[The history of observations and some methodological features of the studies on local sleep]. / K istorii nablyudeniya i nekotorym metodicheskim osobennostyam issledovaniya proyavlenii lokal'nogo sna.

The phenomenon of local sleep, a concept that has come into somnology relatively recently, has been attracting more and more attention of researchers. Under this name, two groups of phenomena are considered. The first is the appearance in different parts of the cerebral cortex of different EEG patterns during general sleep. The second is the disconnection of certain cortical areas from the processing of extero- or proprioceptive signals and their transition to spiking and slow wave electrical activity, which is typical for sleep, while awake. The authors believe that it is the second phenomenon that can be called real local sleep. The appearance of local cortical sleep is inseparably linked with the occurrence of local wakefulness. It can be expected that the occurrence of local sleep will have detrimental consequences for behavior in urgent and complicated situations, while local wakefulness can adversely affect the visceral health of the body. A possible way of early detection of the local sleep development is proposed. In conclusion, some methodological problems on the way of electrophysiological studies of the local aspects of sleep and wakefulness are considered.

[On the mechanism of therapeutic effects of electrostimulation. Interpretations and predictions based on the results of sleep studies]. / K mekhanizmu terapevticheskogo éffekta élektrostimuliatsii. Interpretatsii i predskazaniia, osnovannye na rezul'tatakh issledovanii sna.

Based on the studies of the transition from wakefulness to sleep, we propose that therapeutic effect of various types of electrical stimulations can be related to growing sleepiness promoted by the stimulation, and to the improvement of sleep quality resulted from this procedure. Namely, improved sleep but not the stimulation itself will cause the therapeutic effect. The authors also discuss the probable mechanisms of the anticonvulsive effects of the vagus nerve stimulation and suggest that this effect could be caused by the changes in rhythmical activity of the visceral organs as a result of stimulation. Changes in these frequencies will shift them out of the resonance range of the cortical neuronal circuits, towards which propagation of these visceral signals is opened during sleep.

[Progress of sleep studies in the age of electrophysiology. The visceral theory of sleep]. / Progress izucheniia sna v épokhu élektrofiziologii. Vistseral'naia teoriia sna.

Electrophysiological methods of studying the nervous system have opened up new opportunities for investigations of sleep. Striking changes in the pattern of EEG during the transition from wakefulness to sleep made it's recording a mandatory element of any somnological research. It was also found that the frequency of neuronal firing in the cerebral cortex during sleep does not decrease, but can significantly exceed the average level of the cortical activity during wakefulness. But it remained the main mystery of sleep, what was associated with this high activity of cortical neurons at a time when the thresholds of sensory perception raised and the propagation of signals from the outside world and from the own body towards the cerebral cortex were almost blocked. The resolution of this paradoxical situation was suggested by the visceral theory of sleep. This theory was based on the assumption that during sleep interoceptive afferentation from all visceral systems of the body arrives for analysis into the cerebral cortex. This article offers an overview of the studies performed for direct experimental verification of non-trivial predictions of this theory.

[Long and difficult way towards the understanding of sleep function. Period before the age of electrophysiology]. / Dolgii i trudnyi put' k ponimaniiu naznacheniia sna. Étap do épokhi poiavleniia élektrofiziologii.

It was proposed that historical analysis of ideas concerning the function of sleep will help to evaluate the tendencies in this field of science and will show the probable direction for further approach to understanding of this problem. We reviewed ideas of Ivan Pavlov and his Russian forerunners (Ivan Tarkhanoff and Maria Manaceine) and followers (Nikolay Rozjanskiy and Konstantin Bykov) on the functional role of sleep. This analysis led to the conclusion that state of sleep have been connected with realization of such functional operations, which have not been considered in the past and are not under consideration in the present neuroscience. Thus, one can expect that real understanding of sleep function will come only with new neurophysiologic paradigm.

[Changes in the intragastric contents during sleep affect the statistical characteristics of the neuronal activity in cerebral cortex].

Firing activity in somatosensory cortical area was analyzed in cats during slow wave sleep. Statistical characteristics of the background activity were calculated before and after changes of the intragastric contents (introduction of 50 ml of water into stomach). This procedure did not affect the depth of sleep. There were no changes of the mean firing frequency and the local variation coefficients. To evaluate the degree of chaos in neuronal firing before and after changes of the intragastric contents, the dependence of the Fano factor from the length of the intervals of analysis was calculated. This dependence before water infusion for 40 neurons expressed as a power function with index of power > 0.2 what indicated on fractal nature of the background activity. The changes of the gastric contents in 18 neurons lead to considerable changes of the indexes of power of this function. It is known that in wakefulness for cortical neurons these indexes are dependent on the specific sensory stimulation. Thus, our results can be considered as an indication that during slow wave sleep signals from stomach are included in the afferent flow to the cortical areas, which in wakefulness are involved in somatosensory functions.

[General statistical characteristics of the background firing in cat's cortical neurons during slow-wave sleep].

Background activity of 62 neurons in cat cerebral cortex was recorded in the state of slow-wave sleep for evaluation of the firing statistics. In according to their statistical characteristics neurons were subdivided in three groups. In the first group deviation from the Poisson process were comparatively small, and revealed as fragments of increased excitability following immediately after the refractory period. Second group demonstrated positive correlation of the neighbouring interspike intervals what was conditioned by the changes of the mean firing rate. In these neurons the number of spikes included into the bursts reduced after random permutation of the interspike intervals. The third group was characterized by the big number of spikes included into the bursts (> 15%), and number of bursts usually dropped down after random permutation. Some neurons of this group had constant interspike intervals within the bursts while in other units these intervals monotonically increased toward the end of the burst. Only limited number of neurons demonstrated maximums of the autocorrelation function corresponded to the frequency of the EEG delta activity.

[The visceral theory of sleep].

The review focuses on the studies which were undertaken in order to check our visceral hypothesis of sleep. The review presents also independent studies, results of which are in good agreement with this hypothesis. The visceral hypothesis proposes that during sleep central nervous system including all cortical areas switches from the processing of the exteroceptive information (visual, somatosensory and so on) to the processing of the interoceptive information coming from all visceral systems of an organism. This change of the cortical afferentation during sleep proposes simultaneous change of the directions of the efferent cortical information flows. In wakefulness these flows were directed towards the structures involved in organization of behavior. During sleep they will be redirected towards the structures undertaking visceral regulation. Analysis of the visceral hypothesis of sleep shows that many disorders connected with sleep-wake cycle can be explained by asynchronous switches of the cortical afferent and efferent information flows.

Cortical visual areas process intestinal information during slow-wave sleep.

BACKGROUND: Previously we have shown that, during sleep, electrical and magnetic stimulation of areas of the stomach and small intestine evoked neuronal and EEG responses in various cortical areas. In this study we wanted to correlate natural myoelectrical activity of the duodenum with cortical neuronal activity, and to investigate whether there is a causal link between them during periods of slow-wave sleep. METHODS: We have recorded the myoelectrical activity from the wall of the duodenum and activity of single neurons from three cortical visual areas in naturally sleeping cats and investigated causal interrelationship between these structures during slow-wave sleep. KEY RESULTS: About 30% of the cortical neurons studied changed their firing rate dependent on the phases of the peristaltic cycle and demonstrated selectivity to particular pattern of duodenal myoelectrical activity during slow-wave sleep. This interrelationship was never seen when awake. CONCLUSIONS & INFERENCES: This observation supports the hypothesis that, during sleep, the cerebral cortex switches from processing of exteroceptive and proprioceptive information to processing of interoceptive information.

[Sleep, emotions and the visceral control].

It is known that sleep is connected with sensory isolation of the brain, inactivation of the consciousness and reorganization of the electrical activity in all cerebral cortical areas. On the other hand, sleep deprivation leads to pathology in visceral organs and finally to the death of animals, while there are no obvious changes in the brain itself. It stays the opened question how the changes in the brain activity during sleep could be con- nected with the visceral health? We proposed that the same brain areas and the same neurons, which in wakefulness process the information coming from the distant and proprioreceptors, switch during sleep to the processing of the interoceptive information. Thus, central nervous system is involved into the regulation of the life support functions of the body during sleep. Results of our experiments supported this hypothesis, explained many observations obtained in somnology and offered the mechanisms of several pathological states connected with sleep. However, at the present level of the visceral sleep theory there were no understanding of the well known link between the emotional states of the organisms and transition from wakefulness to sleep, and sleep quality. In this study the attempt is undertaken to combine the visceral theory of sleep with the need- informational theory ofemotions, proposed by P. Simonov. The visceral theory of sleep proposes that in living organisms there is a constant monitoring of the correspondence of the visceral parameters to the genetically determined values. Mismatch signals evoke the feeling of tiredness and the need of sleep. This sleep need en- ters the competition with the other actual needs of the organism. In according with the theory of P. Simonov emotions connected with a particular need play important role in their ranking for satisfaction. We propose that emotional estimation of the sleep need, based on the visceral signals, is realized in the same brain structures which undertake this estimation for other behavioral needs in wakefulness. During sleep, the same brain structures, involved in estimation of emotions, continue to rank the visceral needs and to define their order for processing in the cortical areas and in the highest level of the visceral integration. In the context of the proposed hypothesis, we discuss the results of the studies devoted to investigation of the link between sleep and emotions.

Distance modulated neuronal activity in the cortical visual areas of cats.

During previous studies in cats and monkeys, it was found that in some neurons, responses to visual stimuli of the same angular size were dependent on the absolute distance to these stimuli. To study how widely this peculiarity of visual responses is distributed among cortical visual areas, we recorded activity of neurons in areas V4A, V2, V1, and frontal visual area on the lower bank of the cruciate sulcus. Neuronal activity was recorded at near (20 cm) or far (3 m) distances from a 3D stationary visual scene. Visual scenes were vertically corrugated light gray screens. Angular dimensions of the screens were the same at short and far distances. Eye movements were free during the test procedure. It was found that about 20% of neurons in areas V4A, V1, and frontal visual area had significantly different levels of activity, while animals were looking at the visual scenes located near or far from the eyes. No neurons with depth modulated activity were found in area V2.

[The sleep and the visceral function control].

The review focuses on rapidly growing body of data indicating that disturbances of the natural sleep and sleep deprivation lead to various visceral disorders. The review mentions consequences of sleep disturbances on the gastro-intestinal system, cardio-vascular and respiratory, immune, endocrine and reproductive functions. In order to establish the functional link between the sleep and the visceral health it is proposed that during sleep the central nervous system including all cortical areas switches from the processing of the exteroceptive information to the processing of the interoceptive information. Review of the studies, which offer the direct confirmation of this hypothesis, is presented.

Visually triggered K-complexes: a study in New Zealand rabbits.

K-complexes are the EEG elements recorded during the state of developing sleep and during slow wave sleep. They are the only EEG components which can be elicited by sensory stimulation during sleep. The peculiarity of New Zealand rabbits to sleep with their eyes open allows the use of visual stimuli to elicit K-complexes. Experiments were performed with three rabbits. For visual stimulation, an elongated screen illuminated by LED flashes was attached to an implant on the animal's skull. The screen covered 20-120° of the visual field of one eye, and moved with the head during animal motion. One-millisecond flashes (15-s interval) were used during daytime in an illuminated room. Flashes elicited evoked responses, which, during the first stages of sleep, were often accompanied by K-complexes. The induced K-complexes were recorded from electrodes located both above visual and somatosensory areas. Evoked responses to visual stimuli were also recorded from both pairs of electrodes, although they were generated exclusively in the visual cortex. Correlation analysis showed that visual evoked responses and K-complexes induced by this stimulation were generated in visual cortex, and passively spread to the electrodes above the somatosensory area. Investigation of the latencies of induced K-complexes revealed two time windows when these complexes could be seen. Within each window there was no correlation between latency and amplitude of K-complexes. There was also no correlation between amplitudes of the visual evoked responses and K-complexes elicited by these responses. We propose that visual stimulation in light sleep temporarily opens a gate for some independent external signals, which evoke activation of the visual cortex, reflected in K-complexes.

A minimally invasive and reversible system for chronic recordings from multiple brain sites in macaque monkeys.

We have developed a reversible system for performing simultaneous recordings from multiple brain areas of trained macaque monkeys. It consists of a near-circular halo fitted around the head of the monkey with 5-10 thin plastic or stainless steel posts that either jut against or are screwed into the skull, respectively. Both methods of implantation of the posts are easily reversible, enabling protracted recordings over many years and training the monkeys in more complex tasks. The former is more useful for shorter periods of recordings (2-4 months) separated by long intervals and the latter for longer periods of recordings at a time (6-12 months). With both systems, essentially the entire scalp is intact, allowing multi-site recordings from a number of dorsal cortical areas, as well as other areas, simultaneously. These recordings are performed through tiny craniotomies of usually less than 2mm diameter, which are fitted with small plastic cones that serve as guide tubes for the microelectrodes. The surgery involved in these procedures is relatively minor compared to classical methods and the implants are also usually free of infections, thus requiring little maintenance of recording chambers.

Whether radial receptive field organization of the fourth extrastriate crescent (area V4A) gives special advantage for analysis of the optic flow. Comparison with the first crescent (area V2).

Recently, elongated comet-shaped receptive fields were discovered in the fourth extrastriate crescent (area V4A) of cats and monkeys. It was shown that the long axes of these receptive fields were oriented radially toward the centre of the retina. Such unusual "radial" organization of this extrastriate area led to the assumption that these neurons may contribute to the analysis of optic flow. To investigate this assumption we recorded activity of neurons in the V4A of cats during real motion in depth toward or away from a stationary visual scene. Responses of neurons in area V4A were compared with activity of neurons in area V2 under similar conditions of stimulation. Area V2 is known to be sensitive to motion but does not have radial organization. It was found that a substantial number of visual neurons in both areas did not fire at all when cats were exposed to motion in depth. Nevertheless, neurons with selective activation to direction of motion in depth were identified, but comparable numbers were found in both areas studied. We conclude that radial organization of the fourth extrastriate crescent does not provide any special advantage for the analysis of optic flow information.

Neurons with large bilateral receptive fields in monkey prelunate gyrus.

In single-cell recordings from the dorsocaudal part of the prelunate gyrus of an alert monkey (Macaca fascicularis) we found neurons with unexpectedly large receptive fields (RFs) that spread bilaterally into the contra- and ipsilateral visual fields. These neurons (n=82) appeared to be clustered in the periphery of V4. They were surrounded by neurons with relatively small (3-10 degrees) and unilateral RFs in the contralateral field with properties similar to those previously described for neurons in area V4. Bilateral RFs extended over large parts of the lower visual field but always spared the fovea. Receptive fields typically revealed two foci of maximal responsiveness that were arranged symmetrically in the ipsi- and contralateral fields. Twenty-six cells did not respond to stimuli along the vertical meridian; these neurons had two distinct RFs. The preference for stimulus orientation, color, or motion was similar in all parts of these large RFs.

Neuronal responses to orientation and motion contrast in cat striate cortex.

Responses of striate neurons to line textures were investigated in anesthetized and paralyzed adult cats. Light bars centered over the excitatory receptive field (RF) were presented with different texture surrounds composed of many similar bars. In two test series, responses of 169 neurons to textures with orientation contrast (surrounding bars orthogonal to the center bar) or motion contrast (surrounding bars moving opposite to the center bar) were compared to the responses to the corresponding uniform texture conditions (all lines parallel, coherent motion) and to the center bar alone. In the majority of neurons center bar responses were suppressed by the texture surrounds. Two main effects were found. Some neurons were generally suppressed by either texture surround. Other neurons were less suppressed by texture displaying orientation or motion (i.e. feature) contrast than by the respective uniform texture, so that their responses to orientation or motion contrast appeared to be relatively enhanced (preference for feature contrast). General suppression was obtained in 33% of neurons tested for orientation and in 19% of neurons tested for motion. Preference for orientation or motion contrast was obtained in 22% and 34% of the neurons, respectively, and was also seen in the mean response of the population. One hundred nineteen neurons were studied in both orientation and motion tests. General suppression was correlated across the orientation and motion dimension, but not preference for feature contrast. We also distinguished modulatory effects from end-zones and flanks using butterfly-configured texture patterns. Both regions contributed to the generally suppressive effects. Preference for orientation or motion contrast was not generated from either end-zones or flanks exclusively. Neurons with preference for feature contrast may form the physiological basis of the perceptual saliency of pop-out elements in line textures. If so, pop-out of motion and pop-out of orientation would be encoded in different pools of neurons at the level of striate cortex.

Two visual areas located in the middle suprasylvian gyrus (cytoarchitectonic field 7) of the cat's cortex.

Neuronal properties and topographic organization of the middle suprasylvian gyrus (cortical cytoarchitectonic field 7) were studied in three behaving cats with painlessly fixed heads. Two main neuronal types were found within this field. Type 1 neurons occupied the lateral part of the field and bordered representation of directionally selective neurons of the lateral suprasylvian visual area by vertical retinal meridian. Type 1 neurons had elongated and radially oriented receptive fields located in the lower part of contralateral visual field. Type 1 neurons preferred stimuli moving out or to the centre of gaze at a low or moderate speed, and many of them were depth selective. The responses were enhanced by attention, oriented to the presented stimulus. Medial part of the field 7 along the border with the area V3 was occupied by neurons with not elongated receptive fields (type 2). These neurons preferred moderate and high speeds of motion, and gratings of proper spatial frequency and orientation were effective stimuli for them. Border between representations of type 2 and type 1 neurons coincided with projection of horizontal retinal meridian. At the rostral and caudal borders of the field 7 abrupt changes of neuronal properties took place. Neurons which abutted field 7 anteriorly and posteriorly resembled hypercomplex cells and their small receptive fields were located in the central part of the visual field. Topographical considerations and receptive field properties allowed us to conclude that the medial part of the field 7 (included type 2 neurons) is functionally equivalent to the area V4 in the cortex of primates, while the lateral part (type 1 neurons) may correspond to the area V4T.

Evidence for asynchronous development of sleep in cortical areas.

We have recorded from extrastriate area V4 in monkeys performing a visual search task. When animals became tired or drowsy, responses to visual stimulation were often reduced or even completely blocked, and background activity changed to the burst-pause pattern typically seen in sleep. In spite of such neuronal sleep observed in V4, animals continued to perform the visual task, indicating that at least the primary visual cortex was still working. This observation shows that sleep does not develop simultaneously in all cortical areas but may affect some areas earlier than others. In particular conditions, local sleep of certain areas may be a stable and long-lasting phenomenon.

Neuronal correlates of pop-out in cat striate cortex.

Neuronal responses to static and moving texture patterns were investigated in the striate cortex of anaesthetized and paralysed adults cats. Texture patterns were composed of a central light bar presented in the excitatory receptive field of a cell and an array of many similar elements in the surround. For the static condition, elements in the surround were either parallel or orthogonal to the centre line (orientation test). For the moving condition, centre and surround elements (all at same orientation) moved either in the same or in the opposite directions (motion test). Thirty-six percent (31/86) of the neurons tested for motion and 24% (24/99) of the neurons tested for orientation responded more strongly to the patterns displaying feature contrast than to the uniform patterns. These neurons may form a neural basis for visual pop-out of orientation and motion.

A reversible system for chronic recordings in macaque monkeys.

We propose a system for head fixation and neuronal recording that minimizes surgery for implantation. Fixation is obtained by posts which are attached to the opposite sides of the skull and are connected by a rigid frame around the animal's head. As forces are counterbalanced and distributed around the head, the system does not need to be implanted into the skull, and thus allows for continuous adjustment to the growing skull in young animals. Except for small incisions for the posts, the skin over the skull is left intact. Recording is achieved through small bone holes which are easily reached by means of conical guide tubes. The system provides perfect stability of recording, allows flexible access to various areas of the brain and can be easily removed during longer pauses in experiments. The use of this system may also decrease the number of laboratory animals needed.