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Biomedical subjects

E Lábos

Publications and source records attributed to E Lábos.

At least 19 recordsLinked to original sources
PubMed1996

Long cycles and special categories of formal neuronal units and networks.

Composite categories of formal neurons or units (FN, FU) and their nets (FNN) are displayed. Long state cycles based on previously described methods in FNN-s are presented too. These results make easier any orientation among the immense number of possible cases of such nets. The taxonomical entities (classes, categories) give also cues for the synthesis of long and complicated cycles. The networks belong to the most complicated kind of net synthesis, thus realisations of other cases are expected to be easier. The observed wiring versus dynamics relationships give an insight into the real network control mechanisms and points to additional mechanisms for real nets. The work is a founded on previous results of the author.

Biological Clocks↗
PubMed1993

A unit paradox for artificial neuronal networks.

In formal or artificial neuronal networks (FNN; ANN) built of threshold logic gates, a unit step function is used. Recently the step function has been replaced by an S-shaped curve. This replacement is common and many studies are based on this substitution, often combined rarely not with some adaptive or learning procedure. However, the dynamical consequences e. g. in the time course of single unit discharges have not been sufficiently examined. The concepts of unit (neuron) and network in these models of engineering and neurobiology correspond to each other only partially: model units may behave similarly to real nets of real units. This is called here a unit paradox. Propositions are presented to eliminate this apparent contradiction. A further paradox is also mentioned (Section 3). It seems necessary to reconsider the relationship of the various trends of neural network theory.

Electroencephalography↗
PubMed1990

On the dynamics of triadic synaptic arrangements: computer experiments with formal neural nets of chaotic units.

Computer simulations were carried out in an attempt to understand the possible operating modes of synaptic triadic arrangements as described in the dorsal lateral geniculate nucleus of the monkey. Small networks of "chaotic" units (piecewise linear internal maps) were used to investigate their performance as ON-gates for the transmission of spikes. "Chaotic" units have advantages over "logic" units because the former are asynchronous, it is possible to simulate temporal summation, and also to adjust subthreshold time-constants. It was demonstrated that ensembles with single delay lines, representing "closely-packed" triads, were hardly capable of realizing reliable and efficient ON-gate operations. Networks with multiple delayed lines, patterned after triads "at a distance" coupled with "closely-packed" triads, were capable of secure ON-gate functions. Such gates were input dependent, becoming reliable only when high frequency bursts were used as the source of activity. Moreover, the ON-gate could be temporarily interrupted by square wave bursts applied to the inhibitory units, a situation resembling electron microscopic observations of interneuron to interneuron synapses in the LGNd.

Computer Simulation↗
PubMed1983

Entrainment of a bursting neuron--I. typical activity.

Highly regular RPA-1 oscillator neurons of the land snail Helix pomatia L. are tested for entrainment by rhythmical stimulation. Both with orthodromic and direct hyperpolarizing pulses the bursting activity could be entrained to frequencies higher or lower than, and equal to, the spontaneous one, in this order of difficulty. Depolarizing pulses give mainly entrainment to higher frequencies, but synchronization to frequencies lower than the spontaneous one was also demonstrable. Each of these different driving relations implies the consecutive stimuli to become locked to a peculiar range of phases and not to a single phase of resonance inside the cycle.

Animals↗
PubMed1983

Entrainment of a bursting neuron--II. Atypical cases.

Entrainment to external rhythms was analyzed in atypical RPA-1 neurons of Helix pomatia L. stimulated orthodromically. Neurons with long-lasting bursts were tested only with supraharmonic frequencies. All cycle-stimulus relations described for typical oscillators did occur, with particularities due to the frequency of stimulation and the strong fluctuations of cycle parameters. Activity in pairs or triplets was refractory to entrainment. Instead, rhythmical pulses may transform the bimodal activity into a monomodal one. Continuously active neurons and silent ones were also tested. Fragmentation into bursts and long-period bimodal activity could be evoked respectively, suggesting the presence of a latent bimodal pacemaker behind these activities.

Animals↗
PubMed1980

On the functional significance of axonal triads in medial cuneate nucleus.

Theoretical considerations are presented about the possible functional significance of special triadic synaptic arrangements in medial cuneate nucleus. Although they can not be regarded functionally equivalent to the dendritic triadic arrangements in the thalamic nuclei, the cuneate axonal triads are likely to participate not only in distance dependent stimulus discrimination, but also in movement perception.

Animals↗
PubMed1977

Theoretical considerations of local neuron circuits and their triadic synaptic arrangements (TSA) in subcortical sensory nuclei.

Certain sequential models of the so-called synaptic triadic arrangements (TSA) occurring in sensory nuclei are analyzed. The considerations are addressed mainly to the lateral geniculate body. The model is based on the assumption that the neurons establishing these triads consist of conditionally coupled decision-making subunits. It might be concluded that this and similar arrangements could play a role in the discrimination between stationary and moving retinal inputs and in the detection of temporal correlations in certain input channels.

Animals↗