Varying expressions of alerting mechanisms in wakefulness and across sleep states

Rostral Intralaminar Thalamus Engagement in Cognition and Behavior

The thalamic rostral intralaminar nuclei (rILN) are a contiguous band of neurons that include the central medial, paracentral, and central lateral nuclei. The rILN differ from both thalamic relay nuclei, such as the lateral geniculate nucleus, and caudal intralaminar nuclei, such as the parafascicular nucleus, in afferent and efferent connectivity as well as physiological and synaptic properties. rILN activity is associated with a range of neural functions and behaviors, including arousal, pain, executive function, and action control. Here, we review this evidence supporting a role for the rILN in integrating arousal, executive and motor feedback information. In light of rILN projections out to the striatum, amygdala, and sensory as well as executive cortices, we propose that such a function enables the rILN to modulate cognitive and motor resources to meet task-dependent behavioral engagement demands.

The pulse: transient fMRI signal increases in subcortical arousal systems during transitions in attention

Studies of attention emphasize cortical circuits for salience monitoring and top-down control. However, subcortical arousal systems have a major influence on dynamic cortical state. We hypothesize that task-related increases in attention begin with a "pulse" in subcortical arousal and cortical attention networks, which are reflected indirectly through transient fMRI signals. We conducted general linear model and model-free analyses of fMRI data from two cohorts and tasks with mixed block and event-related design. 46 adolescent subjects at our center and 362 normal adults from the Human Connectome Project participated. We identified a core shared network of transient fMRI increases in subcortical arousal and cortical salience/attention networks across cohorts and tasks. Specifically, we observed a transient pulse of fMRI increases both at task block onset and with individual task events in subcortical arousal areas including midbrain tegmentum, thalamus, nucleus basalis and striatum; cortical-subcortical salience network regions including the anterior insula/claustrum and anterior cingulate cortex/supplementary motor area; in dorsal attention network regions including dorsolateral frontal cortex and inferior parietal lobule; as well as in motor regions including cerebellum, and left hemisphere hand primary motor cortex. The transient pulse of fMRI increases in subcortical and cortical arousal and attention networks was consistent across tasks and study populations, whereas sustained activity in these same networks was more variable. The function of the transient pulse in these networks is unknown. However, given its anatomical distribution, it could participate in a neuromodulatory surge of activity in multiple parallel neurotransmitter systems facilitating dynamic changes in conscious attention.

Filtering the reality: functional dissociation of lateral and medial pain systems during sleep in humans

Behavioral reactions to sensory stimuli during sleep are scarce despite preservation of sizeable cortical responses. To further understand such dissociation, we recorded intracortical field potentials to painful laser pulses in humans during waking and all-night sleep. Recordings were obtained from the three cortical structures receiving 95% of the spinothalamic cortical input in primates, namely the parietal operculum, posterior insula, and mid-anterior cingulate cortex. The dynamics of responses during sleep differed among cortical sites. In sleep Stage 2, evoked potential amplitudes were similarly attenuated relative to waking in all three cortical regions. During paradoxical, or rapid eye movements (REM), sleep, opercular and insular potentials remained stable in comparison with Stage 2, whereas the responses from mid-anterior cingulate abated drastically, and decreasing below background noise in half of the subjects. Thus, while the lateral operculo-insular system subserving sensory analysis of somatic stimuli remained active during paradoxical-REM sleep, mid-anterior cingulate processes related to orienting and avoidance behavior were suppressed. Dissociation between sensory and orienting-motor networks might explain why nociceptive stimuli can be either neglected or incorporated into dreams without awakening the subject.

Central thalamic contributions to arousal regulation and neurological disorders of consciousness

This review focuses on the contributions of the central thalamus to normal mechanisms of arousal regulation and to neurological disorders of consciousness. Forebrain arousal is regulated by ascending influences from brainstem/basal forebrain neuronal populations ("arousal systems") and control signals descending from frontal cortical systems. These subcortical and cortical systems have converging projections to the central thalamus that emphasize their role in maintaining organized behavior during wakefulness. Central thalamic neurons appear to be specialized both anatomically and physiologically to support distributed network activity that maintains neuronal firing patterns across long-range cortico-cortical pathways and within cortico-striatopallidal-thalamocortical loop connections. Recruitment of central thalamic neurons occurs in response to increasing cognitive demand, stress, fatigue, and other perturbations that reduce behavioral performance. In addition, the central thalamus receives projections from brainstem pathways evolved to rapidly generate brief shifts of arousal associated with the appearance of salient stimuli across different sensory modalities. Through activation of the central thalamus, neurons across the cerebral cortex and striatum can be depolarized and their activity patterns selectively gated by descending or ascending signals related to premotor attention and alerting stimuli. Direct injury to the central thalamus or prominent deafferentation of these neurons as a result of complex, multifocal, brain insults are both associated with severe impairment of forebrain functional integration and arousal regulation. Interventions targeting neurons within the central thalamus may lead to rational therapeutic approaches to the treatment of impaired arousal regulation following nonprogressive brain injuries. A model accounting for present therapeutic strategies is proposed.

Effects of tetrodotoxin (TTX) inactivation of the central nucleus of the amygdala (CNA) on dark period sleep and activity

The amygdala has been implicated in emotional arousal and in the regulation of sleep. Previously, we demonstrated that tetrodotoxin (TTX), a sodium channel blocker that temporarily inactivates neurons and tracts, microinjected into the central nucleus of the amygdala (CNA) during the light period significantly reduced REM, shortened sleep latency, and increased EEG delta power in rats. TTX inactivation of CNA also reduced activity in the open field. These findings suggest that the amygdala modulates arousal in a variety of situations. To test the hypothesis that the amygdala may influence spontaneous arousal, we examined the effects of TTX inactivation of CNA on sleep and activity during the dark period when rats show higher arousal and less sleep. EEG and activity were recorded via telemetry in Wistar rats (n = 8). Bilateral microinjections of TTX (L: 2.5 ng/0.1; H: 5.0 ng/0.2 microl) or SAL (saline, 0.2 microl) were administered before lights off followed by recording throughout the 12-h dark period and following 12-h light period. Microinjections were given at 5-day intervals and were counterbalanced across condition. TTX significantly shortened sleep latency, increased NREM time, decreased REM time, and decreased activity. TTX increased NREM episode duration, whereas the number and duration of REM episodes were decreased. The present results indicate that TTX inactivation of CNA can increase NREM time when spontaneous arousal is high, suggesting a broad role for the amygdala in regulating arousal. The results suggest that understanding the ways in which the amygdala modulates arousal may provide insight into the mechanisms underlying altered sleep in mood and anxiety disorders.

Cholinergic regulation of the central nucleus of the amygdala in rats: Effects of local microinjections of cholinomimetics and cholinergic antagonists on arousal and sleep

The amygdala has emerged as an important forebrain modulator of arousal. Acetylcholine plays a role in the regulation of sleep and wakefulness, particularly rapid eye movement sleep (REM). The major cholinergic input to the amygdala comes from the basal forebrain, a region primarily linked to wakefulness. We examined sleep and the encephalogram for 8 h following bilateral microinjections into the central nucleus of the amygdala (CNA) of the cholinergic agonist, carbachol (CARB(L): 0.3 microg; CARB(H): 3.0 microg), the acetylcholinesterase inhibitor, neostigmine (NEO(L): 0.3 microg; NEO(H): 3.0 microg), the muscarinic antagonist, scopolamine (SCO(L): 0.3 microg; SCO(H): 1.0 microg), the nicotinic antagonist, mecamylamine (MEC(L): 0.3 microg; MEC(H): 1.0 microg) and saline (SAL, 0.2 microl) alone. Both doses of CARB and NEO significantly reduced REM, but did not significantly alter non-rapid eye movement sleep (NREM). Both doses of SCO significantly increased NREM, and SCO(H) also produced an initial increase in REM followed by a significant decrease. CARB(H) and NEO(H) decreased REM electroencephalogram (EEG) power in the 5.5-10 Hz band, and NEO(L) and NEO(H) decreased NREM EEG power in the 0.5-5.0 Hz band. CARB(L) decreased waking EEG power in the 0.5-5.0 Hz band, and NEO(H) decreased waking EEG power in the 5.0-10.0 Hz band. Both doses of SCO significantly increased waking EEG power in the 5.5-10.0 Hz band. Compared with SAL, MEC did not significantly alter sleep or EEG power. The reduction of REM by CARB and NEO and the alteration of sleep by SCO indicate that cholinergic regulation of the amygdala is involved in the control of arousal in rodents. In contrast, CARB microinjections into CNA increase REM in cats, though the reasons for the species difference are not known. The results are discussed in the context of anatomical inputs and species differences in the cholinergic regulation of CNA.

Spontaneous eyelid movements (ELMS) during sleep are related to dream recall on awakening

The present study aimed to test whether spontaneous eyelid movements (ELMs) during stage 2 and rapid eye movement (REM) sleep are related to more frequent and vivid reports of visual mentation on awakening. Participants were awakened 15 s after an ELM was observed during ongoing REM and stage 2 sleep and immediately asked for a mentation report and to rate the visual vividness of any imagery they could remember. These reports were compared with control reports collected after a period of ELM quiescence before awakening (noELM). Significantly greater frequencies of imagery reports were collected after ELM awakenings compared with noELM awakenings from stage 2, but not REM sleep. When imagery was reported, imagery ratings were not significantly different between ELM and noELM conditions, regardless of sleep stage. The average amount of electroencephalogram (EEG) arousal 15 s after stage 2 awakenings was significantly higher in the ELM compared with noELM conditions. In addition, within the stage 2 ELM condition, EEG arousal was significantly higher when visual imagery was reported compared with reports without imagery; suggesting that the observed increase in imagery reporting from the stage 2 ELM condition could have been mediated by the level of brain arousal. Such arousal possibly provides better conditions to attend and recall previous mental activity from NREM sleep. However, there was no ELM/arousal effect within REM sleep, possibly because this state is already at maximum sleeping levels of arousal, attention and resulting dream recall.

Decreased arousals among healthy infants after short-term sleep deprivation

OBJECTIVE

Sleep deprivation is a risk factor for sudden infant death syndrome (SIDS). Recent changes in normal life routines were more common among SIDS victims, compared with control infants. Sleep deprivation can result from handling conditions or from sleep fragmentation attributable to respiratory or digestive conditions, fever, or airway obstructions during sleep. Compared with matched control infants, future SIDS victims exhibited fewer complete arousals by the end of the night, when most SIDS cases occur. Arousal from sleep could be an important defense against potentially dangerous situations during sleep. Because the arousal thresholds of healthy infants were increased significantly under conditions known to favor SIDS, we evaluated the effects of a brief period of sleep deprivation on sleep and arousal characteristics of healthy infants.

DESIGN

Fourteen healthy infants, with a median age of 8 weeks (range: 6-18 weeks), underwent polygraphic recording during a morning nap and an afternoon nap, in a sleep laboratory. The infants were sleep-deprived for 2 hours before being allowed to fall asleep. Sleep deprivation was achieved by keeping the infants awake, with playing, handling, and mild tactile or auditory stimulations, for as long as possible beyond their habitual bedtimes. To avoid any confounding effect attributable to differences in sleep tendencies throughout the day, sleep deprivation was induced before either the morning nap or the afternoon nap. Seven infants were sleep-deprived before the morning nap and 7 before the afternoon nap. The sleep and arousal characteristics of each infant were compared for the non-sleep-deprived condition (normal condition) and the sleep-deprived condition. During each nap, the infants were exposed, during rapid eye movement (REM) sleep, to white noise of increasing intensity, from 50 dB(A) to 100 dB(A), to determine their arousal thresholds. Arousal thresholds were defined on the basis of the lowest auditory stimuli needed to induce arousal. After the induced arousal, the infants were allowed to return to sleep to complete their naps.

RESULTS

Sleep deprivation lasted a median of 120 minutes (range: 90-272 min). Most sleep characteristics were similar for the normal and sleep-deprived conditions, including sleep efficiency, time awake, percentages of REM sleep and non-REM sleep, frequency and duration of central apnea and of periodic breathing, duration of obstructive apnea, mean heart rate and variability, and mean breathing rates during REM sleep and non-REM sleep. After sleep deprivation, the duration of the naps increased, whereas there were decreases in the latency of REM sleep and in the density of body movements. More-intense auditory stimuli were needed for arousal when the infants were sleep-deprived, compared with normal nap sleep. Sleep deprivation was associated with a significant increase in the frequency of obstructive sleep apnea episodes, especially during REM sleep. No significant differences were noted when the effects of morning and afternoon sleep deprivation were compared. No correlation was found between the duration of sleep deprivation and either the frequency of obstructive apnea or the changes in arousal thresholds, although the infants who were more sleep-deprived exhibited tendencies toward higher auditory arousal thresholds and shorter REM sleep latencies, compared with less sleep-deprived infants. There were tendencies for a negative correlation between the auditory arousal thresholds and REM sleep latencies and for a positive correlation between the auditory arousal thresholds and the frequencies of obstructive apnea during REM sleep.

CONCLUSIONS

Short-term sleep deprivation among infants is associated with the development of obstructive sleep apnea and significant increases in arousal thresholds. As already reported, sleep deprivation may induce effects on respiratory control mechanisms, leading to impairment of ventilatory and arousal responses to chemical stimulation and decreases in genioglossal electromyographic activity during REM sleep. These changes in respiratory control mechanisms could contribute to the development of obstructive apnea. The relationship between the development of obstructive apnea and increases in arousal thresholds remains to be evaluated. Adult subjects with obstructive sleep apnea exhibited both sleep fragmentation and increases in arousal thresholds. Conversely, sleep deprivation increased the frequency and severity of obstructive sleep apnea. In this study, the increases in arousal thresholds and the development of obstructive apnea seemed to result from the preceding sleep deprivation. The depressed arousals that follow sleep deprivation have been attributed to central mechanisms, rather than decreases in peripheral sensory organ function. Such mechanisms could include disturbances within the reticular formation of the brainstem, which integrates specific facilitory inputs, such as ascending pathways from auditory receptors, and inhibitory inputs from the cortex. It remains to be determined whether the combination of upper airway obstruction and depressed arousability from sleep contributes to the increased risk of sudden death reported for sleep-deprived infants.

Thinking and hallucinating: Reciprocal changes in sleep

Internal deliberations (focused thoughts) and endogenous percepts (hallucinations) vary in a reciprocal manner across the states of waking and sleep, paralleling changes in regional brain activation. As subjects go from waking through sleep onset to NREM sleep and then to REM sleep, they report progressively more hallucinoid imagery and progressively less thinking. We have investigated whether this reciprocity in cognition between NREM and REM is maintained throughout the night. To do so, we analyzed 229 REM and 165 NREM reports collected with the Nightcap sleep monitoring system from 16 participants in their homes over 14 nights. The reports were scored for the presence of hallucinations and directed thinking by external judges. As predicted, hallucinations were more frequent in REM than in NREM for each segment of the night, and directed thinking was more frequent in NREM in the first 5 h of the night. Late in the night, directed thinking was equally infrequent in NREM and REM. At the same time, hallucinations increased within both NREM and REM as the night progressed, whereas directed thinking decreased in NREM and remained at a stable, low level in REM. These findings suggest that a reciprocal shift in focused thinking and hallucinating is a general property of cognitive activity across the wake-sleep cycle. Biological evidence supports the hypothesis that these cognitive changes are governed by specific state regulatory and neurocognitive processes at several levels of the brain.

REM sleep - by default?

Elements of three old, overlapping theories of REM sleep (REM) function, the Ontogenetic, Homeostatic and Phylogenetic hypotheses, together still provide a plausible framework - that REM (i) is directed towards early cortical development, (ii) "tones up" the sleeping cortex, (iii) can substitute for wakefulness, (iv) has a calming effect. This framework is developed in the light of recent findings. It is argued that the "primitiveness" of REM and its similarity to wakefulness liken it to a default state of "non-wakefulness" or a waking antagonist, anteceding "true" (non-REM) sleep. The "toning up" is reflected by inhibition of motor, sensory and (importantly) emotional systems, together pointing to integrated "flight or fight" activity, that preoccupies/distracts the organism when non-REM is absent and wakefulness unnecessary. Dreaming facilitates this distraction. In rodents, REM can provide stress coping and calming, but REM deprivation procedures incorporating immobility may further enhance stress and confound outcomes. REM "pressure" (e.g. REM rebounds) may be a default from a loss of inhibition of REM by non-REM. REM can be reduced and/or replaced by wakefulness, without adverse effects. REM has little advantage over wakefulness in providing positive cerebral recovery or memory consolidation.

Electrical stimulation of the amygdala increases the amplitude of elicited ponto-geniculo-occipital waves

The amygdala projects massively via its central nucleus (CNA) into brain stem regions involved in alerting and ponto-geniculo-occipital (PGO) wave generation. Electrical stimulation of CNA is known to enhance the acoustic startle response (ASR) and influence spontaneous PGO waves. The role of the amygdala in the modulation of ASR and elicited PGO waves (PGOE) was investigated in albino rats. Electrically stimulating CNA within 25 ms prior to an auditory stimulus enhanced ASR and PGOE amplitude in a similar way, with the largest response occurring when the electrical and auditory stimuli were given simultaneously. The data suggest that CNA modulates alerting mechanisms.

Localization of pontine PGO wave generation sites and their anatomical projections in the rat

A number of experimental and theoretical reports have suggested that the ponto-geniculo-occipital (PGO) wave-generating cells are involved in the generation of rapid eye movement (REM) sleep and REM sleep dependent cognitive functions. No studies to date have examined anatomical projections from PGO-generating cells to those brain structures involved in REM sleep generation and cognitive functions. In the present study, pontine PGO wave-generating sites were mapped by microinjecting carbachol in 74 sites of the rat brainstem. Those microinjections elicited PGO waves only when made in the dorsal part of the nucleus subcoeruleus of the pons. In six rats, the anterograde tracer biotinylated dextran amine (BDA) was microinjected into the physiologically identified cholinoceptive pontine PGO-generating site to identify brain structures receiving efferent projections from those PGO-generating sites. In all cases, small volume injections of BDA in the cholinoceptive pontine PGO-generating sites resulted in anterograde labeling of fibers and terminals in many regions of the brain. The most important output structures of those PGO-generating cells were the occipital cortex, entorhinal cortex, piriform cortex, amygdala, hippocampus, and many other thalamic, hypothalamic, and brainstem nuclei that participate in the generation of REM sleep. These findings provide anatomical evidence for the hypothesis that the PGO-generating cells in the pons could be involved in the generation of REM sleep. Since PGO-generating cells project to the entorhinal cortex, piriform cortex, amygdala, and hippocampus, these PGO-generating cells could also be involved in the modulation of cognitive functions.

Auditory arousal thresholds are higher when infants sleep in the prone position

OBJECTIVE

To evaluate the possibility that infants sleeping in the prone position have higher arousal thresholds to auditory challenges than when sleeping in the supine position.

STUDY DESIGN

Polygraphic recordings were performed for 1 night in 25 healthy infants with a median age of 9 weeks. The infants were exposed to white noises of increasing intensities while sleeping successively in the prone and supine positions, or vice versa. Arousal thresholds were defined by the auditory stimuli needed to induce polygraphic arousals.

RESULTS

Three infants were excluded from the study because they awoke while their position was being changed. For the 22 infants included in the analysis, more intense auditory stimuli were needed to arouse the infants in the prone position than those in the supine body position (p = 0.011). Arousal thresholds were higher in the prone than in the supine position in 15 infants; unchanged in 4 infants; and lower in the prone position in 3 infants (p = 0.007).

CONCLUSIONS

Infants show higher arousal thresholds to auditory challenges when sleeping in the prone position than when sleeping in the supine position. The finding could be relevant to mechanisms concerned with the reported association between sudden deaths and the prone sleeping position in infants.

Relationship between sensory stimuli-elicited IPSPs in motoneurons and PGO waves during cholinergically induced muscle atonia

Inhibitory postsynaptic potentials (IPSPs) can be produced in masseter motoneurons by sensory stimuli after the injection of carbachol into the nucleus pontis oralis (NPO) of alpha-chloralose-anesthetized cats. We have postulated previously that these IPSPs, which are induced in masseter motoneurons by sensory stimuli, arise as the result of phasic activation of the motor inhibitory system that mediates atonia occurring spontaneously during active sleep. In the present study, we determined that sensory stimuli, which excite different sensory pathways, somatosensory and auditory, also elicit ponto-geniculo-occipital (PGO) waves during the carbachol-induced state. Because the elicitation of PGO waves has been hypothesized to be a central sign of activation of alerting mechanisms, we suggest that these stimuli also excite those CNS structures that are involved in the alerting network. The temporal association of the sensory stimuli-elicited IPSPs and PGO waves also was examined by correlating the intracellular response of masseter motoneurons and the extracellular response of lateral geniculate nuclei neurons to somatosensory and auditory stimuli. Sensory stimuli produced an IPSP that had a similar latency from the foot of the elicited PGO wave as that of spontaneously occurring motoneuron IPSPs and PGO waves that occur during both carbachol-induced muscle atonia and naturally occurring active sleep. In addition, the intensity of the stimulus necessary for elicitation of PGO waves was found to be lower than that required for the elicitation of IPSPs in motoneurons. Additionally, evoked responses in masseter motoneurons during the carbachol-induced state were graded in response to increases in stimulus intensity. The preceding data suggest that some type of processing of sensory input occurs such that only those stimuli that are capable of activating alerting mechanisms involved in the generation of PGO waves result in an increase in activity in the motor inhibitory system. We conclude that there may be a functional link between alerting mechanisms involved in the generation of PGO waves and the motor inhibitory system that generates IPSPs in motoneurons. This functional link may serve to preserve atonia, and thus the state of active sleep, from potentially disruptive PGO-related influences that, during other behavioral states, result in motor activation.

Darkness facilitates the acoustic startle reflex in humans

The effects of darkness on startle reactivity and prepulse inhibition were investigated in two studies with 25 subjects participating in each study. Acoustic startle stimuli that were or were not preceded by an acoustic prepulse were delivered in alternating periods of complete darkness or light. In both studies, darkness significantly increased the magnitude of startle but did not affect prepulse inhibition (PPI). The PPI results suggest that darkness did not increase attention to the auditory modality, so that the startle facilitation in the dark probably did not result from an attentional process. The increased startle in the dark was significantly correlated with the intensity of subjects' fear of the dark as children based on retrospective rating scales. It is hypothesized that the startle facilitation in the dark results from a change in affect rather than from a change in attention.

Cellular basis of pontine ponto-geniculo-occipital wave generation and modulation

1. Pontogeniculooccipital (PGO) waves are recorded during rapid eye movement (REM) sleep from the pontine reticular formation. 2. PGO wave-like field potentials can also be recorded in many other parts of the brain in addition to the pontine reticular formation, but their distribution is different in different species. Species differences are due to variation in species-specific postsynaptic target sites of the pontine PGO generator. 3. The triggering neurons of the pontine PGO wave generator are located within the caudolateral peribrachial and the locus subceruleus areas. 4. The transferring neurons of the pontine PGO generator are located within the cholinergic neurons of the laterodorsal tegmentum and the pedunculopontine tegmentum. 5. The triggering and transferring neurons of the pontine PGO wave generator are modulated by aminergic, cholinergic, nitroxergic, GABA-ergic, and glycinergic cells of the brainstem. The PGO system is also modulated by suprachiasmatic, amygdaloid, vestibular, and brainstem auditory cell groups.

Suppression of ponto-geniculo-occipital waves by neurotoxic lesions of pontine caudo-lateral peribrachial cells

Ponto-geniculo-occipital waves precede rapid eye movement sleep and play an important role in triggering and maintaining rapid eye movement sleep. Ponto-geniculo-occipital waves have been implicated in several important functions such as sensorimotor integration, learning, cognition, development of the visual system, visual hallucination, and startle response. Peribrachial area neurons have long been thought to play a key role in the triggering of ponto-geniculo-occipital wave. However, the exact location within the peribrachial area for triggering pontine ponto-geniculo-occipital wave has not been unequivocally demonstrated. In an attempt to address this issue, kainic acid was microinjected (1.0 micrograms) unilaterally into the caudo-lateral peribrachial area of four cats in order to destroy the cell bodies located in that region and thus to study the effects of their destruction upon waking-sleep states and ponto-geniculo-occipital waves. The kainic acid produced a small spherical area of nerve cell loss and/or gliosis centered on the stereotaxic coordinates of P: 4.0, L: 4.5, and H: -2.5. The maximum diameter of that spherical area of cell loss was 0.9 mm. Unilateral lesioning of the caudo-lateral peribrachial area decreased ponto-geniculo-occipital waves during rapid eye movement sleep by 85% ipsi-laterally and 15% contralaterally in the lateral geniculate body without significantly changing the amounts of time spent in wake, slow-wave sleep, and rapid eye movement sleep. These results suggest that the caudo-lateral peribrachial area cells are critical to the genesis of ponto-geniculo-occipital waves, and provide compelling evidence that the different parts of the peribrachial area have quite different roles in the generation of discrete rapid eye movement sleep signs. We propose that caudo-lateral peribrachial cells exert an excitatory influence on rostral peribrachial cells, which then directly activate the ponto-geniculo-occipital waves that are recorded in the lateral geniculate body. Results of this study are not only important to understand the mechanisms generating ponto-geniculo-occipital waves but also could be used as an experimental tool to study the functions of this wave.

Sleep patterning and behaviour in cats with pontine lesions creating REM without atonia

Lesions of the dorsal pontine tegmentum release muscle tone and motor behaviour, much of it similar to orienting during wakefulness, into rapid eye movement sleep (REM), a state normally characterized by paralysis. Sleep after pontine lesions may be altered, with more REM-A episodes of shorter duration compared to normal REM. We examined behaviour, ponto-geniculo-occipital (PGO) waves (which may be central markers of orienting) and sleep in lesioned cats: (i) to characterize the relationship of PGO waves to behaviour in REM-A; (ii) to determine whether post-lesion changes in the timing and duration of REM-A episodes were due to activity-related awakenings: and (iii) to determine whether alterations in sleep changed the circadian sleep/wake cycle in cats. Behavioural release in REM-A was generally related to episode length, but episode length was not necessarily shorter than normal REM in cats capable of full locomotion in REM-A. PGO wave frequency was reduced overall during REM-A, but was higher during REM-A with behaviour than during quiet REM-A without overt behaviour. Pontine lesions did not significantly alter the circadian sleep/wake cycle: REM-A had approximately the same Light/Dark distribution as normal REM. Differences in the patterning of normal REM and REM-A within sleep involve more than mere movement-induced awakenings. Brainstem lesions that eliminate the atonia of REM may damage neural circuitry involved in REM initiation and maintenance; this circuitry is separate from circadian control mechanisms.

Rapid eye movement sleep disturbance in posttraumatic stress disorder

The subjective sleep disturbance in posttraumatic stress disorder (PTSD), including the repetitive, stereotypical anxiety dream, suggests dysfunctional rapid eye movement (REM) sleep mechanisms. The polysomnograms of a group of physically healthy combat veterans with current PTSD were compared with those of an age-appropriate normal control group. Tonic and phasic REM sleep measures in the PTSD subjects were elevated on the second night of recorded sleep. Increased phasic REM sleep activity persisted in the PTSD group on the subsequent night. During the study, an anxiety dream occurred in a PTSD subject in REM sleep. The results are consistent with the view that a dysregulation of the REM sleep control system, particularly phasic event generation, may be involved in the pathogenesis of PTSD. The finding of a specific disturbance of sleep unique to PTSD may have significant implications for the design of effective treatments for PTSD.

The amplitude of elicited PGO waves: a correlate of orienting

Ponto-geniculo-occipital (PGO) waves spontaneously occur in the pons, lateral geniculate body (LGB), and occipital cortex during rapid eye movement sleep (REM), and PGO-like waves (PGOE) may be elicited in LGB during sleep and waking. Because REM has been hypothesized to be a state of continual "orienting" or "hyper-alertness," we tested whether the amplitudes of PGOE in "alerting" situations (the abrupt onset of a loud sound or presentation of a novel stimulus within a series of stimuli) that evoke orienting responses (OR) would be greater than those following stimuli without OR. We also compared PGOE accompanying OR to PGOE during REM and NREM when OR are absent. The amplitudes of PGOE in W were greatest when OR were observed, and the amplitudes of PGOE accompanying OR were not significantly different from PGOE amplitudes in REM. Likewise, the amplitudes of PGOE during REM were not significantly different from those of the highest amplitude spontaneous PGO waves. We propose that the presence of PGOE signals registration of stimuli and that stimuli of sufficient significance to induce behavioral OR in waking also elicit PGOE of significantly greater amplitudes in all behavioral states. These findings support the hypothesis that the presence of high-amplitude PGO waves in REM indicates that the brain is in a state of more-or-less continual orienting.

Symposium: Dream research methodology: Mechanisms underlying oneiric behaviour released in REM sleep by pontine lesions in cats

Bilateral thermal lesions in the feline pontine tegmentum release elaborate behaviours during rapid eye movement sleep (REM). The behaviours, which are lesion-site specific, are consistent with the brain's paradoxical appearance of 'alertness' in REM and are largely isolated from environmental events, as are human dreams. This phenomenon may aid in understanding the neurophysiology underlying human dreams but offers little to the unravelling of their cognitive aspects.

Spontaneous phasic activity in the brain: differences between waves in lateral geniculate and central lateral nuclei across sleep states

Ponto-geniculo-occipital (PGO) waves are spontaneously-occurring macropotential waveforms recorded in the pons, lateral geniculate body (LGB) and occipital cortex. PGO waves mark the onset and course of rapid eye movement sleep (REM). PGO-like waves can be recorded in several brain areas including the thalamic central lateral nucleus (CL). Alerting stimuli elicit PGO waves (PGOE) from LGB and waves from CL (CLE) in all behavioural states. We compared spontaneous activity in LGB and CL across behavioral states to examine the relationship of CL waves to PGO waves. Spontaneous waves in LGB and CL may occur concurrently or separately in all states. Although REM is marked by a high level of LGB PGO activity, CL waves are rare. Frequencies of CL and LGB waves are similar in non-REM (NREM) although the waves do not necessarily occur at the same time. These findings suggest that the widespread phasic activity recorded throughout the brain in sleep cannot be assumed to be a non-specific unitary phenomenon propagated from a single brainstem generator.