Biomedical subjects

I Nelken

Publications and source records attributed to I Nelken.

22 records · Page 2Linked to original sources

PubMed1991

Neural interactions in the frontal cortex of a behaving monkey: signs of dependence on stimulus context and behavioral state.

In order to gain an understanding of the processes taking place within and between neuronal assemblies, we made simultaneous recordings of spike trains from groups of up to 11 neurons in the frontal cortex of a rhesus monkey, that was trained to perform a sensorimotor behavioral task. We report here on preliminary results from correlation analysis of these neuronal activities, with special emphasis on signs of behaviorally induced modifications of neural interaction, possibly due to rapid modulations of discharge synchronization among the neurons. Our findings suggest that different functional groups of neurons may co-exist within each small volume of cortex, and that neurons may be dynamically recruited into such a group to fulfil a specific function.

Animals↗

PubMed1990

A sensitive estimator for crosscorrelograms.

The best established method for finding interactions between extracellularly recorded neurons is the crosscorrelation technique. The method is simple and useful, but it has some drawbacks. One of them is its limited sensitivity to weak interactions, which are common in the mammalian cerebral cortex. In the present paper a new method for the estimation of interaction strength is presented. This method is based on the intensity representation of point processes, and provides an optimal estimator for the intensity of the postsynaptic spike train. The estimator is complicated to use, but it can be approximated by a simple estimator, similar to ordinary measures of synaptic efficacy like the area under the crosscorrelogram peak. Simulation results, showing the advantage of the new estimator over the commonly used efficacy estimators and some measure of its robustness to deviations from model assumptions, are presented. Finally, application of the estimator to the analysis of simultaneous recordings of physiological single units is demonstrated.

Animals↗

PubMed1988

Analysis of the activity of single neurons in stochastic settings.

This paper presents a new way of modeling the activity of single neurons in stochastic settings. It incorporates in a natural way many physiological mechanisms not usually found in stochastic models, such as spatial integration, non-linear membrane characteristics and non-linear interactions between excitation and inhibition. The model is based on the fact that most of the neuronal inputs have a finite lifetime. Thus, the stochastic input can be modeled as a simple finite markov chain, and the membrane potential becomes a function of the state of this chain. Firing occurs at states whose membrane potential is above threshold. The main mathematical results of the model are: (i) the input-output firing rate curve is convex at low firing rates and is saturated at high firing rates, and (ii) at low firing rates, firing usually occurs when there is synchronous convergence of many excitatory events.

Action Potentials↗

PubMedDate not supplied

The role of interstitial potassium in the generation of low-calcium hippocampal seizures.

The explosive nature of a focal cortical seizure suggests the operation of strong positive feedback in the neuronal network. It was previously proposed that in the hippocampus this may be provided by the regenerative accumulation of potassium in the interstitium. This hypothesis was severely criticized in the past. However, it gained new impetus with the recent discovery that focal seizures can arise in mammalian hippocampal slices perfused with low calcium solutions despite the block of chemical synaptic transmission. Here, we examine the relationship of interstitial potassium concentration to the electrogenesis of these low-calcium seizures. Both the experimental data and the behavior of a simplified mathematical model describing neuronal discharge in low calcium, support the contention that interstitial potassium accumulation may play an important role in the buildup of hippocampal seizures.

Animals↗