Correlation between activities of neurons of sensorimotor and visual cortices after forming a hidden focus of excitation (defensive dominanta) in cortical representation of a forelimb in rabbits

The interaction between neurons of sensorimotor and visual cortices was investigated by cross-correlation analysis. In this interaction, we examined the role of sensorimotor neurons responding to light. In rabbits with a hidden focus of excitation, neurons of the sensorimotor cortex responding to light significantly more often formed correlation joints with cells of the visual cortex than neurons not responding to light. On the other hand, neurons of the visual cortex significantly more often formed correlation joints with neurons of the sensorimotor cortex not responding to light.     

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.     

Cortical network activity before behavioral reaction and before its omission in rabbits with defensive dominanta

Defensive dominanta was formed in rabbit CNS. Activity of the cortical neuronal network was investigated in these rabbits in the state of quiet wakefulness and in the intervals between the presentations of testing stimulus (light flashes). Statistical analysis of spike trains revealed some distinctions in neuronal functional organizations in the excitation focus (sensorimotor cortex) and in the visual cortex in the states of quiet wakefulness, before the movement of the paw, and before the omission of the reaction. The evidence of different roles in the network activity of sensorimotor neurons that responded and not responded to light was obtained.     

The morphofunctional characteristics of the neurons in the sensorimotor cortex of old rabbits during the trace assimilation of rhythm]

Extracellular neuronal activity was recorded from 460 neurons from alert young (5-7 months), middle-aged (54-65 months) and old (66-85 months) rabbits. Trace rhythmic activity of sensorimotor cortical neurons was examined after long-lasting (10-20 min) rhythmic (0.5-2 Hz) electrocutaneous stimulation of the contralateral forelimb. Spectral analysis of spike activity showed age-related differences in capability of producing a rhythm of previous stimulation in spontaneous neuronal activity. In young animals propriate rhythmic fluctuations of firing rate appeared after the first or second sessions of stimulations (on the first experimental day), in middle-aged ones--after 2-4 sessions (on the second or third days); cortical neurons in old rabbits did not exhibit trace rhythmic activity. Significant morphological changes in glial and neuronal cells were observed in sensorimotor cortex of old rabbits. It is proposed that morphological deteriorations may be the reason of the impairement of trace processes during aging.     

Effect of "animal hypnosis" on the rhythmic defensive dominanta

A defensive dominanta (stationary excitation focus) in the sensorimotor cortex of rabbits was formed by rhythmical electrodermal paw stimulation with the frequency of 0.5 Hz. After cessation of the stimulation, the state of hidden excitation was tested with acoustic stimuli, in response to which nonrhythmic activity of leg muscles increased or the leg rhythmically startled with the frequency close to that of the electrodermal stimulation. After conducting a routine hypnotizing procedure, the incidence of the rhythmic responses to testing stimulation increased, while the incidence of nonrhythmic responses decreased.     

Effects of stimulus duration on neuronal response properties in the somatosensory cortex of the star-nosed mole

Star-nosed moles have a series of mechanosensory appendages surrounding each nostril. Each appendage is covered with sensory organs (Eimer's organs) containing both rapidly adapting and slowly adapting mechanoreceptors and each appendage is represented in primary somatosensory cortex (S1) by a single cortical module. When the skin surface of an appendage is depressed, neurons in the corresponding module in S1 respond in either a transient or sustained fashion. The aim of this study was to characterize and compare the responses of these two classes of neurons to both short (5 or 20 ms) and long (500 ms) mechanosensory stimulation. Activity from neurons in the representation of appendage 11, the somatosensory fovea, was recorded while delivering mechanosensory stimuli to the corresponding skin surface. Transient and sustained neurons had different levels of spontaneous activity and different responses to both short and long mechanosensory stimulation. Neurons with sustained responses had a significantly higher spontaneous firing rate than neurons with transient responses. Transient neurons responded to a 5 ms stimulus with excitation followed by suppression of discharge whereas sustained neurons did not exhibit post-excitatory suppression. Rather, responses of sustained neurons to 5 ms stimuli lasted several hundred milliseconds. Consequently sustained responses contained significantly more spikes than transient responses. These experiments suggest contact to the appendages causes two distinct firing patterns in cortex regardless of the duration of the stimulus. The sustained and transient responses could reflect either the activity of fundamentally different classes of neurons or activity in distinct subcortical and cortical networks.     

Estimation of the interaction strength in the rabbit sensomotor cortex neurons before and after formation of the defense focus

The strength of interaction between neurons in the sensorimotor cortex of rabbits was compared before and after the formation of a hidden excitatory focus (dominant) in this cortical area. In control experiments the interactions between the neurons was significantly stronger in cases when the influence of the neurons with higher spike amplitude on the neurons generating lower-amplitude pulses was assessed. This difference disappeared in the dominant focus.     

Cortical Influences on Neurons of the Lateral Reticular Nucleus Responding to Noxious Stimuli

The effect of frontoparietal sensorimotor (FPSM) cortex stimulation on both the spontaneous and the noxious evoked activity of neurons in the lateral reticular nucleus (LRN) was tested in barbiturate-anesthetized rats. Ninety-three LRN neurons that responded to a noxious heat stimulus (HS) were recorded (72% antidromically fired from the cerebellum). Of these, 66 neurons altered their spontaneous firing rates in response to cortical stimulation. Two patterns of responses were found: either an excitation followed by a suppression of spontaneous activity (52 neurons), or a pure suppression of spontaneous activity lasting 50-400 msec (14 neurons). In 46 of these neurons, it was found that cortical stimulation reduced HS-evoked activity to near the baseline level. Furthermore, it was found that when applied after a prolonged cortical stimulation, the HS was ineffective. It is concluded that FPSM cortex can influence nociceptive information in LRN neurons that respond to its stimulation, possibly interfering with the mechanisms underlying stimulation-produced analgesia (SPA). In this context, it is proposed that the cortex can modulate the activity of LRN neurons that activate, through local loops, a descending antinociceptive system and also a separate projection system to the cerebellum.     

Cortical influences on neurons of the lateral reticular nucleus responding to noxious stimuli

The effect of frontoparietal sensorimotor (FPSM) cortex stimulation on both the spontaneous and the noxious evoked activity of neurons in the lateral reticular nucleus (LRN) was tested in barbiturate-anesthetized rats. Ninety-three LRN neurons that responded to a noxious heat stimulus (HS) were recorded (72% antidromically fired from the cerebellum). Of these, 66 neurons altered their spontaneous firing rates in response to cortical stimulation. Two patterns of responses were found: either an excitation followed by a suppression of spontaneous activity (52 neurons), or a pure suppression of spontaneous activity lasting 50-400 msec (14 neurons). In 46 of these neurons, it was found that cortical stimulation reduced HS-evoked activity to near the baseline level. Furthermore, it was found that when applied after a prolonged cortical stimulation, the HS was ineffective. It is concluded that FPSM cortex can influence nociceptive information in LRN neurons that respond to its stimulation, possibly interfering with the mechanisms underlying stimulation-produced analgesia (SPA). In this context, it is proposed that the cortex can modulate the activity of LRN neurons that activate, through local loops, a descending antinociceptive system and also a separate projection system to the cerebellum.     

Changes in the activity of cells in the lateral geniculate nucleus by stimulation of the abducens nucleus area in rabbits

These investigations are aimed at studying the influence of the electrical stimulation of the VIth nucleus (abducens nucleus) on responses of lateral geniculate cells in rabbits. The animals were prepared in the usual fashion for single cell recordings at the lateral geniculate nucleus (LGN). Results show that: Electrical stimulation of the VIth nucleus always produced excitatory discharges whose latency varied from 30 to 400 ms. Interestingly, an electrical pulse applied to the abducens nucleus was capable of enhancing the light-evoked responses without altering the spontaneous rate of firing. It thus seems that the ascending influence of the VIth nucleus manifests itself when it coincides with light responses. Most cells which were sensitive to electrical activation of the abducens nucleus had their receptive field located peripherally (greater than 50 degrees). Histological reconstructions of recording electrode tracts suggest that cells which responded to electrical stimulation were located in a narrow band lying dorsally relative to the LGN. This area can be paralleled with the perigeniculate area observed in other mammals, although not identified in rabbits. It is suggested that these extraretinal impulses which reach the LGN and emerge from an area surrounding the VIth nucleus are associated with corollary discharges.     

Corticofugal postsynaptic influences on red nucleus neurons

The responses of red nucleus neurons to stimulation of the sensorimotor cortex was studied on nembutal-anesthetized cats. Most of the rubrospinal neurons were identified according to their antidromic activation. Stimulation of the sensorimotor cortex was shown to evoke in the red nucleus neurons monosynaptic excitatory potentials with a latency of 1.85 msec, polysynaptic excitatory potentials (EPSP), and inhibitory postsynaptic potentials (IPSP) with a latency of 9–24 msec. The EPSP often produced spikes. The probability of generation of spreading excitation is greater with motor cortex stimulation. The monosynaptic EPSP are assumed to arise under the influence of the impulses arriving over the corticorubral neurons as a result of excitation of axodendritic synapses. The radial type of branching of red nucleus neurons facilitates the transition from electrotonically spreading local depolarization to an action potential triggered by the initial axonal segment. Polysynaptic EPSP and IPSP seem to be a result of activation of fast pyramidal neurons whose axon collaterals are connected via interneurons with the soma of the red nucleus neurons.L. A. Orbeli Institute of Physiology of the Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 43–51, January–February, 1971.     

The transmission of coded information over neuronal systems exemplified by the motor rhythmic dominant

Functional organization of neurons in rabbit's sensorimotor cortex was studied before and within several days after formation of the rhythmical dominant focus. Functional reorganization of neurons in cortical microareas took place during actualization of the dominant. The number of functional interneuronal relations within neuronal pairs of a certain type could be increased in comparison with the control values and decreased within pairs of another type. As a result, the total percent of the interneuronal correlations in cortical microareas in the control animals and rabbits with the acting dominant was approximately equal. The total percent of correlations between neurons of the adjacent cortical areas during the actualization of the dominant was significantly higher than in the control due to increased number of correlations with participation of small and medium-sized neurons. A possibility of information circulation about the "stimulus image" in the closed chain of neurons was exemplified by the real micronetwork. The data suggest the reverberation of encoded information between adjacent microareas of the sensorimotor cortex within several days after application of the stimulus, which has formed the excitation focus.     

Cholinergic sensitivity as an index of the functional differences in cortical neurons in young and old rabbits]

Acetylcholine-sensitivity of motor cortex neurons was studied in the young and old rabbits. Muscarinic-type excitation in the neurons of old animals was revealed twice less frequently compared to the young ones. The age-related fall in the number of cholinoceptive neurons may be due to general decrease of neuronal activation in the motor cortex during aging. Changes in functional properties of motor cortex neurons with age may have a result that firing rate of movement related neurons becomes insufficient for the effective control of motor function.     

Neuron activities of the motor cortex during conditioned eye blink reflex in rabbits (author's transl)]

Effects of the tone (CS) on neurons of the motor cortex were investigated in naive, pseudoconditioned, and conditioned rabbits. Conditioning to eye blink reflex was made by a combination of CS and air puff (US). Effects of electrical stimulation of the subcortical structures were also observed on the cortical neurons associated with the conditioned reflex. The results were as follows. (1) Proportion of neurons which significantly increased the firing rate in response to the CS, type E, was higher in the conditioned group than in other two groups. On the other hand, no group difference was found in the proportion of neurons which significantly decreased the firing rate to the stimulus, type I. (2) Most of the type E neurons in the conditioned rabbits began to fire at latencies of about 50 to 100 msec after the CS, preceding about 200 msec to the appearance of the peripheral conditioned responses (EMG). (3) Most of the type E neurons in the conditioned animals were more easily affected by stimulation of the medial geniculate body and the brain stem reticular formation. Based on the results mentioned above, it is concluded that in the rabbits conditioned to the eye blink reflex, excitability of neurons in the motor cortex is enhanced by the tone (CS), and by electrical stimulation to the medial geniculate body and the brain stem reticular formation.     

Modulation of the neuronal activity and evoked potentials of the cerebral cortex by stimulation of the dorsal hippocampus]

In experiments on alert rabbits high frequency stimulation of the CA1 field of the dorsal hippocampus reduced the peak latency of the main negative component of the evoked potential (EP) to a light flash in the sensorimotor and occipital tests areas of the cerebral cortex. A single stimulation of the same part of the hippocampus resulted in a gradually developing facilitation of secondary negativity of the EP 5th component, predominantly in the sensorimotor cortex. Investigation of neuronal responses in the same cortical areas to a stimulation of the CA1 field with different parameters has shown that the effects of EP modulation are due to dynamic reorganizations of cortical neuronal activity.     

Nuclear and cytoplasmic RNA in visual cortex neurons of adult rats following visual deprivation and photic stimulation

It has been shown by two-wavelength cytospectrophotometry of gallocyanin-chrome alum-stained sections that visual deprivation in adult rats kept in a complete darkness for 30 days resulted in an accumulation of cytoplasmic RNA by layer V neurons of the visual cerebral cortex and by the cells of the perineuronal neuroglia of this layer. The nuclear RNA content remained unchanged. Stimulation of intact rats with a flickering or constant light induced an increase in the cytoplasmic RNA in these neurons rather than in the nuclear RNA as well as in RNA in their glial satellite cells. Similar light stimulation of the deprived animals gave rise to a complete return of the neuronal RNA to normal with only a slight decrease in the deprivation-induced RNA accumulation by the neuroglial cells. Neither visual deprivation nor light stimulation affected the RNA content in the neurons and neuroglia of layer V of the motor cerebral cortex. Compartmentation of RNA metabolism within the neuronal-neuroglial unit is discussed.     

Correlated activity of neurons in the sensorimotor cortex of rabbits in the state of defensive dominanta and "animal hypnosis"

A hidden excitation focus (dominanta focus) was produced in the rabbit's CNS by threshold electrical stimulation of the left forelimb with the frequency of 0.5 Hz. As a rule, after the formation of the focus, pairs of neurons with prevailing two-second rhythm in their correlated activity were revealed both in the left and right sensorimotor cortices (with equal probabilities 29.3 and 32.4%, respectively). After "animal hypnosis" induction, the total percent of neuronal pairs with the prevalent dominanta-induced rhythm decreased significantly only in the right hemisphere (21%). After the termination of the "animal hypnosis" state, percent of neuronal pairs in the right cortex with prevailing two-second rhythm significantly increasead if the neurons in a pair were neighboring and decreased if they were remote from each other. Similar changes after the hypnotization were not found in the left cortex. Analysis of correlated activity of neuronal pairs with regard to amplitude characteristics showed that for both the right and left hemispheres, the prevalence of the two-second rhythm was more frequently observed in crosscorrelation histograms constructed regarding discharges of neurons with the lowest spike amplitude (in the right hemisphere) or the lowest and mean amplitudes (in the left hemisphere) selected from multiunit records.     

Masking effect of different durations of forward masker sound on acoustical responses of mouse inferior collicular neurons to probe sound

To study the effects of different durations of forward masker sound on neuronal firing and rate-intensity function(RIF)of mouse inferior collicular(IC)neurons,a tone relative to 5 dB above the minimum threshold(re MT+5 dB)of the best frequency of recorded neurons was used as forward masker sound under free field stimulation condition.The masker durations used were 40,60,80,and 100 ms.Results showed that as masker duration was increased,inhibition in neuronal firing was enhanced(P＜0.0001,n=41)and the latency of neurons was lengthened(P＜0.01,n=41).In addition,among 41 inhibited IC neurons,90.2%(37/41)exhibited narrowed dynamic range(DR)when masker sound duration was increased(P＜0.0001),whereas the DR of 9.8%(4/41)became wider.These data suggest that masking effects of different durations of forward masker sound might be correlated with the amplitude and duration of inhibitory input to IC neurons elicited by the masker sound.     

Changes in potentiation and timing of sensorimotor transmission after adaptation of a postsynaptic transient outward current in a simulated cortical neuron

How adaptation of a postsynaptic transient outward current might affect the efficacy of sensorimotor transmission was investigated. The transmission signals that were studied were a 5 ms conditioned stimulus (CS) and a 60 ms US drawn from intracellularly recorded, depolarizing postsynaptic potentials (PSPs) elicited in pyramidal neurons of the cat motor cortex by a click CS and a glabella tap US, respectively. SPICE, a program used to analyze electrical circuits, was used to simulate the cortical neuron containing the adaptive outward current. Changes in the magnitude and latency of rise to firing threshold of the PSPs were compared i) after presynaptic augmentation of a CS input in the absence of an adaptive postsynaptic current and ii) after decreasing the magnitude of an adaptive postsynaptic current that was rapidly activated by depolarization. Effects of short (6 ms) and long (24 ms) inactivation time constants of the postsynaptic current were also studied. In both presynaptic adaptation and postsynaptic adaptation, the potentiation of the magnitude of the CS-induced PSP was similar, with the latency to threshold being reduced by < or = 1 ms in both cases. The effects on the US PSP differed. Presynaptic adaptation affecting the CS had no effect on the US. Adaptation of the CS by a postsynaptic outward current with a 6 ms inactivation time constant, reduced the latency to threshold of an EPSP from a nearby US synapse by up to 6 ms by augmenting the initial portion of the slowly rising US-induced PSP. Adaptation of a postsynaptic current with a 24 ms inactivation time constant reduced the latency of response to the US PSP by up to 16 ms. When the US synapse was relocated to the soma, the reduction in US latency caused by adaptation of the outward current at the CS synapse was reduced by up to one half. The latency of slowly rising components of integrated synaptic responses to compound CSs of > 5 ms duration from multiple synaptic inputs would be expected to show reductions corresponding to those of the US. We conclude that potentiation of synaptic transmission by adaptation of a postsynaptic outward current can result in reductions of latency of sensorimotor transmission that can significantly affect the timing and accuracy of controlled motor tasks. These effects depend significantly on the locations of the synaptic inputs within the cell.     

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.