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J Holsheimer

Publications and source records attributed to J Holsheimer.

47 records · Page 3Linked to original sources
PubMed1987

Electrical conductivity of the hippocampal CA1 layers and application to current-source-density analysis.

The microstructure of the layers in the hippocampal CA1 area suggests that differences may exist between the electrical conductivities of these layers. In order to quantify these differences a sinusoidal current was applied to hippocampal slices in a bathing medium and potential differences were measured between pairs of neighbouring electrodes from an array. The maximum relative conductivity (100%) was found in the middle part of str. radiatum, with a gradual decrease towards the fissure (84%). There was also a gradual decrease towards the alveus (70%), but in str. pyramidale the relative conductivity was only 42%. No differences were observed between the laminar conductivities of normal hippocampal slices and slices generating spontaneous interictal bursts. These results were used to carry out a one-dimensional CSD analysis of field potentials evoked by Schaffer collateral stimulation. Despite the differences in conductivity, the homogeneous and the inhomogeneous CSD approximations did not lead to differences in the spatial distribution of sources and sinks and only gave some differences in the current density, especially at the pyramidal layer and its close environment.

Animals↗
PubMed1984

A simple method for the construction of electrode arrays.

A simple method is described for the construction of electrode arrays consisting of insulated metal wires (33 microns diameter) spaced at small, equal distances (0.1 mm). No specialized instrumentation and techniques are needed, as only simple mechanical tools are sufficient. The electrode arrays are used for field potential recording from in vitro brain slice preparations.

Animals↗
PubMed1983

Theta rhythm related hippocampal cell discharges in the urethane anaesthetized rat: evidence for a predominant entorhinal input.

Unit spike activity and slow wave field potentials were recorded in the CA1 pyramidal layer and the dentate granular layer of the dorsal hippocampus of urethane anaesthetized rats during theta rhythm. 70% of the units in the pyramidal layer and all units in the granular layer, having a discharge pattern related to theta rhythm, had their mean moment of discharge in the positive phase of the theta wave recorded in the pyramidal layer. Combined with the results of a modelling study (Holsheimer et al. 1982) it appears that in rat under urethane the theta modulated input to the CA1 pyramidal cells and the dentate granular cells will be mediated predominantly by pathways which terminate distally at these cells: the perforant path.

Action Potentials↗
PubMed1982

The double dipole model of theta rhythm generation: simulation of laminar field potential profiles in dorsal hippocampus of the rat.

A set of compartmental models of CA1 pyramidal, granular and polymorph cells of the dorsal hippocampus have been used to simulate membrane potentials generated by synaptic activation at various levels along these cells. From the membrane potential distributions the field potentials in dorsal CA1 and the dorsal blade of the dentate area have been simulated using a model based on volume conduction theory. Field potential profiles similar to laminar profiles, found experimentally in the dorsal hippocampus during theta rhythm, could only be simulated by assuming (almost) simultaneous synaptic excitation of the 3 cell types at given sites. The results lead to 2 alternative models for the simultaneous excitation of CA1 pyramidal cells and dentate granular cells during theta rhythm. Other electrophysiological evidence favours the model in which the two neuronal populations are activated distally near the fissure.

Animals↗
PubMed1979

Dipole-like neuronal sources of theta rhythm in dorsal hippocampus, dentate gyrus and cingulate cortex of the urethane-anesthetized rat.

Spatial distribution of theta activity was investigated in the dorsal hippocampal formation and overlying neocortex of the urethane-anesthetized rat. Laminar phase profiles from semi-microelectrode penetartions showed approximately 180 degrees phase shifts combined with small amplitude values in stratum radiatum of CA1, instratum moleculare of the dentate gyrus and in layer V/VI of the cingulate cortex at theta peak frequency. Evidence has been presented that layers of neurons in CA1, in the dorsal granular layer and in the cingulate cortex are the sources of dipole-like theta field potentials. A strong linear relationship between the neuronal theta sources in hippocampal CA1, dentate area and cingulate cortex was found.

Animals↗
PubMed1978

[Influence of uncorrelated noise sources in parallel signal processing chains on the coherence function (author's transl)].

When linear relationships between bio-electrical signals have to be established, it is important to consider the possible influence of noise added to these signals during recording and processing. Using a model for the signal generation (Fig. 1A) and one for the signal processing (Fig. 1B), the influence of uncorrelated noise in parallel signal processing chains on the coherence function can be quantified (Fig. 2). This is illustrated by the results of electrophysiological experiments, in which field potentials have been recorded simultaneously by two electrodes in different parts of the rat brain.

Animals↗
PubMed1977

Volume conduction and EEG measurements within the brain: a quantitative approach to the influence of electrical spread on the linear relationship of activity measured at different locations.

When recording referentially brain field potentials with several electrodes at relatively small tip separations, a linear relationship between the simultaneously recorded signals may arise solely as a result of volume conduction (electrical spread). A method is described to quantify the linear relationship due to electrical spread in a situation with independent neuronal sources. In rat under urethane anaesthesia, records were made during theta activity in the hippocampus with two electrodes against a reference with electrode tip separations between 0--3 mm. Frequency analysis of EEG epochs and computation of coherence were carried out. As an estimate of linear relationship between the recorded signals due to electrical spread the mean value of coherence (cohm) of a frequency band outside the range containing most power of theta rhythm was calculated. The results show a fairly constant decay of cohm at increasing electrode separation, reaching a value of 0.1 at a distance varying between 0.8--1.4 mm. This means that neurones at a distance of 0.4--0.7 mm from a recording electrode make a contribution of -25 dB to a recorded signal of 0 dB. The results of a simple model of volume conduction producing linear relationship between two recorded signals are in good agreement with the experimental results. The influence of linear relationship of the activity of neurones on volume conduction properties and on coherence is discussed.

Animals↗