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R Elul

Publications and source records attributed to R Elul.

17 recordsLinked to original sources
PubMed1983

Artificial neural nets: dependence of the EEG amplitude's probability distribution on statistical parameters.

The statistical laws governing the output of a population of unitary generators are not explicit with regard to the effect of population size and properties of the individual generators on the summed activity. Experimental work was therefore undertaken with artificial nerve nets, the activity of which simulates with a high degree of realism individual nerve cells and the electroencephalogram. It was found that the summed activity is not affected by the statistical properties of single generators even in nets of only 200-1000 elements. On the other hand, the output of the net is highly sensitive to the level of connectivity between individual generators. When connectivity is low, the summed output is distributed in normal (Gaussian) fashion. The output of the net becomes less and less Gaussian with increase in coupling between the generators.

Animals↗
PubMed1982

Encoding of visual information: correlation of EEG response to intracellular response.

The intracellular average evoked response to full field flash in cat visual cortex was seen to have constant PSP correlates in every individual response, with a less constant relationship to spike activity. All components of the averaged evoked response in the gross EEG are explicable in the response of a single cell, including a component of latency 100 ms for which there is evidence of initiation at the apical dendrites. The data support the hypothesis that information about photostimulation is encoded at the level of the individual cell, with distortion resulting from extraneous "noise".

Animals↗
PubMed1976

The ionic basis of the membrane potential in a rat glial cell line.

Intracellular ionic concentrations, membrane potential and Na+ and K+ flux were measured in a clonal rat glial cell line, C6. Intracellular concentrations of C6 cells were: (mmole/liter cell water) K+ 145 +/- 4 S.D., Na+ 18 +/- 4 S.D., Cl- 14 +/- 1 S.D. Cells maintained a steady state level of K+ over the duration of the experiments. This was substantiated by the close agreement between absolute values for K+ influx and efflux measured with 42K. When cells were depleted of internal Na+, K+ influx was significantly reduced suggesting that a portion of inward K+ movement is linked to Na+ extrusion. Efflux of Na+, calculated from the half-time of exchange from cells preloaded with 22Na, was higher than passive Na+ influx determined by blocking Na+ extrusion with ouabain. Since cell Na+ concentration remained relatively constant, part of the Na+ efflux may be due to exchange diffusion. The average membrane potential of C6 cells uas -36 mV. The potential showed a 31 mV slope for a 10-fold change in external K+ so that it is determined predominantly by the ratio of external/internal K+. The potential however, consistent with the relatively large passive Na+ influx, was influenced by Na+. Replacing all but 20 mM external Na+ with choline hyperpolarized the membrane by 13 mV. The ratio of PNa/PK of 0.11 suggests that Na+ is outwardly transported to maintain the steady-state concentrations observed. Since these responses are similar to those in non-tumor glia, it suggests that the C6 cell line may provide a useful model for studying ionic regulation in glial cells.

Animals↗
PubMed1976

A linked active transport system for Na+ and K+ in a glial cell line.

Ouabain (5 X 10(-4) M) induced a 6-fold increase in intracellular Na+ and a 65% loss of cellular K+ in C6 glial cells which was accompanied by a 12 mV decrease in the resting membrane potential. Following ouabain washout intracellular ion concentrations and the membrane potential returned to control levels suggesting that C6 is capable of active Na+ transport which is linked to uptake of K+. A portion of K+ uptake under steady-state conditions is also active since K+ influx was reduced 32% by ouabain. Five mM cyanide significantly increased cell Na+ and significantly decreased cell K+ and the membrane potential. The similarity in the ratio of Na+ gained/K+ lost (ouabain 1.24, cyanide 1.41) suggests that the two agents inhibit the same ion transport system. Decreased temperature had the paradoxical effect of increasing intracellular K+ while significantly decreasing both membrane potential and K+ influx. Part of this effect may be due to the marked reduction in K+ efflux at low temperature. At 6 degrees C cell loss of K+ was much less than loss of K+ with ouabain at 37 degrees C. The observation of a linked Na+-K+ transport system in C6 cell confirms the hypothesis that coupled active Na+-K+ exchange occurs in glial cells and suggests that ionic transport may regulate certain aspects of glial metabolism.

Animals↗
PubMed1975

Non-Gaussian behavior of the EEG in Down's syndrome suggests decreased neuronal connections.

Computer analyses of the electroencephalograms of normal children, and children with Down's syndrome who were mentally retarded, revealed differences in the distribution of amplitude between the two groups. Normal children, in the early postnatal period, generate EEG's which have a non-Gaussian distribution of amplitude that becomes increasingly Gaussian before one year of age and remains so throughout subsequent development. Conversely, the EEG's of children with Down's syndrome exhibit highly non-Gaussian properties at all ages studied. The EEG's of two mentally retarded autistic children did not show this property, so it is not merely a concomitant of mental retardation. The first-order Gaussian distribution may reflect the degree of inteneuronal coupling; since an increased number of connections on any neuron implies decreased functional dependence of that neuron on any other particular single neuron, the present evidence, which indicates stronger interneuronal coupling in mongoloids, suggests that Down's syndrome may be associated with incomplete postnatal development of interconnections between cortical neurons.

Autistic Disorder↗
PubMed1974

Effect of structure on function in model nerve nets.

A theoretical analysis has been made on the effect of the pattern of interneuronal connectivity in model nerve nets on the activity of these nets. Two types of nets have been investigated: one in which the likelihood of a connection between a given neuron and any other element in the net is given by a Poisson probability distribution, and a second type in which the pattern of interconnection follows a Gaussian distribution. An analytical treatment is presented of the equations for noiseless nets in these two conditions. The principal result is that nets with Poisson connectivity law are activated by extraneous firing of a single neuron and continue in spontaneous activity indefinitely. On the other hand, similar nets in which the connections are, however, distributed according to a normal connectivity law, exhibit a definite threshold and produce spontaneous activity only subsequent to extraneous activation of a substantial fraction of the population. Moreover, spontaneous activity in Gaussian nets, but not in Poisson nets, becomes extinguished if the number of active neurons falls below the critical threshold. Some neuroanatomical implications are discussed which suggest that the pyramidal system of the cerebral cortex and other neuronal systems histologically characterized by large numbers of synapses per neuron may incorporate a Gaussian connectivity law, whereas a Poisson law may be characteristic of these cortical layers and nuclei primarily containing granule cells.

Electric Conductivity↗
PubMed1969

Gaussian behavior of the electroencephalogram: changes during performance of mental task.

The probability distribution of the amplitude of scalp electroencephalogram has been investigated in an adult subject in the idle state, and during performance of a mental arithmetic task. Based on a large sample, the electroencephalogram in this subject in the idle state follows a Gaussian (normal) probability function 66 percent of the time. During performance of the arithmetic task, the portion of Gaussian electroencephalogram decreases to 32 percent. The probability function characterizing gross electroencephalographic activity is determined by the degree of mutual interaction of individual cellular generators of wave activity in the tissue underneath the recording electrode. The data imply an increase in the cooperative activity of cortical neuronal elements during performance of a mental task.

Analog-Digital Conversion↗
PubMed1967

Fixed charge in the cell membrane.

1. Focal electric field was generated by passing a current of 5 x 10(-7) to 1 x 10(-5) A from a micropipette into the culture medium. Movement of cells at a distance of 5-50 mu from the electrode tip was observed. In case of cells embedded in the culture only local deformation of the membrane was observed.2. The cell species explored included neurones, glia, muscle fibres, connective cells, malignant cells and erythrocytes. All cells responded in a similar manner to the electric field, and the current required was in the same range.3. Cells were attracted to a positive micropipette and repelled from a negative one: the only exception was observed in certain malignant cells which moved in the opposite direction.4. Movement and membrane deformation could be obtained with electrodes filled with various concentrated and isotonic solutions. The composition of the culture medium also had no qualitative influence on these effects.5. Metabolic poisons or rupture of the cell membrane had no effect on the movement. Isolated membrane fragments showed movement similar to that of intact cells.6. The possibility of artifacts due to proximity of the focal electrode is considered. It is shown that electro-osmosis cannot account for the present observations. Some other artifacts are also excluded.7. It is proposed that the most satisfactory way to account for the present observations is by a membrane carrying negative fixed charge of the order of 2.5 x 10(3) e.s.u./cm(2). Some physiological consequences of presence of negative charge in the membrane are briefly discussed.

Animals↗