A key role for the caudoventral pontine tegmentum in the simultaneous generation of eye saccades in bursts and associated ponto-geniculo-occipital waves during paradoxical sleep in the cat

The Ponto-Geniculo-Occipital (PGO) Waves in Dreaming: An Overview

Rapid eye movement (REM) sleep is the main sleep correlate of dreaming. Ponto-geniculo-occipital (PGO) waves are a signature of REM sleep. They represent the physiological mechanism of REM sleep that specifically limits the processing of external information. PGO waves look just like a message sent from the pons to the lateral geniculate nucleus of the visual thalamus, the occipital cortex, and other areas of the brain. The dedicated visual pathway of PGO waves can be interpreted by the brain as visual information, leading to the visual hallucinosis of dreams. PGO waves are considered to be both a reflection of REM sleep brain activity and causal to dreams due to their stimulation of the cortex. In this review, we summarize the role of PGO waves in potential neural circuits of two major theories, i.e., (1) dreams are generated by the activation of neural activity in the brainstem; (2) PGO waves signaling to the cortex. In addition, the potential physiological functions during REM sleep dreams, such as memory consolidation, unlearning, and brain development and plasticity and mood regulation, are discussed. It is hoped that our review will support and encourage research into the phenomenon of human PGO waves and their possible functions in dreaming.

A cognitive process occurring during sleep is revealed by rapid eye movements

Since the discovery of rapid eye movement (REM) sleep, the nature of the eye movements that characterize this sleep phase has remained elusive. Do they reveal gaze shifts in the virtual environment of dreams or simply reflect random brainstem activity? We harnessed the head direction (HD) system of the mouse thalamus, a neuronal population whose activity reports, in awake mice, their actual HD as they explore their environment and, in sleeping mice, their virtual HD. We discovered that the direction and amplitude of rapid eye movements during REM sleep reveal the direction and amplitude of the ongoing changes in virtual HD. Thus, rapid eye movements disclose gaze shifts in the virtual world of REM sleep, thereby providing a window into the cognitive processes of the sleeping brain.

Neurons in the Nucleus papilio contribute to the control of eye movements during REM sleep

Rapid eye movements (REM) are characteristic of the eponymous phase of sleep, yet the underlying motor commands remain an enigma. Here, we identified a cluster of Calbindin-D28K-expressing neurons in the Nucleus papilio (NP^Calb), located in the dorsal paragigantocellular nucleus, which are active during REM sleep and project to the three contralateral eye-muscle nuclei. The firing of opto-tagged NP^Calb neurons is augmented prior to the onset of eye movements during REM sleep. Optogenetic activation of NP^Calb neurons triggers eye movements selectively during REM sleep, while their genetic ablation or optogenetic silencing suppresses them. None of these perturbations led to a change in the duration of REM sleep episodes. Our study provides the first evidence for a brainstem premotor command contributing to the control of eye movements selectively during REM sleep in the mammalian brain.

Rapid eye movement (REM) sleep is a sleep phase characterised by random eye movements for which the underlying motor commands are yet to be revealed. The authors describe that a cluster of medulla oblongata neurons in the Nucleus papiliocontributes to the control of eye movements during REM sleep.

Michel Jouvet: an explorer of dreams and a great storyteller

In the late 50s Michel Jouvet discovered the presence of muscle atonia during REM sleep in cats and created the first model of REM sleep behavior disorder. He built and led in Lyon, France, the "Laboratory of Molecular Dream Science" (a merry oxymoron to silently protest against the research policy of favoring molecular biology over physiology), where in the late 80s, you could cross people who had worked on sleep in the python, tench fish, tortoise, iguana, hen, lamb, mouse, rat and cat. This brilliant physiologist was also a great storyteller with a very good sense of humor. He supported the theory that dreaming is equivalent to REM sleep (which he called "paradoxical sleep"), kept his own dream diary, and imagined that the ponto-geniculo-occipital waves during REM sleep could compose the song sheet of dreams. He wrote several books published in French on dreams and dreaming.

Towards a Functional Understanding of PGO Waves

Ponto-Geniculo-Occipital (PGO) waves are biphasic field potentials identified in a range of mammalian species that are ubiquitous with sleep, but can also be identified in waking perception and eye movement. Their role in REM sleep and visual perception more broadly may constitute a promising avenue for further research, however what was once an active field of study has recently fallen into stasis. With the reality that invasive recordings performed on animals cannot be replicated in humans; while animals themselves cannot convey experience to the extent required to elucidate how PGO waves factor into awareness and behavior, innovative solutions are required if significant research outcomes are to ever be realized. Advances in non-invasive imaging technologies and sophistication in imaging methods now offer substantial scope to renew the study of the electrophysiological substrates of waking and dreaming perception. Among these, Magnetoencephalogram (MEG) stands out through its capacity to measure deep brain activations with high temporal resolution. With the current trend in sleep and dream research to produce translational findings of psychopathological and medical significance, in addition to the clear links that PGO wave generation sites share, pharmacologically, with receptors involved in expression of mental illness; there is a strong case to support scientific research into PGO waves and develop a functional understanding of their broader role in human perception.

Central control of cardiovascular function during sleep

There is increasing evidence that cardiovascular control during sleep is relevant for cardiovascular risk. This evidence warrants increased experimental efforts to understand the physiological mechanisms of such control. This review summarizes current knowledge on autonomic features of sleep states [non-rapid-eye-movement sleep (NREMS) and rapid-eye-movement sleep (REMS)] and proposes some testable hypotheses concerning the underlying neural circuits. The physiological reduction of blood pressure (BP) during the night (BP dipping phenomenon) is mainly caused by generalized cardiovascular deactivation and baroreflex resetting during NREMS, which, in turn, are primarily a consequence of central autonomic commands. Central commands during NREMS may involve the hypothalamic ventrolateral preoptic area, central thermoregulatory and central baroreflex pathways, and command neurons in the pons and midbrain. During REMS, opposing changes in vascular resistance in different regional beds have the net effect of increasing BP compared with that of NREMS. In addition, there are transient increases in BP and baroreflex suppression associated with bursts of brain and skeletal muscle activity during REMS. These effects are also primarily a consequence of central autonomic commands, which may involve the midbrain periaqueductal gray, the sublaterodorsal and peduncular pontine nuclei, and the vestibular and raphe obscurus medullary nuclei. A key role in permitting physiological changes in BP during sleep may be played by orexin peptides released by hypothalamic neurons, which target the postulated neural pathways of central autonomic commands during NREMS and REMS. Experimental verification of these hypotheses may help reveal which central neural pathways and mechanisms are most essential for sleep-related changes in cardiovascular function.

Hallucinations in narcolepsy with and without cataplexy: contrasts with Parkinson's disease

BACKGROUND

Narcolepsy and Parkinson's disease (PD) are associated with hallucinations, excessive daytime sleepiness, REM sleep behavior disorder (RBD), as well as complete (narcolepsy with cataplexy) vs. partial (PD, narcolepsy without cataplexy) hypocretin-1 deficiency.

OBJECTIVE

To compare the hallucinations associated with narcolepsy to those of PD.

METHODS

One hundred patients with narcolepsy (with and without cataplexy) and 100 patients with PD were consecutively interviewed about their hallucinations (frequency, phenomenology, insight into unreality and association with sleep) as well as their risk factors.

RESULTS

Hallucinations occurred more frequently and with more motor and multimodal aspects in narcolepsy with cataplexy (59%) than in narcolepsy without cataplexy (28%) and PD (26%). Compared to PD, the hallucinations in narcolepsy were less frequently of the passage/presence type (passage: brief visions of a person or animal passing sideways; presence: perception that a living character or an animal is behind or near the subject, without the subject actually seeing, hearing or touching it), more frequently auditory and more often associated with sleep. However, in 40% of the patients with narcolepsy and 54% of the patients with PD, the hallucinations occurred while the patients were wide awake. Patients with cataplexy had reduced immediate insight into the unreality of their hallucinations compared to patients with PD, but the delusions were exceptional (2%), transient and based on hallucinations in both groups. The risk factors for hallucinations were sleep paralysis and RBD in narcolepsy and motor disability and sleepiness in PD.

CONCLUSIONS

The multimodal, dreamlike aspect of hallucinations in narcolepsy with cataplexy could transiently impair the patients' insight. The high frequency of these hallucinations (compared to those in narcolepsy without cataplexy or PD) suggests that complete (more than partial) hypocretin-1 deficiency promotes hallucinations.

Phasic motor activity of respiratory and non-respiratory muscles in REM sleep

OBJECTIVES

In this study, we quantified the profiles of phasic activity in respiratory muscles (diaphragm, genioglossus and external intercostal) and non-respiratory muscles (neck and extensor digitorum) across REM sleep. We hypothesized that if there is a unique pontine structure that controls all REM sleep phasic events, the profiles of the phasic twitches of different muscle groups should be identical. Furthermore, we described how respiratory parameters (e.g., frequency, amplitude, and effort) vary across REM sleep to determine if phasic processes affect breathing.

METHODS

Electrodes were implanted in Wistar rats to record brain activity and muscle activity of neck, extensor digitorum, diaphragm, external intercostal, and genioglossal muscles. Ten rats were studied to obtain 313 REM periods over 73 recording days. Data were analyzed offline and REM sleep activity profiles were built for each muscle. In 6 animals, respiratory frequency, effort, amplitude, and inspiratory peak were also analyzed during 192 REM sleep periods.

RESULTS

Respiratory muscle phasic activity increased in the second part of the REM period. For example, genioglossal activity increased in the second part of the REM period by 63.8% compared to the average level during NREM sleep. This profile was consistent between animals and REM periods (η(2)=0.58). This increased activity seen in respiratory muscles appeared as irregular bursts and trains of activity that could affect rythmo-genesis. Indeed, the increased integrated activity seen in the second part of the REM period in the diaphragm was associated with an increase in the number (28.3%) and amplitude (30%) of breaths. Non-respiratory muscle phasic activity in REM sleep did not have a profile like the phasic activity of respiratory muscles. Time in REM sleep did not have an effect on nuchal activity (P=0.59).

CONCLUSION

We conclude that the concept of a common pontine center controlling all REM phasic events is not supported by our data. There is a drive in REM sleep that affects specifically respiratory muscles. The characteristic increase in respiratory frequency during REM sleep is induced by this drive.

Eye movements and abducens motoneuron behavior after cholinergic activation of the nucleus reticularis pontis caudalis

STUDY OBJECTIVES

the aim of this work was to characterize eye movements and abducens (ABD) motoneuron behavior after cholinergic activation of the nucleus reticularis pontis caudalis (NRPC).

METHODS

six female adult cats were prepared for chronic recording of eye movements (using the scleral search-coil technique), electroencephalography, electromyography, ponto-geniculo-occipital (PGO) waves in the lateral geniculate nucleus, and ABD motoneuron activities after microinjections of the cholinergic agonist carbachol into the NRPC.

RESULTS

unilateral microinjections of carbachol in the NRPC induced tonic and phasic phenomena in the oculomotor system. Tonic effects consisted of ipsiversive rotation to the injected side, convergence, and downward rotation of the eyes. Phasic effects consisted of bursts of rhythmic rapid eye movements directed contralaterally to the injected side along with PGO-like waves in the lateral geniculate and ABD nuclei. Although tonic effects were dependent on the level of drowsiness, phasic effects were always present and appeared along with normal saccades when the animal was vigilant. ABD motoneurons showed phasic activities associated with ABD PGO-like waves during bursts of rapid eye movements, and tonic and phasic activities related to eye position and velocity during alertness.

CONCLUSION

the cholinergic activation of the NRPC induces oculomotor phenomena that are somewhat similar to those described during REM sleep. A precise comparison of the dynamics and timing of the eye movements further suggests that a temporal organization of both NRPCs is needed to reproduce the complexity of the oculomotor behavior during REM sleep.

Do the eyes scan dream images during rapid eye movement sleep? Evidence from the rapid eye movement sleep behaviour disorder model

Rapid eye movements and complex visual dreams are salient features of human rapid eye movement sleep. However, it remains to be elucidated whether the eyes scan dream images, despite studies that have retrospectively compared the direction of rapid eye movements to the dream recall recorded after having awakened the sleeper. We used the model of rapid eye movement sleep behaviour disorder (when patients enact their dreams by persistence of muscle tone) to determine directly whether the eyes move in the same directions as the head and limbs. In 56 patients with rapid eye movement sleep behaviour disorder and 17 healthy matched controls, the eye movements were monitored by electrooculography in four (right, left, up and down) directions, calibrated with a target and synchronized with video and sleep monitoring. The rapid eye movement sleep behaviour disorder-associated behaviours occurred 2.1 times more frequently during rapid eye movement sleep with than without rapid eye movements, and more often during or after rapid eye movements than before. Rapid eye movement density, index and complexity were similar in patients with rapid eye movement sleep behaviour disorder and controls. When rapid eye movements accompanied goal-oriented motor behaviour during rapid eye movement sleep behaviour disorder (e.g. grabbing a fictive object, hand greetings, climbing a ladder), which happened in 19 sequences, 82% were directed towards the action of the patient (same plane and direction). When restricted to the determinant rapid eye movements, the concordance increased to 90%. Rapid eye movements were absent in 38-42% of behaviours. This directional coherence between limbs, head and eye movements during rapid eye movement sleep behaviour disorder suggests that, when present, rapid eye movements imitate the scanning of the dream scene. Since the rapid eye movements are similar in subjects with and without rapid eye movement sleep behaviour disorder, this concordance can be extended to normal rapid eye movement sleep.

The development of the science of dreaming

Although the main peripheral features of dreaming were identified two millennia ago, the neurobiological study of the basic and higher integrated processes underlying rapid eye movement (REM) sleep only began about 70 years ago. Today, the combined contributions of the successive and complementary methods of electrophysiology, imaging, pharmacology, and neurochemistry have provided a good level of knowledge of the opposite but complementary activating and inhibitory processes which regulate waking mentation and which are disturbed during REM sleep, inducing a schizophrenic-like mental activity.

Evidence of subthalamic PGO-like waves during REM sleep in humans: a deep brain polysomnographic study

STUDY OBJECTIVES

The aim of this study was to examine whether the subthalamic nucleus (STN) plays a role in the transmission of PGO-like waves during REM sleep in humans.

DESIGN

Simultaneous recordings from deep brain electrodes to record local field potentials (LFPs), and standard polysomnography to ascertain sleep/wake states.

SETTING

Main Hospital, department of clinical neurophysiology sleep laboratory.

PARTICIPANTS

12 individuals with Parkinson's disease, with electrodes implanted in the STN; and, as a control for localization purposes, 4 cluster headache patients with electrodes implanted in the posterior hypothalamus.

INTERVENTIONS

All subjects underwent functional neurosurgery for implantation of deep brain stimulation electrodes.

RESULTS

Sharp, polarity-reversed LFPs were recorded within the STN during REM sleep in humans. These subthalamic PGO-like waves (2-3 Hz, 80-200 pV, and 300-500 msec) appeared during REM epochs as singlets or in clusters of 3-13 waves. During the pre-REM period, subthalamic PGO-like waves were temporally related to drops in the submental electromyogram and/or onset of muscular atonia. Clusters of PGO-like waves occurred typically before and during the bursts of rapid eye movements and were associated with an enhancement in fast (15-35 Hz) subthalamic oscillatory activity.

CONCLUSION

Subthalamic PGO-like waves can be recorded during pre-REM and REM sleep in humans. Our data suggest that the STN may play an active role in an ascending activating network implicated in the transmission of PGO waves during REM sleep in humans.

Neural generators of brain potentials before rapid eye movements during human REM sleep: a study using sLORETA

OBJECTIVE

Brain activity preceding rapid eye movements (REM) during human REM sleep has remained poorly understood. Slow negative brain potential (pre-REM negativity) appears before REMs. Current sources of this potential were investigated to identify brain activity immediately preceding REMs.

METHODS

In this study, 22 young healthy volunteers (20-25 years old) participated. Polysomnograms were recorded during normal nocturnal sleep. Brain potentials between 200ms before and 50ms after the onset of REMs and pseudo-triggers (3000ms before the onset of REMs) were averaged. Standardized low-resolution brain electromagnetic tomography (sLORETA) was used to estimate current sources of pre-REM negativity.

RESULTS

Pre-REM negativity appeared with the maximal amplitude at right prefrontal sites immediately before REMs. However, this negativity did not appear before pseudo-triggers. Current sources of the pre-REM negativity were estimated in the ventromedial prefrontal cortex, uncus, insula, anterior cingulated cortex, basal forebrain, parahippocampal gyrus, premotor cortex and frontal eye field.

CONCLUSIONS

The pre-REM negativity reflects brain activity coupled with the occurrence of REMs. Results of this study suggest that emotion, memory, and motor-related brain activity might occur before REMs.

SIGNIFICANCE

Pre-REM negativity is expected to be a psychophysiological index for elucidating functions of REM sleep.

Brain activity and temporal coupling related to eye movements during REM sleep: EEG and MEG results

EEG and MEG REM sleep gamma activity was studied immediately before rapid eye movement onset (PRE-EM), during REM sleep with eye movements away from eye movement onset -phasic-REM (Ph-REM)--and during REM sleep without eye movements, or tonic REM (T-REM). For this purpose, activity was segmented into three different time windows: of 62.5, 250 and 500 ms. Two strategies were used: one a statistical comparison of changes between T-REM, Ph-REM and PRE-EM; the other a descriptive approach using principal component analysis. Significant findings showed that both EEG and MEG gamma activity are higher directly before eye movement onset in PRE-EM periods and during Ph-REM than during T-REM; temporal coupling of electrical activity between the frontal and parietal regions is decreased, while temporal coupling between the right frontal and midline is increased. Just before eye movement onset, larger recording sites become related. For the first time, results showed a close temporal link between power and temporal coupling of fast oscillations andrapid eye movements in REM sleep, indicating increased activation, uncoupling between the left frontal executive areas and posterior sensory association regions and increased coupling between the right frontal attentional and midline alerting systems. Brain activity is reorganized by phasic events.

Tonic and phasic phenomena underlying eye movements during sleep in the cat

Mammalian sleep is not a homogenous state, and different variables have traditionally been used to distinguish different periods during sleep. Of these variables, eye movement is one of the most paradigmatic, and has been used to differentiate between the so-called rapid eye movement (REM) and non-REM (NREM) sleep periods. Despite this, eye movements during sleep are poorly understood, and the behaviour of the oculomotor system remains almost unknown. In the present work, we recorded binocular eye movements during the sleep-wake cycle of adult cats by the scleral search-coil technique. During alertness, eye movements consisted of conjugated saccades and eye fixations. During NREM sleep, eye movements were slow and mostly unconjugated. The two eyes moved upwardly and in the abducting direction, producing a tonic divergence and elevation of the visual axis. During the transition period between NREM and REM sleep, rapid monocular eye movements of low amplitude in the abducting direction occurred in coincidence with ponto-geniculo-occipital waves. Along REM sleep, the eyes tended to maintain a tonic convergence and depression, broken by high-frequency bursts of complex rapid eye movements. In the horizontal plane, each eye movement in the burst comprised two consecutive movements in opposite directions, which were more evident in the eye that performed the abducting movements. In the vertical plane, rapid eye movements were always upward. Comparisons of the characteristics of eye movements during the sleep-wake cycle reveal the uniqueness of eye movements during sleep, and the noteworthy existence of tonic and phasic phenomena in the oculomotor system, not observed until now.

The developmental decrease in REM sleep: the role of transmitters and electrical coupling

STUDY OBJECTIVES

This mini-review considers certain factors related to the developmental decrease in rapid eye movement (REM) sleep, which occurs in favor of additional waking time, and its relationship to developmental factors that may influence its potential role in brain development.

DESIGN

Specifically, we discuss some of the theories proposed for the occurrence of REM sleep and agree with the classic notion that REM sleep is, at the least, a mechanism that may play a role in the maturation of thalamocortical pathways. The developmental decrease in REM sleep occurs gradually from birth until close to puberty in the human, and in other mammals it is brief and coincides with eye and ear opening and the beginning of massive exogenous activation. Therefore, the purported role for REM sleep may change to involve a number of other functions with age.

MEASUREMENTS AND RESULTS

We describe recent findings showing that morphologic and physiologic properties as well as cholinergic, gamma amino-butyric acid, kainic acid, n-methyl-d-aspartic acid, noradrenergic, and serotonergic synaptic inputs to mesopontine cholinergic neurons, as well as the degree of electrical coupling between mostly noncholinergic mesopontine neurons and levels of the neuronal gap-junction protein connexin 36, change dramatically during this critical period in development. A novel mechanism for sleep-wake control based on well-known transmitter interactions, as well as electrical coupling, is described.

CONCLUSION

We hypothesize that a dysregulation of this process could result in life-long disturbances in arousal and REM sleep drive, leading to hypervigilance or hypovigilance such as that observed in a number of disorders that have a mostly postpubertal age of onset.

Evidence for Electrical Coupling in the SubCoeruleus (SubC) Nucleus

SubCoeruleus (SubC) neurons, which are thought to modulate rapid-eye-movement (REM) sleep, were recorded in brain stem slices from 7- to 20-day rats and found to manifest spikelets, indicative of electrical coupling. Spikelets occurred spontaneously or could be induced by superfusion of the cholinergic agonist carbachol. Whole cell recordings revealed that carbachol induced membrane oscillations and spikelets in the theta frequency range in SubC neurons in the presence of fast synaptic blockers. Electrical coupling in neurons is mediated by the gap junction protein connexin 36 (Cx 36). We found that Cx 36 gene expression and protein in the mesopontine tegmentum decreased during development. Cx 36 protein levels specifically in the SubC decreased in concert with the developmental decrease in REM sleep. The presence of electrical coupling in the SubC introduces a novel potential mechanism of action for the regulation of sleep-wake states.

Electrophysiological characterization of neurons in the dorsolateral pontine rapid-eye-movement sleep induction zone of the rat: Intrinsic membrane properties and responses to carbachol and orexins

Pharmacological, lesion and single-unit recording techniques in several animal species have identified a region of the pontine reticular formation (subcoeruleus, SubC) just ventral to the locus coeruleus as critically involved in the generation of rapid-eye-movement (REM) sleep. However, the intrinsic membrane properties and responses of SubC neurons to neurotransmitters important in REM sleep control, such as acetylcholine and orexins/hypocretins, have not previously been examined in any animal species and thus were targeted in this study. We obtained whole-cell patch-clamp recordings from visually identified SubC neurons in rat brain slices in vitro. Two groups of large neurons (mean diameter 30 and 27 mum) were tentatively identified as cholinergic (rostral SubC) and noradrenergic (caudal SubC) neurons. SubC reticular neurons (non-cholinergic, non-noradrenergic) showed a medium-sized depolarizing sag during hyperpolarizing current pulses and often had a rebound depolarization (low-threshold spike, LTS). During depolarizing current pulses they exhibited little adaptation and fired maximally at 30-90 Hz. Those SubC reticular neurons excited by carbachol (n=27) fired spontaneously at 6 Hz, often exhibited a moderately sized LTS, and varied widely in size (17-42 mum). Carbachol-inhibited SubC reticular neurons were medium-sized (15-25 mum) and constituted two groups. The larger group (n=22) was silent at rest and possessed a prominent LTS and associated one to four action potentials. The second, smaller group (n=8) had a delayed return to baseline at the offset of hyperpolarizing pulses. Orexins excited both carbachol excited and carbachol inhibited SubC reticular neurons. SubC reticular neurons had intrinsic membrane properties and responses to carbachol similar to those described for other reticular neurons but a larger number of carbachol inhibited neurons were found (>50%), the majority of which demonstrated a prominent LTS and may correspond to pontine-geniculate-occipital burst neurons. Some or all carbachol-excited neurons are presumably REM-on neurons.

Orexinergic projections to the cat midbrain mediate alternation of emotional behavioural states from locomotion to cataplexy

Orexinergic neurones in the perifornical lateral hypothalamus project to structures of the midbrain, including the substantia nigra and the mesopontine tegmentum. These areas contain the mesencephalic locomotor region (MLR), and the pedunculopontine and laterodorsal tegmental nuclei (PPN/LDT), which regulate atonia during rapid eye movement (REM) sleep. Deficiencies of the orexinergic system result in narcolepsy, suggesting that these projections are concerned with switching between locomotor movements and muscular atonia. The present study characterizes the role of these orexinergic projections to the midbrain. In decerebrate cats, injecting orexin-A (60 microm to 1.0 mm, 0.20-0.25 microl) into the MLR reduced the intensity of the electrical stimulation required to induce locomotion on a treadmill (4 cats) or even elicit locomotor movements without electrical stimulation (2 cats). On the other hand, when orexin was injected into either the PPN (8 cats) or the substantia nigra pars reticulata (SNr, 4 cats), an increased stimulus intensity at the PPN was required to induce muscle atonia. The effects of orexin on the PPN and the SNr were reversed by subsequently injecting bicuculline (5 mm, 0.20-0.25 microl), a GABA(A) receptor antagonist, into the PPN. These findings indicate that excitatory orexinergic drive could maintain a higher level of locomotor activity by increasing the excitability of neurones in the MLR, while enhancing GABAergic effects on presumably cholinergic PPN neurones, to suppress muscle atonia. We conclude that orexinergic projections from the hypothalamus to the midbrain play an important role in regulating motor behaviour and controlling postural muscle tone and locomotor movements when awake and during sleep. Furthermore, as the excitability is attenuated in the absence of orexin, signals to the midbrain may induce locomotor behaviour when the orexinergic system functions normally but elicit atonia or narcolepsy when the orexinergic function is disturbed.

Instantaneous acceleration and amplification of hippocampal theta wave coincident with phasic pontine activities during REM sleep

Rapid eye movement (REM) sleep is characterized by hippocampal theta waves and phasic spike-like waves originating from the pons, termed ponto-geniculo-occipital (PGO) waves in cats and pontine (P) waves in rats. While the theta wave and PGO/P wave have been suggested to participate in higher-order brain functions, their generation mechanisms and roles in brain functions have been studied independently. Therefore, the present study investigated instantaneous aspects of the relationship between theta waves and PGO/P waves in both cats and rats. Theta wave was instantaneously accelerated several hundred milliseconds before the negative peak of the PGO/P wave in both animals, and was also amplified just before PGO/P wave occurrence. Considering the integrated knowledge provided by studies of both animals, these results suggest that PGO/P wave-related activities in the pons are delivered to the theta wave generator. The activations of the theta wave coincident with PGO/P wave might facilitate cooperative contribution to higher-order brain functions in REM sleep.

Theta wave amplitude and frequency are differentially correlated with pontine waves and rapid eye movements during REM sleep in rats

The present study examined the correlations between the dynamics of hippocampal theta waves and pontine waves (P waves) and rapid eye movements (REMs) densities during REM sleep. Theta wave peak frequency and theta amplitude were estimated as the parameters of theta wave dynamics in each 3s segment. The peak frequency and theta amplitude were positively correlated with P wave and REMs densities, however their detailed correlation properties were distinct from each other. Dependency of peak frequency on P wave/REMs density did not change significantly from that on REMs/P wave density. On the other hand, dependency of the theta amplitude on P wave/REMs density significantly increased with an increased REMs/P wave density. Because hippocampal theta waves and P waves are involved in learning and memory functions during REM sleep, the correlation between theta parameters and P wave density might help to clarify these functions.

Role of basal ganglia–brainstem pathways in the control of motor behaviors

Here we review a role of a basal ganglia-brainstem (BG-BS) system throughout the mesopontine tegmentum in the control of various types of behavioral expression. First the basal ganglia-brainstem system may contribute to an automatic control of movements, such as rhythmic limb movements and adjustment of postural muscle tone during locomotion, which occurs in conjunction with voluntary control processes. Second, the basal ganglia-brainstem system can be involved in the regulation of awake-sleep states. We further propose the possibility that the basal ganglia-brainstem system is responsible for the integration of volitionally-guided and emotionally-triggered expression of motor behaviors. It can be proposed that dysfunction of the basal ganglia-brainstem system together with that of cortico-basal ganglia loop underlies the pathogenesis of behavioral disturbances expressed in basal ganglia dysfunction.

Evidence for a role of basal ganglia in the regulation of rapid eye movement sleep by electrical and chemical stimulation for the pedunculopontine tegmental nucleus and the substantia nigra pars reticulata in decerebrate cats

The present study was to determine how afferents from the substantia nigra pars reticulata (SNr) of the basal ganglia to the pedunculopontine tegmental nucleus (PPN) in the brainstem could contribute to the control of behavioral states. We used anesthetized and acutely decerebrated cats (n=22). Repetitive electrical stimulation (10-100 Hz, 20-50 microA, for 4-20 s) to the ventrolateral part of the PPN produced rapid eye movement (REM) associated with a suppression of postural muscle tone (REM with atonia). Although repetitive electrical stimuli (10-200 Hz, 10-60 microA, for 5-20 s) delivered to the dorsolateral part of the SNr did not evoke eye movements or muscular tonus in baseline conditions, it altered the PPN-induced REM with atonia. The following three types of effects were induced: (1) attenuation of the REM with atonia; (2) attenuation of muscular atonia without changes in REM (REM without atonia); and (3) attenuation of only REM. The optimal stimulus sites for these effects were intermingled within the lateral part of the SNr. The PPN-induced REM with atonia was abolished by an injection into the PPN of muscimol (1-15 mM, 0.1-0.25 microl), a GABAA receptor agonist, but not altered by an injection of baclofen (1-10 mM, 0.1-0.25 microl), a GABAB receptor agonist. Moreover, an injection of bicuculline (1-15 mM, 0.1-0.25 microl), a GABAA receptor antagonist, into the PPN, resulted in REM with atonia. On the other hand, an injection of muscimol into the dorsolateral part of the SNr (1-15 mM, 0.1-0.25 microl) induced REM with atonia, which was in turn eliminated by a further injection of muscimol into the PPN (5-10 mM, 0.2-0.25 microl). These results suggest that a GABAergic projection from the SNr to the PPN could be involved in the control of REM with atonia, signs which indicate REM sleep. An excessive GABAergic output from the basal ganglia to the PPN in parkinsonian patients may induce sleep disturbances, including a reduction of REM sleep periods and REM sleep behavioral disorders (REM without atonia).

Phase-locking of spontaneous and elicited ponto-geniculo-occipital waves is associated with acceleration of hippocampal theta waves during rapid eye movement sleep in cats

We investigated the temporal relationship between hippocampal theta waves and ponto-geniculo-occipital waves (PGO) during rapid eye movement sleep (REM sleep) in cats. In addition, we analyzed the relationship between hippocampal theta waves and PGO as elicited by tone stimulus (PGO(E)) in order to quantitively characterize the PGO wave generator mechanism. The results showed that a spontaneous PGO tended to be phase-locked to the theta wave, which was more clearly observed in the single PGO than in the cluster. However, cluster PGO(E) tended to be phase-locked as well as single PGO(E). It was therefore suggested that the generator of PGO is activated in relation to the hippocampal theta wave. An acceleration of the theta wave associated with PGO occurrence was found, and was more markedly observed than with the cluster PGO. Although the magnitude of it was less than in the spontaneous case, an acceleration around the PGO(E) was also observed. These results suggest that the generators of theta and PGO receive some common activations, especially when a cluster PGO is generated. The interaction between PGO and hippocampal theta waves is expected to be involved in the possible functions of REM sleep.

The golden age of rapid eye movement sleep discoveries. 1. Lucretius--1964

Although there were several premonitory signs of a sleep stage with dreaming, it was only in 1953 that such a stage was identified with certainty. This paper analyses the observations and research related to this dreaming stage (rapid eye movement sleep) until 1964. During these 11 years of research, the main psychological and physiological characteristics of this sleep stage were first described. Where the few results or discussions were later questioned, today's current state of knowledge is briefly outlined.

Generation of rapid eye movements during paradoxical sleep in humans

Although rapid eye movements (REMs) are a prominent feature of paradoxical sleep (PS), their origin and functional significance remain poorly understood in humans. In animals, including nonhuman primates, REMs during PS are closely related to the occurrence of the so-called PGO waves, i.e., prominent phasic activities recorded throughout the brain but predominantly and most easily in the pons (P), the lateral geniculate bodies (G), and the occipital cortex (O). Therefore, and because the evolution of species is parsimonious, a plausible hypothesis would be that during PS in humans, REMs are generated by mechanisms similar to PGO waves. Using positron emission tomography and iterative cerebral blood flow measurements by H(2)(15)O infusions, we predicted that the brain regions where the PGO waves are the most easily recorded in animals would be differentially more active in PS than in wakefulness, in relation with the density of the REM production [i.e., we looked for the condition (PS versus wakefulness) by performance (REM density) interaction]. Accordingly, we found a significant interaction effect in the right geniculate body and in the primary occipital cortex. The result supports the hypothesis of the existence of processes similar to PGO waves in humans, responsible for REM generation. The interest in the presence of PGO waves in humans is outstanding because the cellular processes involved in, or triggered by, PGO waves might favor brain plasticity during PS.