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At least 955 records · Page 53Linked to original sources
PubMed1992

Ciliary beating in three dimensions: steps of a quantitative description.

We document a novel approach for quantitative assessment of ciliary activity, exemplified in rapid three-dimensional cyclic motion of the frontal cirri of Stylonychia. Cells held under voltage-clamp control are stimulated by step pulses to elicit reproducible hyperpolarization- or depolarization-induced ciliary motor responses. High-speed video recording at 200 fields per second is used for imaging ciliary organelles of the same cell in two perspectives: the axial view and, following cell rotation by 90 degrees, the lateral view. From video sequences of typically 1 s, the contours of the cirral images are determined and digitized. Computer programs are established to (1) reduce an observed image to a "ciliary axis", (2) sort series of axes by template to generate an averaged ciliary cycle in 2D-projection, and (3) to associate the generalized axial and lateral 2D-images for generation of a sequence of three-dimensional images, which quantitatively represent the cycle in space and time. The method allows us to produce predetermined perspectives of images selected from the ciliary cycle, and to generate stereo views for graphical representation of ciliary motion. The approach includes a potential for extraction of the complete microtubular sliding program of a cilium under reproducible electric stimulation of the ciliary membrane.

Animals↗
PubMed1991

Speech recognition by an artificial neural network using findings on the afferent auditory system.

An artificial neural network which uses anatomical and physiological findings on the afferent pathway from the ear to the cortex is presented and the roles of the constituent functions in recognition of continuous speech are examined. The network deals with successive spectra of speech sounds by a cascade of several neural layers: lateral excitation layer (LEL), lateral inhibition layer (LIL), and a pile of feature detection layers (FDL's). These layers are shown to be effective for recognizing spoken words. Namely, first, LEL reduces the distortion of sound spectrum caused by the pitch of speech sounds. Next, LIL emphasizes the major energy peaks of sound spectrum, the formants. Last, FDL's detect syllables and words in successive formants, where two functions, time-delay and strong adaptation, play important roles: time-delay makes it possible to retain the pattern of formant changes for a period to detect spoken words successively; strong adaptation contributes to removing the time-warp of formant changes. Digital computer simulations show that the network detect isolated syllables, isolated words, and connected words in continuous speech, while reproducing the fundamental responses found in the auditory system such as ON, OFF, ON-OFF, and SUSTAINED patterns.

Acoustic Stimulation↗
PubMed1975

Optokinetic nystagmus during selective retinal stimulation.

Nystagmic eye movements in response to selective optokinetic stimulation of different parts of the retina were studied in normal human subjects by two methods: 1. a digital computer controlled by the eye movement signal was used to generate an optokinetic display which stimulated only the peripheral retina, simulating a central scotoma, and 2. a single dot of 0.6 degrees in diameter was used as the stimulus during maintained forward gaze. The results show that stimulation of the central or peripheral retina alone can produce optokinetic nystagmus in man, and that essentially the same type of nystagmus is produced in both cases. The slow phase velocity of nystagmus evoked from the peripheral retina falls off rapidly with distance from the fovea but can be facilitated by attention. Results are compared with other findings and a possible explanation is offered for the observed variation in slow phase speed which occurs during constant velocity optokinetic stimulation.

Adolescent↗
PubMed1981

Dynamic mode LSF measurements for the scintillation camera.

A method is presented to improve the measurements of line spread function (LSF) of gamma cameras that makes use of a digital computer and a moving line source of radioactivity. Data acquisition is done in the dynamic mode with the computer, while the source moves across the collimator face. The resulting LSFs are defined with many curve points that enable very precise calculation of the corresponding modulation transfer function (MTF). The method is easily used in routine checking of gamma cameras. It makes possible a quick and precise determination of LSF for any point in the field of view of the detector.

Methods↗
PubMed1978

Dynamic radionuclide phlebography. A clinical study in patients after total hip replacement.

Dynamic radionuclide phlebography was performed in 50 consecutive patients after total hip replacement to evaluate the diagnostic value of the method compared to contrast phlebography. The investigation was limited to the diagnosis of iliofemoral thrombi. A special injection technique was developed and flow curves, mean transit time and distribution of flow were recorded with a scintillation camera interfaced to a digital computer. Three principally different types of flow curves were observed. Mean transit time was of value in differentiating particle flow in the superficial veins from passage through the deep veins. Out of 15 legs with thrombi in the iliofemoral region, the distribution of flow was significantly changed in 12. Deep vein thrombosis in the lower leg did not influence mean transit time or distribution of flow in the iliofemora region. Extensive collateral flow was rare. Ninety per cent of the thrombi were asymptomatic. The method compares favorably with the 125 I fibrinogen method and cuff impedance phlebography, in diagnosing iliofemoral thrombi after total hip replacement.

Hip Joint↗
PubMed1980

A mathematical model of canine granulocytopoiesis.

The granulocyte cell renewal system of the dog is represented by a mathematical model consisting of the following compartments: The pool of pluripotential stem cells, the committed stem cell pool, divided into a blood and a bone marrow compartment, the proliferation pool, the maturation pool, the reserve pool and the blood pool of functional granulocytes. This chain of compartments is described by a system of non-linear differential equations. Cell losses anyplace in the system provoke increased production in all pools containing cells capable to divide. A reduced number of granulocytes in the blood pool stimulates production of a "granulocyte releasing factor" which mobilizes a rising number of cells to transit from the marrow reserve into the blood pool. The model was simulated on a digital computer. It was found to be capable to reproduce the steady state conditions and it also fits the data of two distinct experimental perturbations of the system both equally well. These perturbations are a loss of proliferating cells as it occurs after the administration of cytostatic drugs and losses of functional cells as they are induced by leukapheresis experiments of differing leukapheresis rates.

Animals↗
PubMed1983

Four neural circuit models and their role in the organization of voluntary movement.

Four neural circuit models and their role in the organization of voluntary movement are presented here. These circuits collectively control a ballistic type biped voluntary movement. The structure of each circuit, and its function is discussed. Three of the circuits are central and contribute to the construction of two classes of inputs, analogous to the alpha signals and gamma signals in biological systems. The fourth circuit plays a role in stabilization of the movement, and in compensation for the receptors. Digital computer simulations are undertaken to demonstrate the construction of all the intermediate signals and the response of a two link biped to these efferent signals.

Animals↗
PubMed1980

A new hypothesis for synaptic modification: an interactive process between postsynaptic competition and presynaptic regulation.

Based on recent physiological observations, a new hypothesis for the algorithm for synaptic modification is proposed: an interactive process between postsynaptic competition and presynaptic regulation controls the synaptic modification, and both functions obey the same competitive rule. A fundamental algorithm for the competitive rule is proposed and analysed. The interactive process is deomposed into two procedures. The first one is a postsynaptic competition, in which all synapses making contact with the same postsynaptic cell compete for their terminal sites, and the postsynaptic cell makes demands for synaptic modification upon the presynaptic cells. The second one is a presynaptic regulation, in which the presynaptic cell regulates the postsynaptic demands and determines the net amount of the modification for each snyapse originating from it. The performance of the alforithm has been simulated on a digital computer. The initial structure of the simulated neural network consists of randomly-connected presynaptic and postsynaptic cells, with no other structures assumed. After repetitive presentations of a uniform stimulus, the basic configurations of neural connections (one-to-one, one-to-many, many-to-one and many-to-many connections) are organized in dependence on the parameters of the algorithm.

Axonal Transport↗
PubMed1978

An inference upon the neural network finding binocular correspondence.

Previously, the authors proposed a model of neural network extracting binocular parallax (Hirai and Fukushima, 1975). It is a multilayered network whose final layers consist of neural elements corresponding to "binocular depth neurons" found in monkey's visual cortex. The binocular depth neuron is selectively sensitive to a binocular stimulus with a specific amount of binocular parallax and does not respond to a monocular one. As described in the last chapter of the previous article (Hirai and Fukushima, 1975), when a binocular pair of input patterns consist of, for example, many vertical bars placed very closely to each other, the binocular depth neurons might respond not only to correct binocular pairs, but also to incorrect ones. Our present study is concentrated upon how the visual system finds correct binocular pairs or binocular correspondence. It is assumed that some neural network is cascaded after the binocular depth neurons and finds out correct binocular correspondence by eliminating the incorrect binocular pairs. In this article a model of such neural network is proposed. The performance of the model has been simulated on a digital computer. The results of the computer simulation show that this model finds binocular correspondence satisfactorily. It has been demonstrated by the computer simulation that this model also explains the mechanism of the hysteresis in the binocular depth perception reported by Fender and Julesz (1967).

Computers↗
PubMed1980

Neocognitron: a self organizing neural network model for a mechanism of pattern recognition unaffected by shift in position.

A neural network model for a mechanism of visual pattern recognition is proposed in this paper. The network is self-organized by "learning without a teacher", and acquires an ability to recognize stimulus patterns based on the geometrical similarity (Gestalt) of their shapes without affected by their positions. This network is given a nickname "neocognitron". After completion of self-organization, the network has a structure similar to the hierarchy model of the visual nervous system proposed by Hubel and Wiesel. The network consists of an input layer (photoreceptor array) followed by a cascade connection of a number of modular structures, each of which is composed of two layers of cells connected in a cascade. The first layer of each module consists of "S-cells", which show characteristics similar to simple cells or lower order hypercomplex cells, and the second layer consists of "C-cells" similar to complex cells or higher order hypercomplex cells. The afferent synapses to each S-cell have plasticity and are modifiable. The network has an ability of unsupervised learning: We do not need any "teacher" during the process of self-organization, and it is only needed to present a set of stimulus patterns repeatedly to the input layer of the network. The network has been simulated on a digital computer. After repetitive presentation of a set of stimulus patterns, each stimulus pattern has become to elicit an output only from one of the C-cells of the last layer, and conversely, this C-cell has become selectively responsive only to that stimulus pattern. That is, none of the C-cells of the last layer responds to more than one stimulus pattern. The response of the C-cells of the last layer is not affected by the pattern's position at all. Neither is it affected by a small change in shape nor in size of the stimulus pattern.

Cognition↗
PubMed1980

An algebraic model of an associative noise-like coding memory.

A mathematical model of an associative memory is presented, sharing with the optical holography memory systems the properties which establish an analogy with biological memory. This memory system--developed from Gabor's model of memory--is based on a noise-like coding of the information by which it realizes a distributed, damage-tolerant, "equipotential" storage through simultaneous state changes of discrete substratum elements. Each two associated items being stored are coded by each other by means of two noise-like patterns obtained from them through a randomizing preprocessing. The algebraic transformations operating the information storage and retrieval are matrix-vector products involving Toeplitz type matrices. Several noise-like coded memory traces are superimposed on a common substratum without crosstalk interference; moreover, extraneous noise added to these memory traces does not injure the stored information. The main performances shown by this memory model are: i) the selective, complete recovering of stored information from incomplete keys, both mixed with extraneous information and translated from the position learnt; ii) a dynamic recollection where the information just recovered acts as a new key for a sequential retrieval process; iii) context-dependent responses. The hypothesis that the information is stored in the nervous system through a noise-like coding is suggested. The model has been simulated on a digital computer using bidimensional images.

Computers↗
PubMed1983

A systems model for the pupil size effect. I. Transient data.

The human pupillary control system is a paradigm for linearized biological control systems. It also exhibits a series of interesting nonlinear behaviors, particularly asymmetry, "pupillary escape," and "pupillary capture." We present a nonlinear model in which a signal dependent upon pupil size is fed back internally to cause a change in system parameters related to gains and rates of light adaptation. The model was simulated on a digital computer, a variety of experimental data was well matched, and improvements over previous pupil models demonstrated. A candidate physiological mechanism for adaptive components of the model might have the form of an inverse "Henneman coded" neuronal pool.

Animals↗
PubMed1985

Systems model for pupil size effect. II. Feedback model.

The human pupillary control system has been the subject of interest to biologists and engineers as an example of a sensorimotor reflex which can be embedded in a control system paradigm. We present a nonlinear feedback model whose compact structure allows us to hypothesize possible physiological mechanisms which generate the proper behavior of the pupil system. The important pupil responses, including pupil size effect, asymmetry, and response the high-frequency stimuli, are defined. This model was simulated on a digital computer and comparisons to the paradigm experimental responses were performed, demonstrating a fit to each of the observed conditions. Improvements on previous models are discussed.

Feedback↗
PubMed1980

A template matching model for pattern recognition: self-organization of templates and template matching by a disinhibitory neural network.

A template matching model for pattern recognition is proposed. By following a previously-proposed algorithm for synpatic modification (Hirai, 1980), the template of a stimulus pattern is self-organized as a spatial distribution pattern of matured synapses on the cells receiving modifiable synapses. Template matching is perfomed by the disinhibitory neural network cascaded beyond the neural layer composed of the cells receiving the modifiable synapses. The performance of the model has been simulated on a digital computer. After repetitive presentations of a stimulus pattern, a cell receiving the modifiable synapses comes to have the template of that pattern. And the cell in the latter layer of the disinhibitory neural network that receives the disinhibitory input from that cell becomes selectively sensitive to that pattern. Learning patterns are not restricted by previously learned ones. They can be subset or superset patterns of the ones previously learned. If an unknown pattern is presented to the model, no cell beyond the disinhibitory neural network will respond. However, if previously learned patterns are embedded in that pattern, the cells which have the templates of those patterns respond and are assumed to transmit the information to higher center. The computer simulation also show that the model can organize a clean template under a noisy environment.

Animals↗
PubMed1988

A model for intersegmental coordination in the leech nerve cord.

The neuronal circuits that generate swimming movements in the leech were simulated by a chain of coupled harmonic oscillators. Our model incorporates a gradient of rostrocaudally decreasing cycle periods along the oscillator chain, a finite conduction delay for coupling signals, and multiple coupling channels connecting each pair of oscillators. The interactions mediated by these channels are characterized by sinusoidal phase response curves. Investigations of this model were carried out with the aid of a digital computer and the results of a variety of manipulations were compared with data from analogous physiological experiments. The simulations reproduced many aspects of intersegmental coordination in the leech, including the findings that: 1) phase lags between adjacent ganglia are larger near the caudal than the rostral end of the leech nerve cord; 2) intersegmental phase lags increase as the number of ganglia in nerve cord preparations is reduced; 3) severing one of the paired lateral connective nerves can reverse the phase lag across the lesion and 4) blocking synaptic transmission in midganglia of the ventral nerve cord reduces phase lags across the block.

Animals↗
PubMed1986

A neural network model for selective attention in visual pattern recognition.

A neural network model of the mechanism of selective attention in visual pattern recognition is proposed and simulated on a digital computer. When a complex figure consisting of two patterns or more is presented to the model, it is segmented into individual patterns, and each pattern is recognized separately. Even if one of the patterns to which the model is paying selective attention is affected by noise or defects, the model can recall the complete pattern from which the noise has been eliminated and the defects corrected. It is not necessary for perfect recall that the stimulus pattern should be identical in shape to the training pattern. Even though the pattern is distorted in shape or changed in size, it can be correctly recognized and the missing portions restored. The model consists of a hierarchical neural network which has efferent as well as afferent connections between cells. The afferent and the efferent signals interact with each other in the network: the efferent signals, that is, the signals for selective attention, have a facilitating effect on the afferent ones, and, at the same time, the afferent signals gate efferent signal flow. When some feature in the stimulus is not extracted in the afferent paths, the threshold for detection of that feature is automatically lowered by decreasing the efficiency of inhibition, and the model tries to extract even vague traces of the undetected feature.

Afferent Pathways↗
PubMed1980

Some methods and parameters of body sway quantification and their neurological applications.

Methods and parameters are described to quantify body sway as measured by a force-transducing platform. Analogue data representing the coordinates of the body's center of force (COF) are fed into a digital computer. Th following parameters are then calculated and tested for their diagnostic significance: sway path (SP), mean amplitude of sway (MA), mean sway frequency (MF), their lateral and sagittal components, and the quotients sagittal/lateral of these as well as the sway area (SA) circumscribed by the COF. Quotients of eyes open/eyes closed for all these parameters determine the visual stabilization of posture. Sway position and sway direction histograms allow for a more detailed analysis of MA and SP. Despite considerable inter- and intraindividual variance of these parameters (in 28 normals), some of them seem of clinical significance not only for documentation and follow-up studies but also for differential diagnosis. In patients with cerebellar lesions (n = 12), SP and MA were up to 10 times larger with a marked antero-posterior instability, MF being above normal. Patients with labyrinthine lesions (n = 10) showed significant instability only with eyes closed, MF being slightly below normal.

Cerebellar Ataxia↗
PubMed1984

Pharmacokinetics of mitomycin C in non-oat cell carcinoma of the lung.

The disposition kinetics of the cancer chemotherapeutic agent mitomycin C have been studied in six male patients receiving mitomycin C in combination with cisplatin and vinblastine for non-oat cell carcinoma of the lung. Following rapid IV administration of mitomycin C (10 mg/m2), serum concentration-time course data were biexponential, with biologic half-lives of 46.2 +/- 12.1 min (mean +/- SD). Pharmacokinetic analysis of data by the CSTRIP and NONLIN digital computer programs generated parameters which suggested extensive distribution (V area = 656.8 +/- 169.8 ml X kg-1, mean +/- SD) and, as reported for other alkylating agents, rapid elimination (total body clearance = 10.3 +/- 3.2 ml X kg-1 X min-1, mean +/- SD). Interpatient variations in pharmacokinetic parameters were relatively small, suggesting that close monitoring of mitomycin C therapy might be unnecessary in patients with normal renal and hepatic function.

Antibiotics, Antineoplastic↗