Temporal structure of the spike trains of neuronal pairs in the neocortex during calm wakefulness in rabbits

For revealing the conjugation of impulse activity of simultaneously recorded neurones in the visual and sensorimotor areas of rabbits neocortex, histograms were built of cross- and autocorrelation (CCH and ACH) of their discharges sequences. From successions of discharges of the visual cortex neurones, forming pairs of cells acting in correlation, spikes were singled out conjugated with neuronal discharges in the sensorimotor area, and their ACHs were built. In 77% of cases a resemblance was observed of temporal structure of conjugated discharges and real spike sequences, in 23%--there was no such resemblance. Analysis of conjugated discharges ACHs showed that they appeared predominantly periodically (87% of cases). The number of fragments with periodic discharges frequency within delta-frequency range from 3 to 4 Hz prevailed.     

Conjugation of unit activity in the visual and sensomotor areas of the rabbit neocortex during a conditioned reflex to sound and light

Conjugation of unit activity in the visual and sensorimotor neocortical areas was studied by means of histograms of cross- and autocorrelation in rabbits with conditioned reflex to light (1st group) and sound (2nd group). Relative number of neurones pairs acting in correlation in the areas remote from each other, in intersignal intervals both before and after stimuli did not differ in the 1st and 2nd groups. At the same time delays in neuronal discharges in one area after the other were different. In the 1st group animals there was a predominance of the number of visual area neurones discharging after sensorimotor with a delay up to 125 ms, in comparison with the number of sensorimotor area neurones discharging after the visual one. In the 2nd group rabbits the number of visual area neurones with such a delay of discharges after sensorimotor was less and, on the contrary, a predominance of sensorimotor area neurones was observed discharging after the visual one. The obtained results allow to suggest that neurones of the visual and sensorimotor neocortex areas form a single functional system in cases when conditioned and unconditioned stimuli are addressed to these areas and when only one of the studied areas is the projection zone for the combined stimuli. Organization of the neurones activity in systems in these two cases is different.     

Neuronal impulse trains of the visual and sensorimotor areas of the rabbit neocortex in calm wakefulness and pseudoconditioning

The conjugation of unit activity in the neocortical visual and sensorimotor areas during calm wakefulness and in intersignal intervals, in two groups of rabbits at pseudoconditioning was studied. The first group was presented in a random order with flashes and electrocutaneous stimuli, the second one--with sounds and electrocutaneous stimuli. The number of neurones pairs working in correlation during calm wakefulness is significantly less (35%) than during pseudoconditioning (49 and 50% in the first and second rabbits groups, respectively). During calm wakefulness and in both groups during pseudoconditioning, the number of pairs with delays of discharges of the visual area neurones after the sensorimotor one, and of the sensorimotor after visual up to 120 ms was equal. Comparison of the data on delayed neuronal discharges during calm wakefulness and pseudoconditioning with those obtained earlier with conditioned reflexes testifies that forestalling of visual area neuronal discharges by sensorimotor discharges is characteristic only for the activity of cortical projections of conditioned and unconditioned stimuli.     

Types of correlative relations of the neuronal impulses of the visual and sensomotor areas of the neocortex in the rabbit

Neuronal activity of the visual and sensorimotor cortical areas was simultaneously recorded in intersignal intervals in rabbits with conditioned reflexes to light and sound. ES-1020 computer built cross-correlation (CCH) and autocorrelation (ACH) histograms of impulse activity of the se neurones. Analysis of CCH form, built with a bin of 2 ms gave no convincing proofs of the presence of synaptic connections between neurone of the visual and sensorimotor cortical areas and of influences from a common source with few switchings on interneurones. Analysis of CCH built with bins of 10 and 30 ms, allowed to single out primary and secondary peaks and troughs. Wide primary peaks with the base covering the beginning of the coordinates, were met in 51.9% of cases; wide peaks, greatly shifted relatively to the coordinates beginning,--in 40.9% and trough--in 7.2% of cases. Secondary peaks did not always reproduce the ACH form of impulses trains of recorded neurones. The CCH analysis allowed to suggest two basic mechanisms, eliciting the correlated discharges--action of common input and influence of the neurones of one area on the other through a number of interneurones. It was not always possible to separate these two cases by means of CCH. In a number of cases, a more complicated character of neurones interaction could be suggested.     

Interaction between neurons of the visual and sensomotor areas of the neocortex during elaboration and extinction of a conditioned defense reflex

Cooperation in activities of pairs of neurones situated in projection cortical areas of conditioned and unconditioned stimuli was studied in rabbits during intertrial intervals at different stages of elaboration and extinction of conditioned defensive response by means of auto- and crosscorrelation analysis of impulse fluxes. At the stage of generalization the number of pairs of neurones discharging in correlation was shown to increase a little (64 per cent) in comparison to that at the initial stage of conditioning (50 per cent) and pseudoconditioning (54 per cent). At the stage of stabilization and during extinction the number of pairs of neurones discharging in correlation decreased correspondingly to 34 and 32 per cent. Parallel analysis of correlation in neuronal discharges and simultaneously recorded electroencephalogram allowed to suppose that excitatory synchronizing influences and inhibitory cortical system play a great part in synchronization of activities of cortical neurones. Participation of these two systems is not the same at different stages of conditioning and extinction.     

Effects of acetylcholine and cholinergic transmission blockers on neuronal spike activity in the cat motor cortex associated with conditioned reflex

The effects of direct application of acetylcholine (ACh) and m- and n-cholinoreceptor blockers on test cells were investigated in waking cats having developed instrumental lever-pressing conditioned reflex. Changes were recorded in both spontaneous and invoked firing activity in a functionally homogeneous group of motor cortex cells, in which increased discharge rate usually preceded the start of conditioned reflex movements. It was found, however, that ACh increased spontaneous activity considerably in some of the neurons tested and reduced it moderately in others. Atropine sharply reduced background activity in cortical neurons while preserving spike response to presentation of a conditioned stimulus and n-cholino-blockers such as hexonium and (occasionally) tubocurarine inhibited spike response produced by conditioned stimuli; background activity was slightly inhibited by hexonium and reinforced by tubocurarine. It was concluded that ACh put out by cholinergic fibers helps to maintain background firing activity level in cortical neurons under naturally occurring conditions, acting via m-cholinoreceptors, whereas factors influencing generation of spike discharges associated with performance of conditioned reflex movements are mediated by n-cholinoreceptors.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 579–589, September–October, 1989.     

Inhibitory influence of supplementary extraneous stimulation upon neuronal responses in the sensorimotor cortex of the cat during a conditioned reflex

Using alert rabbits trained to perform placing movements in response to a sound click, we investigated impulse responses (IR) of neurons of the somatosensory cortex preceding realization of the reflex by 50–150 msec. When a brief extraneous stimulation (light flashes, audible tone, electrical stimulation of a limb) was applied after initiation of the reflex, learned movements with the earlier behavioral parameters (latent periods and duration) were maintained. However, the IR of neurons to the presentation of a conditioned stimulus (CS) was of lesser intensity and arose 50–250 msec later. A constant extraneous stimulation (an audible tone, a forced stream of air upon the muzzle) or a decrease in the intensity of the CS administered to the threshold of hearing resulted in similar changes in the neuronal responses upon the application of the CS, but the parameters of the learned movements were maintained. We suggest that the cause of these changes in neuronal responses is increased exteroceptive attention to extraneous stimulation to additional extraneous stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 174–181, March–April, 1991.     

Conjugation of the neuronal impulse activity in the rabbit neocortex during self stimulation of the lateral hypothalamus

Correlation of impulse activity of visual and sensorimotor neurons of both hemispheres in 10-s interval after self-stimulation of the right and left lateral hypothalamus was studied by plotting cross- and autocorrelation histograms. The number of cell pairs, in which sensorimotor neurons discharged after visual ones, increased after self-stimulation (from 24 +/- 6 to 44 +/- 7%). Frequencies of the alpha- and theta-range in crosscorrelograms increased; the alpha frequency increased mainly in the right hemisphere, while the theta frequency increased in the left hemisphere. The interhemispheric asymmetry in the interaction between cortical neurons was not associated with the side of hypothalamic stimulation.     

Correlation of the neuronal impulse activity of different areas of the neocortex in rabbits in the switching of positive and inhibitory conditioned reflexes

By cross-correlation method conjugation in impulse activity of pairs of simultaneously recorded units in the visual and sensorimotor areas of the neocortex (representations of the conditioned and unconditioned stimuli) was studied during the switching of defensive positive and inhibitory reflexes in rabbits. 30-second fragments of impulse activity were analyzed in intervals before and after three presentations of positive and inhibitory conditioned stimuli (CS). The activity of single pairs of units in the process of stimuli presentation was characterized by instability. Only in 29% of 51 units' pairs the presence or absence of correlation between their discharges was stable. Analysis of activity of 75 pairs of units showed differences in impulse activity in inhibitory and positive tonic reflexes. The number of pairs of correlated units in about 30 s after inhibitory CS decreased (27%) in comparison with the interval before its action (52%). In the inhibitory tonic conditioned reflex, temporal intervals of discharges of one unit correlated with discharges of the second unit undergo changes. The obtained results testify that such parameter as the number of pairs of units with correlated activity in intersignal time interval is very important for the realization of motor reaction to conditioned stimuli.     

Elimination of response latency variability in neuronal spike trains

 Neuronal activity in the mammalian cortex exhibits a considerable amount of trial-by-trial variability. This may be reflected by the magnitude of the activity as well as by the response latency with respect to an external event, such as the onset of a sensory stimulus, or a behavioral event. Here we present a novel nonparametric method for estimating trial-by-trial differences in response latency from neuronal spike trains. The method makes use of the dynamic rate profile for each single trial and maximizes their total pairwise correlation by appropriately shifting all trials in time. The result is a new alignment of trials that largely eliminates the variability in response latency and provides a new internal trigger that is independent of experiment time. To calibrate the method, we simulated spike trains based on stochastic point processes using a parametric model for phasic response profiles. We illustrate the method by an application to simultaneous recordings from a pair of neurons in the motor cortex of a behaving monkey. It is demonstrated how the method can be used to study the temporal relation of the neuronal response to the experiment, to investigate whether neurons share the same dynamics, and to improve spike correlation analysis. Differences between this and other previously published methods are discussed. Received: 8 April 2002 / Accepted: 26 November 2002 / Published online: 7 April 2003 Correspondence to: Stefan Rotter (e-mail: rotter@biologie.uni-freiburg.de), Tel.: +49-761-2032862, Fax: +49-761-2032860 Acknowledgements. We are grateful to Alexa Riehle for providing us with the monkey data and for valuable discussions. We also thank Felix Kümmell, Hiroyuki Nakahara, and Shun-ichi Amari for helpful discussions. Partial funding was received by the Deutsche Forschungsgemeinschaft (DFG, SFB 505) and the German-Israeli Foundation (GIF). Additional support was provided by the RIKEN Brain Science Institute.     

Role of a goal in determining neuronal activity of the motor and visual areas of the rabbit cortex

In experiments on alert rabbits neuronal activity of the motor and visual cortical areas was studied in behavioural acts (BA) of grasping of a piece of plastics (P) and carrot (C) from consequently presented cups of the feeder; the animal had an opportunity to seize a C piece only after grasping and taking away from the previous cup the P piece. "Visual environment" in which BA were realized were identical; P and C pieces were identical in form and visual characteristics. Records were made of unit activity (201 cells), animal's movements (photoelectric method), EMG of the m. masseter; in parallel videorecords of behaviour were carried out. BA of P and C pieces grasping were identical in electromyo- and actographic characteristics; motor composition of these BA did not differ. 61 neurones were activated in both BA, 5--only in BA of P piece grasping, 22--only in BA of C piece grasping, i. e. 30% of neurones were activated only in one of the compared BA. Characteristics of activations, appearing in both acts could be significantly different: different frequency, connection with different stages of the compared BA. The obtained data are determined by changes of the motor and receptive fields of neurones in one BA in comparison to another, and are considered as an evidence supporting the suggestion that appearance of cortical neurones' activations in behaviour depends on BA goal and is not strictly determined by the parameters of movements and environment.     

Note on the coefficient of variations of neuronal spike trains

It is known that many neurons in the brain show spike trains with a coefficient of variation (CV) of the interspike times of approximately 1, thus resembling the properties of Poisson spike trains. Computational studies have been able to reproduce this phenomenon. However, the underlying models were too complex to be examined analytically. In this paper, we offer a simple model that shows the same effect but is accessible to an analytic treatment. The model is a random walk model with a reflecting barrier; we give explicit formulas for the CV in the regime of excess inhibition. We also analyze the effect of probabilistic synapses in our model and show that it resembles previous findings that were obtained by simulation.     

Postsynaptic neuronal response of a cat sensorimotor cortex during evoked and self-sustained rhythmic "spike and wave" activity

Intracellular correlates of complex sets of rhythmic cortical "spike and wave" potentials evoked in sensorimotor cortex and of self-sustained rhythmic "spike and wave" activity were examined during acute experiments on cats immobilized by myorelaxants. Rhythmic spike-wave activity was produced by stimulating the thalamic relay (ventroposterolateral) nucleus (VPLN) at the rate of 3 Hz; self-sustained afterdischarges were recorded following 8–14 Hz stimulation of the same nucleus. Components of the spike and wave afterdischarge mainly correspond to the paroxysmal depolarizing shifts of the membrane potential of cortical neurons in length. After cessation of self-sustained spike and wave activity, prolonged hyperpolarization accompanied by inhibition of spike discharges and subsequent reinstatement of background activity was observed in cortical neurons. It is postulated that the negative slow wave of induced spike and wave activity as well as slow negative potentials of direct cortical and primary response reflect IPSP in more deep-lying areas of the cell bodies, while the wave of self-sustained rhythmic activity is due to paroxysmal depolarizing shifts in the membrane potential of cortical neurons.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 298–306, May–June, 1986.     

Dynamics of driven rhythm in neuronal assemblies in sensorimotor and visual cerebral cortices in rabbit

Coincident activity of pairs of neurons in the sensorimotor and visual areas of the cerebral cortex was studied in naive, learning, and trained rabbits during the formation of a hidden excitation focus in their central nervous system (a defensive dominanta) of the rhythmic nature. In the trained rabbits (as compared to the naive animals), percent of neuronal pairs (both neighboring and distant) in whose coincident activity the rhythm of stimulation prevailed was higher. In the visual cortex, percent of such pairs was significantly higher only for the distant neurons. Analysis of interaction between neurons in the visual and sensorimotor cortices revealed increasing the number of neuronal pairs with the driven rhythm while training. Such an increase was observed when both sensorimotor and visual neurons were considered as leading.