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H Pockberger

Publications and source records attributed to H Pockberger.

27 records · Page 2Linked to original sources
PubMed1983

[Mechanism of the generation of evoked potentials in the rabbit neocortex].

This paper describes the analyses of evoked potentials recorded in different neocortical areas (Area precentralis 1 and 2, occipitalis 1 and 2) and elicited by different stimulation techniques (antidromic stimulation of the pyramidal tract, electrical stimulation of thalamic nuclei, the optic nerve and finally random dot stimulation of the retina). Field potentials were recorded intracortically with a 16-fold electrode. The analyses of field potentials with the current-source-density method yielded an estimation of the current source and sink density distributions within the six neocortical layers. Hence spatio-temporal patterns of layer specific activation processes (sinks and sources) can be described for the various evoked potentials. The results can be summarized as follows: every evoked potential shows a spatio-temporal pattern of sources and sinks which is independent of the neocortical area and the mode of stimulation. However, the late components of the evoked potentials show great variations in their generation mechanisms, thus indicating regional differences in neocortical architectonics. These observations are discussed with regard to morphology, electrical activity and functional properties of the studied neocortical areas.

Animals↗
PubMed1982

The contribution of the cortical layers to the generation of the EEG: field potential and current source density analyses in the rabbit's visual cortex.

Intracortical spontaneous field potentials (EEG) were simultaneously recorded from the different layers of the rabbit's visual cortex using multielectrodes produced by thin-film technology. The signals were subjected to spectral analyses. Additionally, current source density analysis was applied to spontaneous delta waves. The results are based on 10 experiments. The spontaneous EEG of the rabbit's visual cortex consists mainly of slow delta waves. The spectral analytical studies of the delta band showed maximum power in layers I and II and in layers V and VI. Significant power minima were found in the middle layers IV and/or III. Essentially, the zones of power minima agree with the zones of minimum coherence and those zones where a phase reversal is observed. These properties of the intracortical spontaneous delta activity are best described as dipole-like. The spontaneous delta waves can be surface negative or surface positive; accordingly they show different source-sink distributions from which different generation mechanisms can be inferred. The possible mechanisms for the generation of these current source-sink distributions (dipoles) are discussed, taking into consideration the cortical anatomy. In many cases these discussions must be speculative because, for an unambiguous explanation of the observed phenomena, a much better knowledge of the cortical anatomy, the fibre connections with other cortical anatomy, the fibre connections with other cortical areas and with the deep cerebral structures is necessary.

Alpha Rhythm↗
PubMed1981

Current source density analysis: methods and application to simultaneously recorded field potentials of the rabbit's visual cortex.

This paper deals with the application of current source density (CSD) analysis to simultaneously recorded intracortical field potentials of the rabbit's visual cortex. Recordings were made with multielectrodes with either 8 contacts at distances of 300 microns, or 16 contacts at distances of 150 microns on one carrier needle. For synchronized activities, a spatial resolution of 150 microns turned out to be sufficient to record all depth-varying details of the field potentials; for seizure potentials even a spacing of 300 microns was adequate in most cases. For practical application, an appropriate spacing of the measuring points has to be chosen for a satisfactory estimation of the first and second derivatives of the field potentials. For this reason an interpolation procedure is applied to reduce the spacing from 300 microns or 150 microns electrode contact distances, respectively, and to obtain intermediate values at 75 microns distances. With this spacing satisfactory estimations of the second derivative are obtained. Theoretically, CSD analysis has to be made three-dimensionally, but under certain conditions which are discussed, a one-dimensional analysis can be applied. An unknown quantity is sigma z, the vertical conductivity. It turned out that average values obtained from different experiments are not representative and that the vertical conductivity has to be measured in every experiment. This is caused by the great individual differences of the cortices even if the same stereotactic coordinates are chosen. Therefore, in every experiment relative conductivity measurements are performed. The influence of different conductivity values within the various layers and the influence of a conductivity gradient is discussed and demonstrated by examples.

Animals↗
PubMed1981

[The effect of clonazepam on visual evoked potentials of the rabbit (author's transl)].

This paper deals with the action of Clonazepam on the cortical responses to visual stimuli in the rabbit. Epicortical as well as intracortical recordings from the different laminae were made by means of a multi-electrode made by thin film technology (13). Clonazepam was given intravenously in a dosis of 0.5 or 1.0 mg/kg body weight. The surface recordings showed that the visual evoked potentials (VEP) was, under the influence of the drug, altered only with respect to its secondary components. Those components which seem to originate within the zone of bilateral projection from both eyes are mostly influenced. The long lasting surface negative late component of the VEP was abolished by the action of the drug, and low-amplitude oscillations were seen instead. Within the different laminae of the visual cortex all components were altered in amplitude and latency. This phenomenon was most prominent within the zone of bilateral projection. Instead of two major negative components in the deep cortical layers, many positive and negative peaks were observed after the application of Clonazepam. This corresponds partly with the findings on the surface of the cortex. These results are discussed with respect to the manyfold mechanisms of action of Clonazepam.

Animals↗
PubMed1981

[Influence of clonazepam on interictal penicillin-spikes (author's transl)].

This paper deals with the action of Clonazepam on Penicillin induced interictal discharges. In 7 rabbits Penicillin was applied epicortically in a concentration of 25,000 or 50,000 I.U. The intracortical recordings were made with an 8 fold electrode, made by thin-film technology. Clonazepam (0.5 or 1.0 mg/kg) was given intravenously 30 to 45 min after the Penicillin application. Under Clonazepam the occurrence of double-und multiple interictal discharge is abolished. Single spikes become shorter and are significantly reduced in amplitude. Current Source-Density analysis showed that the configuration of sources and sinks is not altered under the action of this drug. However the spatio-temporal distribution is reduced drastically. If the shape of interictal spikes is compared by means of averaging technique before and after the application of Clonazepam, one observes a significant decrease in the standard deviation. These results indicate that excitatory processes are reduced by an enhancement of inhibitory phenomena within the cerebral cortex.

Animals↗
PubMed1976

[Intracortical electrogenesis: spontaneous activity, sleep and epileptic seizure (author's transl)].

Various electrical activities were recorded in rabbits from within the cortex by means of a multielectrode carrying, on a glass needle, 8 Ag-AgCl contacts (50X50 micronm) at 300 micronm distances. The records were stored on tape and analyzed (power spectrum, coherence and phase). Generally, the relatively uniform pattern of the cortical surface is paralleled by a spatio-temporally very complex intracortical activity. In all activities a zone of minimum activity ("zero zone") was found between roughly 500 and 800 micronm below surface. Beyond this zone, activities often appear like a mirrorimage of the surface activities although true phase-reversals never occur. In spontaneous activities this zone remains constant, during seizures it may shift and broaden. The maximum power is usually found below this zone. The transcortical power profile often changes during seizures. Tonic patterns, although fairly uniform in the ECoG from the surface of the cortex, turn out to be composed of several components when studied intracortically. The "generator zones" of the various intracortically identifiable graphoelements have various vertical position and extension. These findings demonstrate that a certain neuronal circuitry may be responsible for the shape of the potential recorded. This circuitry is far from rigid but may change in different stages of synchronization. For a better spatio-temporal resolution of intracortical activities, the interelectrode distance has still to be reduced.

Animals↗