Neuronal activity in the amygdaloid structure during the sleep-wake cycle of the rat

The pattern of neuronal spike activity in the amygdaloid structure was studied in the sleep-wake cycle during experiments on unrestrained rats. It was shown that most neurons of the dorsomedial portion of the amygdala display greater spike activity during active wakefulness (80%) and paradoxical sleep (66.7%) than during slow-wave sleep. Most neurons of the basolateral amygdaloid region discharged at high frequency during active wakefulness (84.6%) and during paradoxial sleep (38.4%) compared with the frequency of firing during slow-wave sleep. Some neurons were found whose rate of discharge rose during slow-wave sleep in comparison with a similar period of paradoxical sleep (38.4%) and of active wakefulness (7.7%). Our findings show how the pattern of neuronal activity in the dosromedial and basolateral regions of the amygdaloid structure differs at various stages of the sleep-wake cycle. It is postulated that this structure serves mainly to regulate emotionally motivated processes rather than helping to govern the basic mechanisms of the sleep-wake cycle.Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 747–756, November–December, 1985.     

Single unit activity in the guinea-pig cochlear nucleus during sleep and wakefulness.

The effects of waking and sleep on the response properties of auditory units in the ventral cochlear nucleus (CN) were explored by using extracellular recordings in chronic guinea-pigs. Significant increases and decreases in firing rate were detected in two neuronal groups, a) the "sound-responding" and b) the "spontaneous" (units that do not show responses to any acoustic stimuli controlled by the experimenter). The "spontaneous" may be considered as belonging to the auditory system because the corresponding units showed a suppression of their discharge when the receptor was destroyed. The auditory CN units were characterized by their PSTH in response to tones at their characteristic frequency and also by the changes in firing rate and probability of discharge evaluated during periods of waking, slow wave and paradoxical sleep. The CNS performs functions dependent on sensory inputs during wakefulness and sleep phases. By studying the auditory input at the level of the ventral CN with constant sound stimuli, it was shown that, in addition to the firing rate shifts, some units presented changes in the temporal probability of discharge, implying central actions on the corresponding neurons. The mean latency of the responses, however, did not show significant changes throughout the sleep-waking cycle. The auditory efferent pathways are postulated to modulate the auditory input at CN level during different animal states. The probability of firing and the changes in the temporal pattern, as shown by the PSTH, are thus dependent on both the auditory input and the functional brain state related to the sleep-waking cycle.     

Transitions from Wakefulness to Sleep at Different Times of Day: Old vs. Young Subjects

In order to assess age effects upon the daytime level of alertness, both subjective and objective measures of alertness were obtained in 19 healthy elderly males (mean age 65 years) and 19 healthy young males (mean age 21 years). Subjects were recorded during a Multiple Sleep Latency Test (MSLT), administered at 5 different times of day (9 a.m., 12 a.m., 3 p.m., 6 p.m., 9 p.m.). Before each test, subjects filled out an alertness questionnaire. During the entire 20 minutes of each test electroencephalographic (EEG) recordings were made and transformed into 40 averaged spectra, one for each 30 s epoch. For the delta, theta, alpha, sigma and beta bands of the EEG 6 consecutive values were averaged to obtain 1 value per 3 minutes. On the basis of the visually guided detection of the first spindle, sleep onset was determined. The elderly subjects obtained a higher overall level of subjective alertness than the young subjects. No age effect was observed for sleep latency, which followed a U-shaped diurnal trend. Overall, the mean relative EEG energy values followed a diurnal trend that was the reverse of that for sleep latency. The mean relative delta EEG energy gradually increased, and the mean relative alpha EEG energy gradually decreased across the MSLT. For the young subjects the respective ranges of variation of these EEG bands were very similar, while for the elderly subjects the range of variation of the alpha values was less than half of that for the delta band. Apparently, alpha EEG activity during the wake-sleep transition does not simply covary with delta EEG activity. Moreover, age appears to have a significant effect upon the dynamics of alpha EEG activity during the wake-sleep transition.     

Dynamics of neuronal activity in the cingulate gyrus during the sleep-wake cycle

Dynamics of neuronal activity in the cingulate gyrus (CG) was investigated during the sleep-wake cycle (SWC) of free-ranging cats. The highest activity rate was found to occur in 65.4% of neurons during active emotional consciousness (EC) and the so-called emotional phase of paradoxical sleep (PS), while firing rate decreased during passive consciousness (PC) and slow-wave sleep (SS). Peak firing rate was observed during SS in 15% of neurons, while divisions of activity between stages of the SWC remained the same in 19.6%. In addition, discharge patterns in 75.2% of neurons changed consistently in step with phase shifts. More particularly, neurons fired during EC and PS with single action potentials with a more or less even time distribution, whereas a burst-phase activity pattern occurred in the course of SS. Firing rate declined (in 42.6% of units) or remained unchanged (in 50.4%) in the majority of CG neurons (even amongst those manifesting highest activity during EC and PS) as episodes of isolated EEG arousal developed (whether in the context of SS or as PS wore off). This would indicate that the CG actually contributes to shaping the behavioral state of consciousness. The CG, therefore, as one of the higher divisions of the limbic system, must play a major part in controlling the basic mechanisms of the SWC, as well as emotionally motivated processes evolving in the cycle.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 832–840, November–December, 1989.     

Motor unit activity during long-lasting intermittent muscle contractions in humans

Changes accompanying long-lasting intermittent muscle contractions (30%–50% of the maximal) were investigated by tracing the activity of 38 motor units (MU) of the human biceps brachii muscle recorded from fine-wire branched electrodes. The motor task was a continuous repetition of ramp-and-hold cycles of isometric flexion contractions. During ramp-up phases a significant decline in recruitment thresholds was found with no changes in the discharge pattern. During ramp-down phases the unchanged mean value of derecruitment thresholds during the task was accompanied by increased duration of the last two interspike intervals (ISI). These findings would suggest that during fatigue development the main compensatory mechanism during ramp-up contractions is space coding while for ramp-down contractions it is rate coding. During the steady-state phases the mean value of ISI, as well as the firing variability, had increased by the end of the task in most of the MU investigated . In addition 17 recruited MU were also investigated. These units revealed a lower initial discharge rate and a faster decrease in the mean discharge rate with the development of fatigue. The gradual reduction of the recruitment threshold of already active MU and the recruitment of new units demonstrated an increased excitability of the motorneuron pool during fatigue. A typical recruitment pattern (a first short ISI followed by a long one) was observed during ramp-up contractions in units active from the very beginning of the task, as well as during sustained contractions at the onset of the stable discharge of the additionally recruited MU. Accepted: 23 September 1997     

The role of the medial preoptic area in the organization of paradoxical sleep

Influence of electrical stimulation of the medial preoptic area of cats on characteristics of paradoxical sleep and activity of medial preoptic neurons were studied in the course of sleep-waking cycle. Low-frequency stimulation of this structure in the state of slow-wave sleep evoked short-latency electrocortical desynchronization and induced transition to paradoxical sleep or paradocical sleep-like state. The same stimulation during the whole period of paradoxical sleep results in a reduction of its duration, practically complete disappearance of tonic stage, and increase in the density of rapid eye movements in phasic stage. The vast majority of meurons in the medial preoptic area decreased their firing rates during quiet waking and slow-wave sleep and dramatically increased their activity during paradoxical sleep. More than 50% of such neurons displayed activation 20-70 s prior to the appearance of electrocorticographic correlates of paradoxical sleep. Some neurons were selectively active during paradoxical sleep. Approximately 50% of cells increased their firing rates a few seconds prior to and/or during series of rapid eye movements. The results suggest that the medial preoptic area contains the units of the executive system (network) of paradoxical sleep and are involved in the mechanisms of neocortical desynchronization.     

Spectral-correlation characteristics of the electrical activity of the brain of the rabbit in a state of calm wakefulness

Inter- and intrahemispheric relations of electrical activity of the pre-motor, sensorimotor (representation of forelimb and blinking) and visual zones of rabbit's cerebral cortex in calm alertness was studied by method of spectral-correlative analysis. Mean coherence levels of the EEG of tested hemispheric symmetric points and symmetric pairs of leads in the left and right hemispheres were characterized by a high temporal stability in the state of calm alertness and during sensory stimulation. A comparison of mean coherence values of EEG in symmetric leads, revealed a tendency to left-side dominance of statistical bonds of electrical processes. A tendency was shown towards interhemispheric asymmetry by mean parameters of EEG power spectra: the left hemisphere of the rabbit is characterized by a lower mean frequency of electrical activity and a more narrow effective frequency of the spectrum.     

Temporal patterns of unit activity of mesencephalic reticular nuclei during sleep and waking

Temporal patterns of unit activity in the mesencephalic reticular nuclei (n. cuneiformis, n. parabrachialis) were studied in unrestrained rats during the sleep-waking cycle; activity was derived by means of movable metallic microelectrodes. Analysis of the data showed that most neurons of these mesencephalic reticular nuclei (76 and 66% respectively) generate activity with the highest frequency during active waking and the emotional stage of paradoxical sleep; they discharge with lower frequency during passive wakefulness and the nonemotional stage of paradoxical sleep, and they exhibit least activity during slow-wave sleep. Comparatively few neurons (24 and 15%) demonstrate the opposite kind of temporal pattern of activity: They discharge more intensively during slow-wave sleep and more slowly during active wakefulness and the emotional stage of paradoxical sleep. Activity of these neurons during quiet wakefulness and the nonemotional stage of paradoxical sleep reaches the level of activity observed during slow-wave sleep. Neurons discharging intensively during active wakefulness were found in n. parabrachialis; their discharge frequency during passive wakefulness and slow-wave sleep and its frequency was least during paradoxical sleep. The similarity and differences of the neurophysiological mechanisms of regulation of the phases and stages of the sleepwaking cycle are discussed.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 16, No. 5, pp. 678–690, September–October, 1984.     

Unit activity in the cat visual cortex in the sleep-waking cycle

Changes in spontaneous unit activity in the primary visual cortex during the sleep-waking cycle were studied in chronic experiments on dark-adapted cats. In the cell population studied activity in states of wakefulness and of paradoxical sleep did not differ significantly either in mean discharge frequency or in pattern. Activity of most cells in a state of slow sleep differed significantly from that in states of wakefulness and paradoxical sleep by the development of a "burst-pause" pattern in the unit discharges.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 343–349, July–August, 1976.     

Electroencephalogram bands modulated by vigilance states in an anuran species: a factor analytic approach

Dramatic changes in neocortical electroencephalogram (EEG) rhythms are associated with the sleep–waking cycle in mammals. Although amphibians are thought to lack a neocortical homologue, changes in rest–activity states occur in these species. In the present study, EEG signals were recorded from the surface of the cerebral hemispheres and midbrain on both sides of the brain in an anuran species, Babina daunchina, using electrodes contacting the meninges in order to measure changes in mean EEG power across behavioral states. Functionally relevant frequency bands were identified using factor analysis. The results indicate that: (1) EEG power was concentrated in four frequency bands during the awake or active state and in three frequency bands during rest; (2) EEG bands in frogs differed substantially from humans, especially in the fast frequency band; (3) bursts similar to mammalian sleep spindles, which occur in non-rapid eye movement mammalian sleep, were observed when frogs were at rest suggesting sleep spindle-like EEG activity appeared prior to the evolution of mammals.     

Behavioral and electrophysiological patterns of wakefulness-sleep states in a lizard.

Four individuals of the lizard Ctenosaura pectinata were chronically implanted for electroencephalographic (EEG), electromyographic (EMG) and electro-oculographic (EOG) recordings. Four different vigilance states were observed throughout the nyctohemeral cycle. These states were: Active wakefulness (Aw), quiet wakefulness (Qw), quiet sleep (Qs) and active sleep (As). Each state displayed its own behavioral and electrophysiological characteristics. EEG waves were similar during Aw and Qw but they diminished in amplitude and frequency when passing from these states to Qs, and both parameters increased during As. Muscular activity was intense in Aw, it decreased during Qw and almost disappeared during Qs. This activity reappeared in a phasic way during As, coinciding with generalized motor manifestations. Ocular activity was intense during Aw but minimal during Qw, it disappeared in Qs and was present intermittently in As. Aw, Qw, Qs and As occupied 5.9%, 25.7%, 67.7% and 0.6% of the 24 hr period, respectively. The frequency and duration of As episodes showed great inter-animal variability and the mean duration was of 12.9 sec. Stimuli reaction threshold was highest during sleep. In conclusion, the lizard Ctenosaura pectinata exhibit two sleep phases (Qs and As) that may be assimilated to slow wave sleep (SWS) and paradoxical sleep (PS) of birds and mammals.     

Development of the nocturnal sleep electroencephalogram in human infants

The development of nocturnal sleep and the sleep electroencephalogram (EEG) was investigated in a longitudinal study during infancy. All-night polysomnographic recordings were obtained at home at 2 wk and at 2, 4, 6, and 9 mo after birth (analysis of 7 infants). Total sleep time and the percentage of quiet sleep or non-rapid eye movement sleep (QS/NREMS) increased with age, whereas the percentage of active sleep or rapid eye movement sleep (AS/REMS) decreased. Spectral power of the sleep EEG was higher in QS/NREMS than in AS/REMS over a large part of the 0.75- to 25-Hz frequency range. In both QS/NREMS and AS/REMS, EEG power increased with age in the frequency range <10 Hz and >17 Hz. The largest rise occurred between 2 and 6 mo. A salient feature of the QS/NREMS spectrum was the emergence of a peak in the sigma band (12-14 Hz) at 2 mo that corresponded to the appearance of sleep spindles. Between 2 and 9 mo, low-frequency delta activity (0.75-1.75 Hz) showed an alternating pattern with a high level occurring in every other QS/NREMS episode. At 6 mo, sigma activity showed a similar pattern. In contrast, theta activity (6.5-9 Hz) exhibited a monotonic decline over consecutive QS/NREMS episodes, a trend that at 9 mo could be closely approximated by an exponential function. The results suggest that 1) EEG markers of sleep homeostasis appear in the first postnatal months, and 2) sleep homeostasis goes through a period of maturation. Theta activity and not delta activity seems to reflect the dissipation of sleep propensity during infancy.     

Comparison of spontaneous activity of mesencephalic reticular neurones in the waking state and during pentobarbital anaesthesia.

In rats immobilized by d-Tubocurarine the spontaneous activity of 100 mesencephalic reticular neurones was recorded extracellularly and statistically evaluated before and after repeated intravenous administration of 15 mg/kg doses of Pentobarbital. Number of spontaneously active neurones decreases quasi-linearly with repeated 15 mg/kg Pentobarbital doses. After a 75 mg/kg cumulative dose practically all neurones ceased firing spontaneously, whereas cortical EEG activity fully disappeared after the 90 mg/kg Pentobarbital dose. The firing rate was characterized by the mean interval with its standard deviation. Mean value for the total sample of spontaneously active neurones was 146.7 +/- 192.3 msec without Pentobarbital and increased to 302.7 +/- 367.5 msec after 15 mg/kg and to 400.6 +/- 452.5 msec after 30 mg/kg cumulative dose of Pentobarbital. The 15 mg/kg dose increased the frequency of firing in 5% of neurones only. The most often encountered type of interval histogram in the mesencephalic reticular formation was the exponential type (59% in unanaesthetized state), which was also most sensitive to Pentobarbital. Synchronized activity in bursts, characterized by periodical peaks and dips frequently occurred in neurones with the exponential-like interspike interval density after Pentobarbital administration. On the contrary, neurones with gamma-like and especially with symmetrical-like types of density were less influenced by Pentobarbital. In many neurones a periodical increase in the firing rate (with intervals of tens of seconds) related to the occurrence of spindles was present in the cortical EEG activity.     

Simultaneous single unit recording in the mitral cell layer of the rat olfactory bulb under nasal and tracheal breathing

Odor perception depends on the odorant-evoked changes on Mitral/Tufted cell firing pattern within the olfactory bulb (OB). The OB exhibits a significant "ongoing" or spontaneous activity in the absence of sensory stimulation. We characterized this ongoing activity by simultaneously recording several single neurons in the mitral cell layer (MCL) of anesthetized rats and determined the extent of synchrony and oscillations under nasal and tracheal breathing. We recorded 115 neurons and found no significant differences in the mean firing rates between both breathing conditions. Surprisingly, nearly all single units exhibited a long refractory period averaging 14.4 ms during nasal respiration that was not different under tracheal breathing. We found a small incidence (2% of neurons) of gamma band oscillations and a low incidence (8.1%) of correlated firing between adjacent MCL cells. During nasal respiration, a significant oscillation at the respiratory rate was observed in 12% of cells that disappeared during tracheal breathing. Thus, in the absence of odorants, MCL cells exhibit a long refractory period, probably reflecting the intrinsic OB network properties. Furthermore, in the absence of sensory stimulation, MCL cell discharge does not oscillate in the gamma band and the respiratory cycle can modulate the firing of these cells.     

State-related discharge of neurons in the brainstem of freely moving box turtles, Terrapene carolina major

We have performed the first study of neuronal activity in freely-moving reptiles. 23 brainstem units were recorded from areas throughout the reticular formation, during wakefulness and quiescence in the box turtle. These units responded to various sensory stimuli and increased firing rates in relation to motor activity during wakefulness. All but one unit showed significant decreases in discharge during quiescence. Group I cells (32%) fired mostly during active movements and exhibited silent periods of 5 min or longer during quiescence while group II cells (68%) maintained slow tonic activity in quiescence. Polygraphic data showed no consistent, cyclically occurring phasic events during quiescence.     

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.     

Regional slow waves and spindles in human sleep

The most prominent EEG events in sleep are slow waves, reflecting a slow (<1 Hz) oscillation between up and down states in cortical neurons. It is unknown whether slow oscillations are synchronous across the majority or the minority of brain regions--are they a global or local phenomenon? To examine this, we recorded simultaneously scalp EEG, intracerebral EEG, and unit firing in multiple brain regions of neurosurgical patients. We find that most sleep slow waves and the underlying active and inactive neuronal states occur locally. Thus, especially in late sleep, some regions can be active while others are silent. We also find that slow waves can propagate, usually from medial prefrontal cortex to the medial temporal lobe and hippocampus. Sleep spindles, the other hallmark of NREM sleep EEG, are likewise predominantly local. Thus, intracerebral communication during sleep is constrained because slow and spindle oscillations often occur out-of-phase in different brain regions.     

Discharge patterns of cochlear ganglion neurons in the chicken

Summary Physiological recordings were made of the compound action potential from the round window and single neurons in the cochlear ganglion of normal adult chickens (Gallus domesticus). The compound action potential threshold to tone bursts decreased from approximately 42 dB at 0.25 kHz to 30 dB between 1 and 2 kHz and then increased to 51 dB at 4 kHz. Most of the cochlear ganglion cells had characteristic frequencies below 2 kHz and the thresholds of most neurons were roughly 30–35 dB lower than the compound action potential thresholds. At any given characteristic frequency, thresholds varied by as much as 60 dB and units with the highest thresholds tended to have the lowest spontaneous rates. Spontaneous discharge rates ranged from 0 to 200 spikes/s with a mean rate of 86 spikes/s. Interspike interval histograms of spontaneous activity often contained regular peaks with the time interval between peaks approximately equal to 1/(characteristic frequency). Tuning curves were sharply tuned and V-shaped with approximately equal slopes to the curves above and below characteristic frequency. Q_10dB and Q_30dB values for the tuning curves increased with characteristic frequency. Post stimulus time histograms showed sustained firing during the stimulus and were characterized by a slight-to-moderate peak at stimulus onset. Most units showed vigorous phase-locking to tones at characteristic frequency although the degree of phase-locking declined sharply with increasing characteristic frequency. Discharge rate-level functions at characteristic frequency had a mean dynamic range of 42 dB and a mean saturation firing rate of 327 spikes/s. In general, the firing patterns of cochlear ganglion neurons are similar in most respects to those reported in other avians, but differ in several important respects from those seen in mammals.Abbreviations CF characteristic frequency - CAP compound action potential     

Cataplexy-active neurons in the hypothalamus: implications for the role of histamine in sleep and waking behavior

Noradrenergic, serotonergic, and histaminergic neurons are continuously active during waking, reduce discharge during NREM sleep, and cease discharge during REM sleep. Cataplexy, a symptom associated with narcolepsy, is a waking state in which muscle tone is lost, as it is in REM sleep, while environmental awareness continues, as in alert waking. In prior work, we reported that, during cataplexy, noradrenergic neurons cease discharge, and serotonergic neurons greatly reduce activity. We now report that, in contrast to these other monoaminergic "REM-off" cell groups, histamine neurons are active in cataplexy at a level similar to or greater than that in quiet waking. We hypothesize that the activity of histamine cells is linked to the maintenance of waking, in contrast to activity in noradrenergic and serotonergic neurons, which is more tightly coupled to the maintenance of muscle tone in waking and its loss in REM sleep and cataplexy.     

Inspiratory neuron activity in the ventrolateral medulla of the dog

The purpose of this study was to describe the distribution and activity pattern of respiratory neurons located in the ventrolateral medulla (VLM) of the dog. Spike activity of 129 respiratory neurons was recorded in 23 ketamine-anesthetized spontaneously breathing dogs. Pontamine blue dye was used to mark the location of each neuron. Most VLM neurons displaying respiratory related spike patterns were located in a column related closely to ambigual and retroambigual nuclei. Both inspiratory and expiratory neurons were present with inspiratory units being grouped more rostrally. The predominant inspiratory neuron firing pattern was "late" inspiratory, although eight "early" types were located. All expiratory firing patterns were the late expiratory variety. Each neuron burst pattern was characterized by determining burst duration (BD), spikes per burst (S/B), peak frequency (PF), time to peak frequency (TPF), rate of rise to peak frequency (PF/TPF), and mean frequency. CO2-induced minute ventilation increases were associated with decreases in BD and TPF and increases in PF, S/B, and PF/TPF. In 11 experiments the relative influences of vagotomy and tracheal occlusion on late inspiratory units were compared. Tracheal occlusion increased late inspiratory BD and S/B but did not alter PF/TPF. Vagotomy increased BD and S/B beyond those obtained by tracheal occlusion and, in some neurons, decreased the PF/TPF. We conclude that the location of respiratory units in the VLM of the dog is similar to that in other species, the discharge pattern of VLM respiratory units is similar to those in cat VLM, and vagotomy and tracheal occlusion affect discharge patterns differently.