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J F Vibert

Publications and source records attributed to J F Vibert.

51 records · Page 3Linked to original sources
PubMed1979

Spike separation in multiunit records: a multivariate analysis of spike descriptive parameters.

Variables describing unit discharges from multiunit extracellular records were treated, using multivariate statistical analysis for further automatic spike separation. A spike was described by 8 parameters (3 amplitude values, 3 time values and 2 slopes). These 8 parameters were summarized by 2 new independent factors, the principal components (PC). Examination of the 2 PCs from each spike allowed the observer to determine PC families corresponding to spike populations. From these the spikes were automatically classified. PC analysis showed groups of redundant parameters. Elimination of redundancy decreased the computing time without lowering the separation efficiency of the method. Three parameters turned out to be sufficient for spike discrimination: the maximum and the minimum amplitudes and the time between these. This agrees well with the physical basis of current propagation in the conducting medium, from the firing neurone to the recording electrode.

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PubMed1979

Pentobarbitone effects on respiration related units; selective depression of bulbopontine reticular neurones.

Respiration related units (RRUs) were recorded in cats, locally anesthetized, vagotomized and immobilized, under two different experimental conditions: (1) receiving pentobarbitone intravenously at a dose inducing slight but highly significant changes in phrenic discharge; (2) unanesthetized, with a spinal section at C6. RRU characteristics were analysed in unitary volumes constituted by cubes of a matrix including the brain stem. Four parameters of RRU discharges were compared in cubes = RRU density (RRUD), RRU proportion and two indices of respiratory modulation. Cubes were sampled in: (1) dorsal and ventral bulbar respiratory nuclei, (2) pneumotaxic centre (PC), and (3) seven fields of the bulbopontine and mesencephalic reticular formation. Using the paired sample method for comparing data cube by cube in the two conditions it was shown that under pentobarbitone, RRU activity was profoundly depressed in the reticular formation surrounding dorsal and ventral bulbar respiratory nuclei, in the region bridging the gap between these and the pneumotaxic centre and extending from the pneumotaxic level to the decussation of the brachium conjunctivum. In contrast RRU activity was unchanged at the level of dorsal and ventral bulbar respiratory nuclei and in the nucleus parabrachiallis medialis (NPBM) and was increased in the Kölliker-Fuse nucleus (KF). In the mesencephalic reticular formation, increased activity was observed for non-modulated units and to a larger extent for units driven by the bulbopontine respiratory system.

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PubMed1979

Ascending projection from the respiratory centre to mesencephalon and diencephalon.

The brainstem reticular formation, subthalamus and thalamus were explored in a search for units modulated by the respiratory centre. Experiments were performed on cats under local anesthesia, in which respiratory center oscillation was independent of movement of the lungs and thorax. A large proportion of units firing tonically showed an increasing frequency, phase related to phrenic nerve activity. Respiration related units (RRUs) rostral to the pneumotaxic centre were concentrated in definite areas of the brainstem reticular formation, subthalamus and thalamus. Respiratory modulation disappeared rostral to a section performed at the ponto-mesencephalic junction.

Animals↗
PubMed1978

Estimation of the number of normal subpopulations in an heterogeneous sample and of their parameters. A recurrent method applied to neurobiology.

A method is proposed to estimate the number of subpopulations which compose a heterogeneous experimental population. The method consists of reconstructing a population sample by adding computed subpopulations, postulated to be independent. The assumption is made that each subpopulation fits a normal distribution; the method may also be generalized to other distributions laws; each subpopulation can thus be entirely defined by its mean, variance and relative weight. Recurrent adjustments of number and parameters of subpopulations are carried out in order to minimize the difference between synthetized and experimental populations. This difference was measured by the quadratic distance chi2 between the two populations. Mean, variance and weight of the computed population must then be close to those of the experimental population in order to consider the results as acceptable. This method is discussed with regard to others proposed in the literature.

Animals↗
PubMed1976

Discharge patterns of bulbo-pontine respiratory unit populations in cat.

Respiration related units (RRU) were recorded during a stratigraphic exploration of medulla and pons from the cervical junction to the caudal part of the pneumotaxic system in the semi-chronic locally anesthetized 'isolated respiratory centre' of the cat. Metal 'low impedance, capacitance compensated' microelectrodes recorded multi-unit signals from which unitary discharges were discriminated and processed by computer; it is suggested that using these techniques, the sample was a good representation of the total unit population. The phase relation to phrenic discharge was determined on cycle triggered time histograms. Of 23,000 units, 28% had a definite respiratory modulation. Examined individually, each RRU showed a stable discharge pattern corresponding to one of various respiratory types, the majority of which have been described previously. Both temporal and spatial distributions of RRU discharges were analyzed. Temporal distribution of peak firing frequencies (PFF) of 5,000 RRU sampled anatomically at random showed two main populations whose modes were observed during inspiration (I) or expiration (E). Troughs were observed in the histogram at the transition from I to E and E to I, thus indicating low probability for finding phase spanning RRU in the medulla and pons up to the pneumotaxic level. These statistical results turned out to be identical to those obtained with an a priori classification method comparable to that used in most of the previous works. In addition, the PFF distribution suggested that the E population could be further divided into 3 sub-populations whose modes fall in early, mid, and late expiration respectively. Comparison of RRU temporal distribution in two regions, one rostral, another caudal to a frontal Horsley-Clarke plane situated 3 mm in front of the obex, showed that, in the caudal region, 70% of the RRU were I units, while, in the rostral medulla and pons, equal proportions of I and E neurons were found. Temporal distribution of RRU peak frequencies was studied separately in anatomical structures where the probability of finding RRU was high. No clear correspondence between RRU types and anatomy could be found, but marked differences between structures were observed, thus suggesting nevertheless a different spatial distribution for I and E populations.

Animals↗
PubMed1976

Three dimensional representation of bulbo-pontine respiratory networks architecture from unit density maps.

Results of the preceding paper32 suggest that bulbo-pontine respiration related units (RRU) could be classed into 4 populations according to the relation of their peak firing frequency to the respiratory cycle: one inspiratory (I) and 3 expiratory (E) (early, mid and late). A further study of their spatial distribution is reported. Recorded units totalling 26,520 were distributed through a matrix of unitary cubes of which about 2,000 were found within the limits of the medulla and pons. Both percentage and density of respiratory and non-respiratory units were estimated in each cube. Statistical analysis of unit distribution showed a high probability of finding RRU in certain regions. The probability of finding I and E units in separate cubes was high, whereas there was no probability better than chance for recording one of the 3 E types separately from the 2 others. Therefore, only two populations, I and E, could be considered for spatial analysis. A thresholding technique applied to I and E unit density figures in unitary cubes demonstrated a definite limit for I and E populations. A computerized, three-dimensional (3-D) reconstruction of the outer surfaces of the I and E networks showed that half a medullary system consisted of 2 contiguous and uninterrupted columns extending from the cervical junction up to the pneumotaxic system. The main body of the I population was found in the caudal third and dorsolateral part of the bulbopontine region, while the main body of the E population was in the middle third in a ventromedial position. Both have caudal and rostral extensions that run parallel to the main axis of the brainstem and give rise to several lateral branches; these lie in close contact and interdigitate extensively, especially in the rostral third of the bulbopontine region. From the outer limits of I and E networks, a progressive increase of unit density levels was observed towards the core; it showed that inside both I and E populations, RRU aggregate into high density foci (HDF). Large HDF were found in the main body of each population. Smaller HDF were observed scattered throughout the medulla; I, and to a lesser extent E, HDF invade and surround sensory and motor nuclei and roots of the branchial nerves.

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PubMedDate not supplied

A discrete map for the dynamics of recurrent excitatory neural networks in the presence of noise.

We investigate the effect of the neuron characteristics on the behavior of a recurrent excitatory neural network model. First, we present the different types of dynamics obtained with simulations of a network of coupled excitatory spike-response neuron models placed under the influence of noise. Then, we derive a discrete map describing the dynamics of large fully connected networks. By studying the bifurcation structure of this map, we can determine for which ranges of the neuron model parameters the network will display collective oscillations or other types of dynamics.

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PubMedDate not supplied

Effects of transmission delays and noise in recurrent excitatory neural networks.

Random perturbations, referred to as noise, are omnipresent in the nervous system. We investigate how noise modifies the dynamics of the neural networks according to the delay. In this report, we examine the effect of transmission delay on both the dynamics of a single neuron receiving a recurrent excitation and the dynamics of fully interconnected excitatory networks. In the case of the single neuron with a recurrent connection, depending on the value of the delay, the discharge pattern changes from regular to multiplets. More complicated patterns appears when noise is added, and depends on both the delay and the noise intensity, but classification can be described. In certain conditions, noise reduces the synchronization, whereas in others it increases the regularity of the network activity. Finally, the same network codes the input amplitude either using mean activity amplitude coding when short delays exist, and using frequency modulation when long delays exist.

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