first deals with patterns in motile mesenchymal cells; the second treats patterns in epithelial sheets. In the mesenchymal model, cells exert tractions which deform the extracellular matrix within which they move. This in turn affects their motion. The model field equations are formulated and analysed, and applied to two widely studied phenomena: skin-organ primordia for feather and scale patterns, and the development of cartilage patterns in limb bone formation. The model for epithelial pattern formation consists of viscoelastic field equations with a calcium-controlled contraction trigger. Preliminary analysis is presented which demonstrates the existence of travelling wave solutions.

Animals↗
PubMed2005

Influence of the vagus nerve on respiratory patterns during early maturation.

Nonlinear dynamical analysis was performed on the phrenic neurogram before and after vagotomy in order to study the influence of the vagus nerve on the complexity of the phrenic neurogram in piglets in three age groups: 3-7 days (n = 7); 11-19 days (n = 6); and 29-34 days (n = 8). The phrenic neurogram, generated by the respiratory neural networks in the medulla, projects on the diaphragm muscles and initiate the respiratory movement. On the other hand, the vagus nerves carry the information from mechanoreceptors, located at the lower airway and lungs, to the medulla. The data was recorded during normal breathing (eupnea) before and after vagotomy while piglets were ventilated with 40% O2 in N2 and analyzed using the approximate entropy (ApEn) method. The mean values of the approximate entropy before and after vagotomy during the first 7 days of the postnatal age were 1.32 +/- 0.1 (standard deviation) and 1.34 +/- 0.07, respectively. These values before and after vagotomy during the 11-19 days age group were 1.15 +/- 0.09 and 1.12 +/- 0.05, respectively. For the 29-34 days age group, they were 1.14 +/- 0.05 before vagotomy and 1.19 +/- 0.08 after vagotomy. These differences in the ApEn (complexity) values of the phrenic neurogram before and after vagotomy are not statistically different at each age group. However, the mean mean approximate entropy (complexity) values between the 3-7 days age group and the other two groups were significantly different both before and after vagotomy (p < 0.05) using an analysis off variance test. These results suggest that the vagus nerve may not be mature during early maturation in piglets.

Action Potentials↗
PubMed2005

Automatic measurement of dermal thickness from B-scan ultrasound images using active contours.

BACKGROUND/PURPOSE: Measurement of dermal thickness is useful in the evaluation of dermo-cosmetics for assessing not only morphological changes but also mechanical properties of this layer. Our aim was first to standardise the manual dermal thickness measurement procedure on B-scan ultrasound images, then to develop an automatic operator independent method to detect the boundaries of the dermis. MATERIAL AND METHODS: The Dermcup 20 MHz B-scan ultrasound system was used. The method used for detecting the boundaries was adapted from active contour algorithms. The innovative aspect of the method consists in an automatic initialization of the first step of the algorithm. To validate the method, we correlated measurements obtained by the manual and automatic approaches from a set of images from different anatomical sites. RESULTS AND CONCLUSION: The results showed for the two measurement methods, 72% of the images were perfectly correlated. The remaining images required manual initialization of the boundaries by a non-expert operator before the active contour process could be used. Subsequent to this semi-automatic procedure, the correlation was very high.

Algorithms↗
PubMed1999

Rapid adaptation in visual cortex to the structure of images.

Complex cells in striate cortex of macaque showed a rapid pattern-specific adaptation. Adaptation made cells more sensitive to orientation change near the adapting orientation. It reduced correlations among the responses of populations of cells, thereby increasing the information transmitted by each action potential. These changes were brought about by brief exposures to stationary patterns, on the time scale of a single fixation. Thus, if successive fixations expose neurons' receptive fields to images with similar but not identical structure, adaptation will remove correlations and improve discriminability.

Action Potentials↗
PubMed1994

Human luminance pattern-vision mechanisms: masking experiments require a new model.

A widely used model of simultaneous luminance pattern masking is based on mechanisms that sum inputs linearly and produce a response that is an S-shaped function of that sum. This model makes two predictions about masking: (1) Changing the masker spatial waveform will shift the threshold-versus-masker contrast function horizontally by a multiplicative constant. (2) Adding a second fixed-contrast masker will shift this function horizontally by an additive constant. Experimental tests do not support these predictions. The results can be explained by a new model that incorporates broadband divisive inhibition, consistent with physiology.

Contrast Sensitivity↗
PubMed1988

Anatomy and physiology of visual evoked potentials and electroretinograms.

ERGs are electrical potentials originating in the retina and recorded directly from the corneal surface of the eyes. Flash ERGs are elicited by high intensity flashes either on scotopic or photopic conditions. The origin of the A and B waves of ERG are a combination of photoreceptor potentials, K+ mediated current flow and DC potentials within Müller cells, whereas the C waves are altered K+ fluxes induced by light in the pigment epithelia. Oscillatory potentials are probably related to feedback circuits of the inner layer of the retina. Electroretinograms evoked by pattern are mostly originated in ganglion cells. The use of various visual stimuli allow the selective activation of different retinal structures. Flashes selectively activate retina luminance and color detectors, whereas small pattern stimuli preferentially activate contrast and edge detectors. Visual evoked potentials recorded from the scalp probably originate from multiple cortical visual areas. P-100 response of the visual evoked potential to pattern stimulation is a cortically originated wave either produced exclusively by area 17 or 18 or by a multiplicity of cortical neuronal pools. Visual evoked potentials have important application for the diagnosis of optic nerve disease, assessment in conjunction with pattern ERG of the prognosis of recovery of visual function, and the evaluation of visual physiology and physiopathology.

Animals↗
PubMed1986

Medial hyperplasia obliterans of the intramural coronary arterial vessels.

Primitive structural changes of the tunica media of the intramural coronary small arterial branches have been observed in 52 per cent of 208 unexpected sudden coronary death cases and in 78 per cent of 97 normal subjects dying by accident. These changes consisted in hyperplasia and hypertrophy of the smooth muscle cells with longitudinal and oblique bundle formation, dramatic thickening of the media and fibrous replacement with lumen reduction. No aneurysms, inflammatory reaction or abnormal depositions have been observed. This process, defined as "Medial hyperplasia obliterans", showed a preferential location in the anterior papillary muscles, columnae carneae, superior interventricular septum. When present the number of "hyperplastic" vessels ranged from one to a maximum of forty-four per section. No relation was found with acute or chronic myocardial damage, heart weight, sex and age and sudden death. From the present data these medial structural changes and their aging appear to be a physiological response of the arterial wall to functional factors linked with the regional myocardial contraction. The correct recognition of this overlooked pattern seems important to avoid pathogenic misinterpretations and erroneous diagnosis of small vessel disease in case of endomyocardial biopsy.

Coronary Vessels↗
PubMed1997

Self-organising discovery, recognition and prediction of haemodynamic patterns in the intensive care unit.

To care properly for critically ill patients in the intensive care unit (ICU), clinicians must be aware of haemodynamic patterns. In a typical ICU, a variety of physiological measurements are made continuously and intermittently in an attempt to provide clinicians with the most accurate and precise data needed for recognising such patterns. However, the data are disjointed, yielding little information beyond that provided by instantaneous high/low limit checking. Although instantaneous limit checking is useful for determining immediate dangers, it does not provide much information about temporal patterns. As a result, the clinician is left to sift manually through an excess of data in the interest of generating information. In the study, an arrangement of self-organising artificial neural networks is used to automate the discovery, recognition and prediction of haemodynamic patterns in real time. It is shown that the network is capable of recognising the same haemodynamic patterns recognised by an expert system, DYNASCENE, without being explicitly programmed to do so. Consequently, the system is also capable of discovering new haemodynamic patterns. Results from real clinical data are presented.

Critical Care↗
PubMed1993

Pattern recognition in the neocognitron is improved by neuronal adaptation.

We demonstrate that equipping the neurons of Fukushima's neocognitron with the phenomenon that a neuron decreases its activity when repeatedly stimulated (adaptation) markedly improves the pattern discriminatory power of the network. By means of adaptation, circuits for extracting discriminating features develop preferentially. In the original neocognitron, in contrast, features shared by different patterns are preferentially learned, as connections required for extracting them are more frequently reinforced.

Adaptation, Physiological↗
PubMed2000

Steps in the formation of neurites and synapses studied in cultured leech neurons.

Leech neurons in culture have provided novel insights into the steps in the formation of neurite outgrowth patterns, target recognition and synapse formation. Identified adult neurons from the central nervous system of the leech can be removed individually and plated in culture under well-controlled conditions, where they retain their characteristic physiological properties, grow neurites and form specific chemical or electrical synapses. Different identified neurons develop distinctive outgrowth patterns that depend on their identities and on the molecular composition of the substrate. On native substrates, the patterns displayed by these neurons reproduce characteristics from the adult or the developing neurons. In addition, the substrate may induce selective directed growth between pairs of neurons that normally make contact in the ganglion. Upon contact, pairs of cultured leech neurons form chemical or electrical synapses, or both types depending on the neuronal identities. Anterograde and retrograde signals during membrane contact and synapse formation modify the distribution of synaptic terminals, calcium currents, and responses to 5-hydroxytryptamine.

Animals↗
PubMed2004

A novel role for an insect apolipoprotein (apolipophorin III) in beta-1,3-glucan pattern recognition and cellular encapsulation reactions.

Lipoproteins and molecules for pattern recognition are centrally important in the innate immune response of both vertebrates and invertebrates. Mammalian apolipoproteins such as apolipoprotein E (apoE) are involved in LPS detoxification, phagocytosis, and possibly pattern recognition. The multifunctional insect protein, apolipophorin III (apoLp-III), is homologous to apoE. In this study we describe novel roles for apoLp-III in pattern recognition and multicellular encapsulation reactions in the innate immune response, which may be of direct relevance to mammalian systems. It is known that apoLp-III stimulates antimicrobial peptide production in insect blood, enhances phagocytosis by insect blood cells (hemocytes), and binds and detoxifies LPS and lipoteichoic acid. In the present study we show that apoLp-III from the greater wax moth, Galleria mellonella, also binds to fungal conidia and beta-1,3-glucan and therefore may act as a pattern recognition molecule for multiple microbial and parasitic invaders. This protein also stimulates increases in cellular encapsulation of nonself particles by the blood cells and exerts shorter term, time-dependent, modulatory effects on cell attachment and spreading. All these responses are dose dependent, occur within physiological levels, and, with the notable exception of beta-glucan binding, are only observed with the lipid-associated form of apoLp-III. Preliminary studies also established a beneficial role for apoLp-III in the in vivo response to an entomopathogenic fungus. These data suggest a wide range of immune functions for a multiple specificity pattern recognition molecule and may provide a useful model for identifying further potential roles for homologous proteins in mammalian immunology, particularly in terms of fungal infections, pneumoconiosis, and granulomatous reactions.

Amino Acid Sequence↗
PubMed1980

N1-P2 correlates of reaction time at the single-trial level.

Using a template-matching pattern recognition technique evaluated in an earlier paper, the amplitude and latency of the N1-P2 wave of the vertex visual evoked potential was established on each trial of a reaction time task. This single-trial physiological information correlated meaningfully with trial-by-trial changes in performance, providing further indication of the validity and practicability of a single-trial approach to the analysis of human EP data.

Acoustic Stimulation↗
PubMed1975

Stimulus complexity, EEG abundance gradients, and detection efficiency in a visual recognition task.

Occipital EEG was monitored while subjects inspected 27 projected patterns. The number (N) and variety (V) of elements in the patterns were varied systematically. There were three levels of N (6, 12 or 24 elements) and three levels of V (circles, squares or hexagons occupying all, one half or one third of the element locations for all levels of N). Subjects were instructed that they would be required in a post-test to recognize the patterns, among patterns which had not appeared; they were also informed that the patterns had been constructed according to a set of simple rules, but the nature of these rules was not made fully explicit. The EEG was quantified by means of low-frequency analysis, yielding measures of abundance (theta, alpha and beta) and mean dominant frequency. For the recognition task, nine stimulus items were embedded among 45 items. Recognition efficiency was measured by means of the signal detection theory discrimination index (d'). The results were as follows: (i) Both N and V were inversely related to alpha abundance (P less than 0-01); (ii) the strongest relationship between stimulus parameters and the EEG held for N and EEG beta activity (13-5-19-5 Hz;P less than 0-001), where again the EEG and N were inversely related; (iii) there was a significant (P less than 0-05) direct relationship between N and theta activity; (iv) contrary to prediction, mean dominant alpha frequency decreased as N increased; (v) d' correlated significantly with a number of effects for N, i.e. subjects who exhibited greatest EEG discriminability of items during exposure of the patterns, subsequently obtained the higher detection scores in the recognition task. The work described therefore demonstrates that only only do stimulus parameters have systematic effects upon brain activity as measured by the EEG, but that such effects have functional value and reflect aspects of efficiency. The results are fully compatible with arousal theory constructs relating physiological reactivity and performance.

Adolescent↗