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Biomedical subjects

S Grossberg

Publications and source records attributed to S Grossberg.

At least 73 records · Page 4Linked to original sources
PubMed1993

Pulmonary changes induced by combined mouse beta-interferon (rMuIFN-beta) and irradiation in normal mice--toxic versus protective effects.

This study in normal mice was undertaken to investigate possible enhancement of pulmonary toxicity by interferon-beta (IFN-beta) combined with single doses of irradiation. A pharmacokinetic study preceded the toxicity study to determine the optimal route and timing of IFN administration. Graded single doses of radiation were combined with graded doses of IFN. Pulmonary toxicity was determined using endpoints of alveolar surfactant and procollagen in lung lavage fluid at 7 days, breathing frequency, lethality and histology. Increased lethality was seen when IFN was combined with irradiation at 12.5 Gy vs. irradiation alone. This occurred between 20 and 30 weeks post treatment with no increased breathing frequency or surfactant release, suggesting independent mechanisms of injury. Increased breathing frequency after 40 weeks, usually associated with fibrosis, was less pronounced for IFN treated vs. irradiation only controls. Ultrastructural studies at 72 weeks suggest reduced fibrosis in lungs of IFN treated vs. irradiation only controls. Supporting this was the finding that Procollagen III, a biosynthetic precursor of collagen, was increased in the lavage fluid at 7 days for all radiation doses but decreased with the addition of IFN at 12.5 and 15 Gy. Interferons can act either as sensitizers or radioprotectors, depending on the biological system and type of interferon. Our study suggests that while IFN-beta may increase the acute effects of radiation in the mouse lung, some protection from radiation-induced fibrosis, possibly related to alteration of immune mechanisms, may exist.

Animals↗
PubMed1993

Neural dynamics of motion perception: direction fields, apertures, and resonant grouping.

A neural network model of global motion segmentation by visual cortex is described. Called the motion boundary contour system (BCS), the model clarifies how ambiguous local movements on a complex moving shape are actively reorganized into a coherent global motion signal. Unlike many previous researchers, we analyze how a coherent motion signal is imparted to all regions of a moving figure, not only to regions at which unambiguous motion signals exist. The model hereby suggests a solution to the global aperture problem. The motion BCS describes how preprocessing of motion signals by a motion oriented contrast (MOC) filter is joined to long-range cooperative grouping mechanisms in a motion cooperative-competitive (MOCC) loop to control phenomena such as motion capture. The motion BCS is computed in parallel with the static BCS of Grossberg and Mingolla (1985a, 1985b, 1987). Homologous properties of the motion BCS and the static BCS, specialized to process motion directions and static orientations, respectively, support a unified explanation of many data about static form perception and motion form perception that have heretofore been unexplained or treated separately. Predictions about microscopic computational differences of the parallel cortical streams V1-->MT and V1-->V2-->MT are made--notably, the magnocellular thick stripe and parvocellular interstripe streams. It is shown how the motion BCS can compute motion directions that may be synthesized from multiple orientations with opposite directions of contrast. Interactions of model simple cells, complex cells, hyper-complex cells, and bipole cells are described, with special emphasis given to new functional roles in direction disambiguation for endstopping at multiple processing stages and to the dynamic interplay of spatially short-range and long-range interactions.

Animals↗
PubMed1992

A neural network model of adaptively timed reinforcement learning and hippocampal dynamics.

A neural model is described of how adaptively timed reinforcement learning occurs. The adaptive timing circuit is suggested to exist in the hippocampus, and to involve convergence of dentate granule cells on CA3 pyramidal cells, and N-methyl-D-aspartate (NMDA) receptors. This circuit forms part of a model neural system for the coordinated control of recognition learning, reinforcement learning, and motor learning, whose properties clarify how an animal can learn to acquire a delayed reward. Behavioral and neural data are summarized in support of each processing stage of the system. The relevant anatomical sites are in thalamus, neocortex, hippocampus, hypothalamus, amygdala and cerebellum. Cerebellar influences on motor learning are distinguished from hippocampal influences on adaptive timing of reinforcement learning. The model simulates how damage to the hippocampal formation disrupts adaptive timing, eliminates attentional blocking and causes symptoms of medial temporal amnesia. Properties of learned expectations, attentional focussing, memory search and orienting reactions to novel events are used to analyze the blocking and amnesia data. The model also suggests how normal acquisition of subcortical emotional conditioning can occur after cortical ablation, even though extinction of emotional conditioning is retarded by cortical ablation. The model simulates how increasing the duration of an unconditioned stimulus increases the amplitude of emotional conditioning, but does not change adaptive timing; and how an increase in the intensity of a conditioned stimulus 'speeds up the clock', but an increase in the intensity of an unconditioned stimulus does not. Computer simulations of the model fit parametric conditioning data, including a Weber law property and an inverted U property. Both primary and secondary adaptively timed conditionings are simulated, as are data concerning conditioning using multiple interstimulus intervals (ISIs), gradually or abruptly changing ISIs, partial reinforcement and multiple stimuli that lead to time-averaging of responses. Neurobiologically testable predictions are made to facilitate further tests of the model.

Animals↗
PubMed1992

Cortical dynamics of visual motion perception: short-range and long-range apparent motion.

This article describes further evidence for a new neural network theory of biological motion perception. The theory clarifies why parallel streams V1----V2, V1----MT, and V1----V2----MT exist for static form and motion form processing among the areas V1, V2, and MT of visual cortex. The theory suggests that the static form system (Static BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast and to direction-of-motion, whereas the motion form system (Motion BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast but sensitive to direction-of-motion. The theory is used to explain classical and recent data about short-range and long-range apparent motion percepts that have not yet been explained by alternative models. These data include beta motion, split motion, gamma motion and reverse-contrast gamma motion, delta motion, and visual inertia. Also included are the transition from group motion to element motion in response to a Ternus display as the interstimulus interval (ISI) decreases; group motion in response to a reverse-contrast Ternus display even at short ISIs; speed-up of motion velocity as interflash distance increases or flash duration decreases; dependence of the transition from element motion to group motion on stimulus duration and size, various classical dependencies between flash duration, spatial separation, ISI, and motion threshold known as Korte's laws; dependence of motion strength on stimulus orientation and spatial frequency; short-range and long-range form-color interactions; and binocular interactions of flashes to different eyes.

Attention↗
PubMed1991

Why do parallel cortical systems exist for the perception of static form and moving form?

This article analyzes computational properties that clarify why the parallel cortical systems V1----V2, V1----MT, and V1----V2----MT exist for the perceptual processing of static visual forms and moving visual forms. The article describes a symmetry principle, called FM symmetry, that is predicted to govern the development of these parallel cortical systems by computing all possible ways of symmetrically gating sustained cells with transient cells and organizing these sustained-transient cells into opponent pairs of on-cells and off-cells whose output signals are insensitive to direction of contrast. This symmetric organization explains how the static form system (static BCS) generates emergent boundary segmentations whose outputs are insensitive to direction of contrast and insensitive to direction of motion, whereas the motion form system (motion BCS) generates emergent boundary segmentations whose outputs are insensitive to direction of contrast but sensitive to direction of motion. FM symmetry clarifies why the geometries of static and motion form perception differ--for example, why the opposite orientation of vertical is horizontal (90 degrees), but the opposite direction of up is down (180 degrees). Opposite orientations and directions are embedded in gated dipole opponent processes that are capable of antagonistic rebound. Negative afterimages, such as the MacKay and waterfall illusions, are hereby explained as are aftereffects of long-range apparent motion. These antagonistic rebounds help to control a dynamic balance between complementary perceptual states of resonance and reset. Resonance cooperatively links features into emergent boundary segmentations via positive feedback in a CC loop, and reset terminates a resonance when the image changes, thereby preventing massive smearing of percepts. These complementary preattentive states of resonance and reset are related to analogous states that govern attentive feature integration, learning, and memory search in adaptive resonance theory. The mechanism used in the V1----MT system to generate a wave of apparent motion between discrete flashes may also be used in other cortical systems to generate spatial shifts of attention. The theory suggests how the V1----V2----MT cortical stream helps to compute moving form in depth and how long-range apparent motion of illusory contours occurs. These results collectively argue against vision theories that espouse independent processing modules. Instead, specialized subsystems interact to overcome computational uncertainties and complementary deficiencies, to cooperatively bind features into context-sensitive resonances, and to realize symmetry principles that are predicted to govern the development of the visual cortex.

Attention↗
PubMed1990

Biological and clinical effects of the combination of beta- and gamma-interferons administered as a 5-day continuous infusion.

A phase I trial involving continuous infusion of both beta- and gamma-interferon (IFN-beta and IFN-gamma) was conducted in 20 patients in order to determine whether combinations of high doses of IFN-beta and IFN-gamma were tolerable when administered under conditions which mimic conditions of in vitro antiproliferative studies. Patients received a 5-day continuous infusion of IFN-beta/IFN-gamma, followed by a 9-day rest period. Two cycles were administered. Doses of IFN-beta/IFN-gamma were escalated between 4 dose levels, with 5 patients per dose level. Dose-dependent side effects, consisting primarily of constitutional symptoms typical of those experienced with IFN, were observed. The maximally tolerated dose of continuous IFN-beta/IFN-gamma infusion was 3 x 10(6) units of IFN-beta and 200 micrograms of IFN-gamma. Dose-limiting side effects consisted of severe headache, fatigue, fever, and hepatic toxicity. No clinical responses were observed. Serum IFN was measurable only at the highest 3 dose levels. Only 5 patients (4 at the highest dose level) had total serum levels which exceeded 50 laboratory units/ml (55, 63, 800, 800, and 550 laboratory units/ml, respectively). In order to confirm the biological effectiveness of this schedule, we measured IFN-inducible proteins prior to therapy, 24 h after the initiation of the infusion, and at the completion of the 5-day infusion. 2'-5'-Oligoadenylate synthetase, serum beta 2-microglobulin, neopterin, and p78 levels all increased significantly, and serum tryptophan decreased significantly within 24 h after the initiation of treatment (P less than 0.0001). A dose-response effect was observed for serum beta 2-microglobulin, neopterin, and p78 (P less than 0.02). We retrospectively compared the results of this trial with those of another IFN-beta/IFN-gamma trial in which IFN-beta and IFN-gamma were administered by i.v. bolus. Within the limitations of a retrospective comparison, continuous infusion was less well tolerated than our previous schedule of bolus administration 3 times/week. However, the continuous infusion schedule appeared to be more effective in enhancing 2'-5'-oligoadenylate synthetase levels in mononuclear cells. We conclude that tolerable doses of IFN-beta and IFN-gamma do not result in serum IFN levels which produce significant synergistic antiproliferative responses in vitro. This study and other findings suggest that, unless higher doses can be achieved, combinations of IFN-beta and IFN-gamma are unlikely to have significant therapeutic activity.

2',5'-Oligoadenylate Synthetase↗
PubMed1989

A neural network architecture for preattentive vision.

Recent results towards development of a neural network architecture for general-purpose preattentive vision are summarized. The architecture contains two parallel subsystems, the boundary contour system (BCS) and the feature contour system (FCS), which interact together to generate a representation of form-and-color-and-depth. Emergent boundary segmentation within the BCS and featural filling-in within the FCS are herein emphasized within a monocular setting. Applications to the analysis of boundaries, textures, and smooth surfaces are described, as is a model for invariant brightness perception under variable illumination conditions. The theory shows how suitably defined parallel and hierarchical interactions overcome computational uncertainties that necessarily exist at early processing stages. Some of the psychophysical and neurophysiological data supporting the theory's predictions are mentioned.

Artificial Intelligence↗
PubMed1988

Lack of interferon production by dipyridamole.

Dipyridamole, previously reported to be an interferon (IFN) inducer in mice, was evaluated in 43 normal volunteers or cancer patients. At doses ranging from 150 mg orally to 887 mg intravenously, no serum antiviral activity suggesting IFN induction was observed.

Dipyridamole↗
PubMed1986

Neural dynamics of speech and language coding: developmental programs, perceptual grouping, and competition for short-term memory.

A computational theory of how an observer parses a speech stream into context-sensitive language representations is described. It is shown how temporal lists of events can be chunked into unitized representations, how perceptual groupings of past item sublists can be reorganized due to information carried by newly occurring items, and how item information and temporal order information are bound together into context-sensitive codes. These language units are emergent properties due to intercellular interactions among large numbers of nerve cells. The controlling neural networks can arise through simple rules of neuronal development: random growth of connections along spatial gradients, activity-dependent self-similar cell growth, and competition for conserved synaptic sites. Within these networks, a spatial frequency analysis of temporally evolving activity patterns leads to competitive masking of inappropriate list encodings in short term memory. The neurons obey membrane equations undergoing shunting recurrent on-center off-surround interactions. Several design principles are embodied by the networks, such as the sequence masking principle, the long-term memory invariance principle, and the principle of self-similar growth.

Auditory Pathways↗
PubMed1985

A neural theory of circadian rhythms: split rhythms, after-effects and motivational interactions.

A neural theory of the circadian pacemaker within the hypothalamic suprachiasmatic nuclei (SCN) is used to explain parametric data about mammalian operant behavior. The intensity, duration, and patterning of ultradian activity-rest cycles and the duration of circadian periods due to parametric (LL) and nonparametric (LD) lighting regimes are simulated. Paradoxical data about split rhythms and after-effects are explained using homeostatic and nonhomeostatic neural mechanisms that modulate pacemaker activity. These modulatory mechanisms enable the pacemaker to adjust to pervasive changes in its lighting regime, as during the passage of seasons, and to ultradian changes in internal metabolic conditions. The model circadian mechanisms are homologous to mechanisms that model hypothalamically mediated appetitive behaviors, such as eating. The theory thus suggests that both circadian and appetitive hypothalamic circuits are constructed from similar neural components. Mechanisms of transmitter habituation, opponent feedback interactions between on-cells and off-cells, homeostatic negative feedback, and conditioning are used in both the circadian and the appetitive circuits. Output from the SCN circadian pacemaker is assumed to modulate the sensitivity of the appetitive circuits to external and internal signals by controlling their level of arousal. Both underarousal and overarousal can cause abnormal behavioral syndromes whose properties have been found in clinical data. A model pacemaker can also be realized as an intracellular system.

Animals↗