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C R Legéndy

Publications and source records attributed to C R Legéndy.

6 recordsLinked to original sources
PubMed1985

Bursts and recurrences of bursts in the spike trains of spontaneously active striate cortex neurons.

Simultaneous recordings were made from small collections (2-7) of spontaneously active single units in the striate cortex of unanesthetized cats, by means of chronically implanted electrodes. The recorded spike trains were computer scanned for bursts of spikes, and the bursts were catalogued and studied. The firing rates of the neurons ranged from 0.16 to 32 spikes/s; the mean was 8.9 spikes/s, the standard deviation 7.0 spikes/s. Bursts of spikes were assigned a quantitative measure, termed Poisson surprise (S), defined as the negative logarithm of their probability in a random (Poisson) spike train. Only bursts having S greater than 10, corresponding to an occurrence rate of about 0.01 bursts/1,000 spikes in a random spike train, were considered to be of interest. Bursts having S greater than 10 occurred at a rate of about 5-15 bursts/1,000 spikes, or about 1-5 bursts/min. The rate slightly increased with spike rate; averaging about 2 bursts/min for neurons having 3 spikes/s and about 4.5 bursts/min for neurons having 30 spikes/s. About 21% of the recorded units emitted significantly fewer bursts than the rest (below 1 burst/1,000 spikes). The percentage of these neurons was independent of spike rate. The spike rate during bursts was found to be about 3-6 times the average spike rate; about the same for longer as for shorter bursts. Bursts typically contained 10-50 spikes and lasted 0.5-2.0 s. When the number of spikes in the successively emitted bursts was listed, it was found that in some neurons these numbers were not distributed at random but were clustered around one or more preferred values. In this sense, bursts occasionally "recurred" a few times in a few minutes. The finding suggests that neurons are highly reliable. When bursts of two or more simultaneously recorded neurons were compared, the bursts often appeared to be temporally close, especially between pairs of neurons recorded by the same electrode; but bursts seldom started and ended simultaneously on two channels. Recurring bursts emitted by one neuron were occasionally accompanied by time-locked recurring bursts by other neurons.

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PubMed1984

A multiple floating microelectrode for chronic implantation and longterm single unit recording in the cat.

This paper describes a multiple electrode, suitable for chronic implantation and single unit recording in the superficial cerebral cortex of the cat. The electrodes are fine wires, 5-8 per implant, not kept together in a bundle; a segment of them floats freely in saline in a closed chamber over the place of penetration. The electrode tips are not sharpened electrolytically, but cut at a bevel during surgery. Longevity of the implants is improved by slowing down the occasional rapid head shaking characteristic of cats, which tends to tear out implanted electrodes, by means of a small weight attached by a bar to the head.

Animals↗
PubMed1978

Functional organization of the corticofugal system from visual cortex to lateral geniculate nucleus in the cat (with an appendix on geniculo-cortical mono-synaptic connections).

1. In the cat visual cortex (VC), electrophoretic glutamate application at a depth corresponding to layer VI may have excitatory or inhibitory effects on relay cells of the lateral geniculate nucleus (LGN). Corticofugal excitation was seen, if the receptive field centers (RFCs) of the VC neurons recorded at the application site were within 2.3 degrees of the RFCs of the LGN neurons under test. Inhibitory effects were seen if the RFCs of both cells were further apart up to 3.1 degrees. Glutamate application at more superficial cortical sites had no effect on LGN-neuron activity. 2. Cross-correlation analysis between spontaneous activities of simultaneously recorded VC and LGN neurons revealed excitatory cortico-geniculate connections in 18 pairs with RFCs separated by less than 1.7 degrees. In 15 pairs the peak latency of the excitation was 2--5 msec (3.4 msec in the average), 3 pairs showed long cortico-geniculate latencies (13--18 msec). The existence of a fast and slow cortico-geniculate system is suggested. 3. Inhibitory cortico-geniculate interaction was demonstrated with cross-correlation analysis in 8 pairs of which 4 had RFCs separated by more than 1.7 degrees. The onset latency of the inhibition was 2--7 msec except for 2 pairs with about 20 msec latency. 4. Most of the LGN neurons which were affected by cortical glutamate application or which showed an excitatory or inhibitory connection with a VC neurons were sustained cells, while the majority of VC neurons which were recorded in the effective glutamate application sites or which showed a significant interaction with LGN neurons in the cross-correlogram were binocularly driven and complex, with mostly large RFCs (mean diameter 3.5 degrees). They responded briskly to moving small spots as well as to moving slits. 5. It is concluded that the corticofugal excitatory effect is transmitted through monosynaptic links from VC neurons located in layer VI (complex cell) to LGN relay neurons (mostly sustained-cell) and this system is organized in a precise topographical manner. 6. In an Appendix neuron pairs which showed a positive correlation in the geniculo-cortical direction were described. The findings may support the view that complex as well as simple cells are drive monosynaptically from geniculo-cortical afferents of the sustained or transient type.

Animals↗
PubMed1975

Three principles of brain function and structure.

A large part of the presently available data in the physiology and anatomy of the nervous system is found to be consistent with three comparatively simple principles. Phrased in the terminology introduced in the paper, the first of these expresses the assumption of specificity of neuron response, the second states the biological equivalent of a maximum principle believed to govern the formation and modication of interneuronal connectivity, and the third describes the probable role of genetically determined gross anatomy in securing the groundwork for developing neurospecificity. A number of remarks are included, and an extensive discussion of the evidence behind the principles.

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