Responses of sensorimotor and visual cortical neurons to light in rabbits with a hidden focus of excitation in the CNS (defensive dominanta)

In the sensorimotor cortex of rabbits with a hidden focus of excitation in the CNS, the firing rate of neurons that responded to light was significantly lower (p = 0.01) than the firing rate of neurons that did not respond to light. The same phenomenon was observed in the visual cortex of intact rabbits. Both in intact rabbits and animals with the hidden focus of excitation, 36% of neurons in the sensorimotor responded to a nonspecific for them light stimulation. In the sensorimotor cortex of rabbits with the hidden focus of excitation, more (p = 0.01) neurons responded to light with the latency lower that 100 ms and less (p = 0.02) neurons responded to light with the latency from 200 to 300 ms as compared to intact animals. In the visual cortex of rabbits with the hidden excitation focus, less (p = 0.01) neurons responded to light stimulation with the latency from 50 to 100 ms as compared to intact rabbits.     

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.     

Dynamics of neuronal activity in the lateral preoptic area of hypothalamus in the course of sleep-waking cycle

Frequency and patterns of activity of 106 neurons in the lateral preoptic area of unanesthetized cats were studied under conditions of indolent head fixation. It was shown that this structure contains two somnogenic neuronal populations with different functions. Neurons increasing their discharge frequency during transition from active to quiet wakefulness and subsequent sleep development to the point of phasic stage of paradoxical sleep development are considered as elements of an anti-waking system, which is involved in the mechanisms of sleep onset and deepening by means of inactivation of the arousal system. Neurons displaying the highest firing rates during light slow-wave sleep and synchronization of discharges with sleep spindles are considered as elements of a slow-wave sleep network.     

The influence of glycine on EEG parameters and sensorimotor activity in normal and alcoholic subjects

The influence of a pharmaceutical preparation of glycine on the EEG and the quality of sensorimotor activity of healthy subjects and alcoholics was studied during the performance of a test on pursuing tracking. Subjects with left-sided dominance of spatial synchronization of cortical biopotentials in the posterofron-totemporal areas under conditions of quiet wakefulness with open eyes were found to have an advantage in performing this kind of activity. Glycine normalized pathological changes of cortical activity and, under certain conditions, improved sensorimotor parameters of operator activity.     

Function of the superior colliculi of the corpora quadrigemina during creation of a local focus of increased excitability in the mesencephalic reticular formation and sensomotor cortex

In chronic experiments on waking rabbits, the foci of heightened excitability in the sensorimotor cortex and mesencephalic reticular formation affected in a similar way the background neuronal activity in the superior colliculi and that evoked by light stimuli. The effect was manifested in elimination of inhibitory pauses in the neuronal response to light stimulus and in a general increase of discharge frequency. Similarity of the cortical and reticular influences is due to their possible mediation by the same collicular interneurones participating in inhibitory pauses formation in the process of backward inhibition. Increased neuronal activity in the superior colliculi under the action of local foci in the sensorimotor cortex and mesencephalic reticular formation correlated with appearance of forelimb motor reaction to isolated light stimulus testifying to a formation of a functional connection between the visual and motor analyzers. Possible role of the superior colliculi in this process and their participation in the formation of a visually controlled reaction is discussed.     

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.     

Cortical Presynaptic Control of Dorsal Horn C–Afferents in the Rat

Lamina 5 sensorimotor cortex pyramidal neurons project to the spinal cord, participating in the modulation of several modalities of information transmission. A well-studied mechanism by which the corticospinal projection modulates sensory information is primary afferent depolarization, which has been characterized in fast muscular and cutaneous, but not in slow-conducting nociceptive skin afferents. Here we investigated whether the inhibition of nociceptive sensory information, produced by activation of the sensorimotor cortex, involves a direct presynaptic modulation of C primary afferents. In anaesthetized male Wistar rats, we analyzed the effects of sensorimotor cortex activation on post tetanic potentiation (PTP) and the paired pulse ratio (PPR) of dorsal horn field potentials evoked by C–fiber stimulation in the sural (SU) and sciatic (SC) nerves. We also explored the time course of the excitability changes in nociceptive afferents produced by cortical stimulation. We observed that the development of PTP was completely blocked when C-fiber tetanic stimulation was paired with cortex stimulation. In addition, sensorimotor cortex activation by topical administration of bicuculline (BIC) produced a reduction in the amplitude of C–fiber responses, as well as an increase in the PPR. Furthermore, increases in the intraspinal excitability of slow-conducting fiber terminals, produced by sensorimotor cortex stimulation, were indicative of primary afferent depolarization. Topical administration of BIC in the spinal cord blocked the inhibition of C–fiber neuronal responses produced by cortical stimulation. Dorsal horn neurons responding to sensorimotor cortex stimulation also exhibited a peripheral receptive field and responded to stimulation of fast cutaneous myelinated fibers. Our results suggest that corticospinal inhibition of nociceptive responses is due in part to a modulation of the excitability of primary C–fibers by means of GABAergic inhibitory interneurons.     

Methods for predicting cortical UP and DOWN states from the phase of deep layer local field potentials

During anesthesia, slow-wave sleep and quiet wakefulness, neuronal membrane potentials collectively switch between de- and hyperpolarized levels, the cortical UP and DOWN states. Previous studies have shown that these cortical UP/DOWN states affect the excitability of individual neurons in response to sensory stimuli, indicating that a significant amount of the trial-to-trial variability in neuronal responses can be attributed to ongoing fluctuations in network activity. However, as intracellular recordings are frequently not available, it is important to be able to estimate their occurrence purely from extracellular data. Here, we combine in vivo whole cell recordings from single neurons with multi-site extracellular microelectrode recordings, to quantify the performance of various approaches to predicting UP/DOWN states from the deep-layer local field potential (LFP). We find that UP/DOWN states in deep cortical layers of rat primary auditory cortex (A1) are predictable from the phase of LFP at low frequencies (< 4 Hz), and that the likelihood of a given state varies sinusoidally with the phase of LFP at these frequencies. We introduce a novel method of detecting cortical state by combining information concerning the phase of the LFP and ongoing multi-unit activity.     

Behavioural state influences the cardiovascular response to haemorrhage in lambs

We investigated the effect of behavioural state on the cardiovascular response to an acute venous haemorrhage in 7 lambs aged 13 to 19 days. Each lamb had previously been anaesthetized and instrumented for measurements of electrocorticogram, electro-oculogram, nuchal and diaphragm electromyograms, pulmonary blood flow (electromagnetic flow transducer), aortic and right atrial blood pressures. The lambs were allowed to recover from surgery at least three days before they were studied. Measurements were made during a 1-minute control period and during a 1-minute experimental period that followed a 10 ml/kg body weight haemorrhage during quiet wakefulness, quiet sleep and active sleep; the haemorrhage took approximately 30s. Haemorrhage produced similar decreases in right atrial pressure and pulmonary blood flow during the three behavioural states. However, mean aortic pressure decreased more following haemorrhage during active sleep than during quiet sleep or quiet wakefulness. These results provide evidence that reflex control of the peripheral circulation is altered during active sleep compared to quiet sleep and quiet wakefulness in lambs.     

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.     

Impulsation of hypothalamic and amygdalar neurons in bilateral derivations in the state of food motivation

The character of impulsation of single neurons in the lateral hypothalamic and amygdalar central nucleus of rabbits recorded in bilateral derivations during quiet wakefulness, after 24-h food deprivation, and after satiation was studied by plotting autocorrelation histograms and by counting the mean frequency of discharges. During the transition from hunger to satiation, the character of impulsation of neurons in hypothalamus and amygdala changed in different ways: (1) a greater number of hypothalamic than amygdalar neurons changed their mean discharge frequency (85 versus 56%, respectively); (2) in hunger, the number of hypothalamic neurons with delta-frequency oscillations decreased as compared to quiet wakefulness and satiation, and in the amyglala the number of neurons with beta2-frequency oscillations increased; (3) in hunger, the number of hypothalamic neurons with bursting and periodic discharges decreased and the number of amygdalar neurons with equiprobabilistic discharges increased. During state alternation (according to the autocorrelation histograms) the strongest changes in the character of neuronal discharges took place in the left hypothalamus and left amygdala. The maximum differences in neuronal impulsation between the left and right hypothalamus were observed in the state of hunger and between the left and right amygdala, after satiation.     

Ensemble activity of neurons in the visual, frontal, and sensorimotor cortices and dorsal striatum during actualization of behavioral program under conditions of strategy choice

Unit and network activity of neurons in the visual, sensorimotor, and frontal cortical areas and dorsal striatum was investigated in cats under conditions of choice of the reinforcement value depending on its delay. The animals did not differ from each other in behavior. After immediate or delayed responses cats got low- or highly-valuable reinforcement, respectively. Single-unit activity in the visual and sensorimotor cortical areas and dorsal striatum was similar during performance of immediate and delayed responses. However, significant inhibition was observed in the frontal neurons during the delay period. The network activity of visual and frontal cortex displayed smaller number of interneuronal interactions during delayed responses as compared to immediate reactions. The network activity of neurons in the brain structures under study pointed to the interstructural interaction, but only during delayed reactions, steady interneuronal communication was observed between the frontal cortex and dorsal striatum. Thus, both types of estimation of cellular activity revealed differences in the ensemble organization during different types of behavior and showed specific reactions of neuronal ensembles.     

A new visual area on the inferior wall of the cat cruciate sulcus

Properties of 187 neurons in the inferior wall of the cruciate sulcus, in an area where electrical stimulation evoked unidirectional saccadic eye movements, were investigated in waking cats. Of the total number 172 responded to visual stimulation. Neurons in the surface layers of the cortex responded to simple visual stimuli: light or dark spots or bars, both stationary and moving at speeds of around 30 deg/sec. These neurons showed no selectivity as regards stimulus orientation but sometimes behaved selectively toward the direction of their movements. In the intermediate layers the maximal neuronal response was obtained to a model of a bird flaping its wings. Neuronal responses in the depth of the cortex were characterized by selectivity to movement of stimuli toward or away from the animal in a certain part of the visual field, irrespective of whether a light stimulus was presented against a dark background or a dark stimulus against the light background. Responses to visual stimulation were exhibited only if the animal was in a state of activation, when the EEG showed desynchronization, and they were absent in a state of quite wakefulness. No responses were obtained to auditory or somatic stimulation. Responses to visual stimulation were not found in neurons of the medial wall of the brain beneath the cruciate sulcus, but responses were recorded to eye movements of definite size or orientation. It is postulated that at least two contiguous retinotopically organized zones exist in this part of the brain. Activity of one of them is connected with visual function, that of the other with eye movements.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 766–773, November–December, 1984.     

Dynamic Mapping of the Temperature Fields of the Brain

The thermal fields and biopotentials of the brain were studied in 11 healthy subjects in the states of quiet wakefulness and sleep (stages I–IV). To this end, a new method of dynamic radiomapping was applied in parallel with the traditional method of EEG recording. The method of dynamic radiomapping is based on measuring the brain thermal radiation in the decimeter (40 cm) wave range. It allows the integral brain temperature to be recorded from deep inside and up to 2.5 cm from the surface with the help of 12 antennas applied to the skin. The temperature of the cerebral cortex of the human subject in the state of quiet wakefulness varied stochastically in the range of deviations of ±0.3°C in all areas. Changes in the brain functional state, i.e., the transition from wakefulness to sleep, were accompanied by either an increase in the variation range to ±0.5°C or the appearance of stationary foci of heating (by 0.9–1.3°C) or cooling (by –0.7°C) of individual locations and amplitudes.     

Morphophysiologic study of reticulo-cortical pathways in the rabbit

The character of functional connections between the midbrain reticular formation (RF) and the neocortex was studied in rabbits. Unit activity was recorded in sensorimotor cortex by extracellular microelectrode during RF stimulation. Short-latency neuronal reactions were found presumably identified as monosynaptic responses. Results of the studies of anterograde degeneration of myelinic fibers and axonal terminals after electrocoagulation of the RF carried out with the help of electronic microscope allowed to suppose that there were few (less than 0.5 per cent) monosynaptic connections between the RF and the sensorimotor cortex. The main forms of direct connections between these structures were axo-dendritic (situated at the dendritic trunk) and axosomatic synapses at the neurones of the sensorimotor cortex.     

Hippocampal ripples and memory consolidation

During slow wave sleep and quiet wakefulness, the hippocampus generates high frequency field oscillations (ripples) during which pyramidal neurons replay previous waking activity in a temporally compressed manner. As a result, reactivated firing patterns occur within shorter time windows propitious for synaptic plasticity within the hippocampal network and in downstream neocortical structures. This is consistent with the long-held view that ripples participate in strengthening and reorganizing memory traces, possibly by mediating information transfer to neocortical areas. Recent studies have confirmed that ripples and associated neuronal reactivations play a causal role in memory consolidation during sleep and rest. However, further research will be necessary to better understand the neurophysiological mechanisms of memory consolidation, in particular the selection of reactivated assemblies, and the functional specificity of awake ripples.     

Development of coherent neuronal activity patterns in mammalian cortical networks: Common principles and local hetereogeneity

Many mammals are born in a very immature state and develop their rich repertoire of behavioral and cognitive functions postnatally. This development goes in parallel with changes in the anatomical and functional organization of cortical structures which are involved in most complex activities. The emerging spatiotemporal activity patterns in multi-neuronal cortical networks may indeed form a direct neuronal correlate of systemic functions like perception, sensorimotor integration, decision making or memory formation. During recent years, several studies – mostly in rodents – have shed light on the ontogenesis of such highly organized patterns of network activity. While each local network has its own peculiar properties, some general rules can be derived. We therefore review and compare data from the developing hippocampus, neocortex and – as an intermediate region – entorhinal cortex. All cortices seem to follow a characteristic sequence starting with uncorrelated activity in uncoupled single neurons where transient activity seems to have mostly trophic effects. In rodents, before and shortly after birth, cortical networks develop weakly coordinated multineuronal discharges which have been termed synchronous plateau assemblies (SPAs). While these patterns rely mostly on electrical coupling by gap junctions, the subsequent increase in number and maturation of chemical synapses leads to the generation of large-scale coherent discharges. These patterns have been termed giant depolarizing potentials (GDPs) for predominantly GABA-induced events or early network oscillations (ENOs) for mostly glutamatergic bursts, respectively. During the third to fourth postnatal week, cortical areas reach their final activity patterns with distinct network oscillations and highly specific neuronal discharge sequences which support adult behavior. While some of the mechanisms underlying maturation of network activity have been elucidated much work remains to be done in order to fully understand the rules governing transition from immature to mature patterns of network activity.     

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.