Paradoxical sleep and the nature-nurture controversy

Continuity and change in neural plasticity through embryonic morphogenesis, fetal activity-dependent synaptogenesis, and infant memory consolidation

There is an apparent continuity in human neural development that can be traced to venerable themes of vertebrate morphogenesis that have shaped the evolution of the reptilian telencephalon (including both primitive three-layered cortex and basal ganglia) and then the subsequent evolution of the mammalian six-layered neocortex. In this theoretical analysis, we propose that an evolutionary-developmental analysis of these general morphogenetic themes can help to explain the embryonic development of the dual divisions of the limbic system that control the dorsal and ventral networks of the human neocortex. These include the archicortical (dorsal limbic) Papez circuits regulated by the hippocampus that organize spatial, contextual memory, as well as the paleocortical (ventral limbic) circuits that organize object memory. We review evidence that these dorsal and ventral limbic divisions are controlled by the differential actions of brainstem lemnothalamic and midbrain collothalamic arousal control systems, respectively, thereby traversing the vertebrate subcortical neuraxis. These dual control systems are first seen shaping the phyletic morphogenesis of the archicortical and paleocortical foundations of the forebrain in embryogenesis. They then provide dual modes of activity-dependent synaptic organization in the active (lemnothalamic) and quiet (collothalamic) stages of fetal sleep. Finally, these regulatory systems mature to form the major systems of memory consolidation of postnatal development, including the rapid eye movement (lemnothalamic) consolidation of implicit memory and social attachment in the first year, and then-in a subsequent stage-the non-REM (collothalamic) consolidation of explicit memory that is integral to the autonomy and individuation of the second year of life.

Neural bases of freedom and responsibility

This review presents a broad perspective of the Neuroscience of our days with special attention to how the brain generates our behaviors, emotions, and mental states. It describes in detail how unconscious and conscious processing of sensorimotor and mental information takes place in our brains. Likewise, classic and recent experiments illustrating the neuroscientific foundations regarding the behavioral and cognitive abilities of animals and, in particular, of human beings are described. Special attention is applied to the description of the different neural regulatory systems dealing with behavioral, cognitive, and emotional functions. Finally, the brain process for decision-making, and its relationship with individual free will and responsibility, are also described.

Neurophysiological Mechanisms of Implicit and Explicit Memory in the Process of Consciousness

Neurophysiological mechanisms are increasingly understood to constitute the foundations of human conscious experience. These include the capacity for ongoing memory, achieved through a hierarchy of reentrant cross-laminar connections across limbic, heteromodal, unimodal, and primary cortices. The neurophysiological mechanisms of consciousness also include the capacity for volitional direction of attention to the ongoing cognitive process, through a reentrant fronto-thalamo-cortical network regulation of the inhibitory thalamic reticular nucleus. More elusive is the way that discrete objects of subjective experience, such as the color of deep blue or the sound of middle C, could be generated by neural mechanisms. Explaining such ineffable qualities of subjective experience is what Chalmers has called “the hard problem of consciousness,” which has divided modern neuroscientists and philosophers alike. We propose that insight into the appearance of the hard problem can be gained through integrating classical phenomenological studies of experience with recent progress in the differential neurophysiology of consolidating explicit versus implicit memory. Although the achievement of consciousness, once it is reflected upon, becomes explicit, the underlying process of generating consciousness, through neurophysiological mechanisms, is largely implicit. Studying the neurophysiological mechanisms of adaptive implicit memory, including brain stem, limbic, and thalamic regulation of neocortical representations, may lead to a more extended phenomenological understanding of both the neurophysiological process and the subjective experience of consciousness.

NEW & NOTEWORTHY The process of consciousness, generating the qualia that may appear to be irreducible qualities of experience, can be understood to arise from neurophysiological mechanisms of memory. Implicit memory, organized by the lemnothalamic brain stem projections and dorsal limbic consolidation in REM sleep, supports the unconscious field and the quasi-conscious fringe of current awareness. Explicit memory, organized by the collothalamic midbrain projections and ventral limbic consolidation of NREM sleep, supports the focal objects of consciousness.

The subthalamic corticotropin-releasing hormone neurons mediate adaptive REM-sleep responses to threat

When an animal faces a threatening situation while asleep, rapid arousal is the essential prerequisite for an adequate response. Here, we find that predator stimuli induce immediate arousal from REM sleep compared with NREM sleep. Using in vivo neural activity recording and cell-type-specific manipulations, we identify neurons in the medial subthalamic nucleus (mSTN) expressing corticotropin-releasing hormone (CRH) that mediate arousal and defensive responses to acute predator threats received through multiple sensory modalities across REM sleep and wakefulness. We observe involvement of the same neurons in the normal regulation of REM sleep and the adaptive increase in REM sleep induced by sustained predator stress. Projections to the lateral globus pallidus (LGP) are the effector pathway for the threat-coping responses and REM-sleep expression. Together, our findings suggest adaptive REM-sleep responses could be protective against threats and uncover a critical component of the neural circuitry at their basis.

REM sleep stabilizes hypothalamic representation of feeding behavior

During rapid eye movement (REM) sleep, behavioral unresponsiveness contrasts strongly with intense brain-wide neural network dynamics. Yet, the physiological functions of this cellular activation remain unclear. Using in vivo calcium imaging in freely behaving mice, we found that inhibitory neurons in the lateral hypothalamus (LHvgat) show unique activity patterns during feeding that are reactivated during REM, but not non-REM, sleep. REM sleep-specific optogenetic silencing of LHvgat cells induced a reorganization of these activity patterns during subsequent feeding behaviors accompanied by decreased food intake. Our findings provide evidence for a role for REM sleep in the maintenance of cellular representations of feeding behavior.

Neonatal sleep, a genetically-driven rehearsal before the show: an endless encounter with Michel Jouvet

In this short review, I would like to share some personal memories about the insights and achievements of Michel Jouvet in the field of sleep ontogeny. The first time I met Michel Jouvet was in 1972 when he accepted to chair my thesis on sleep, the research work being preformed in Howard Roffwarg's lab in New York. From then on we had many discussions together about the mechanisms and nature of neonatal Paradoxical Sleep, notably its characteristic muscular "twitches". The idea emerged of a genetically programmed pattern of motor activation responsible for this state of "seismic" sleep. Such a pattern would underlie, for example, the facial mimics displayed during sleep in early life, whose function would be to "pre-practice" a specific behavior. Later on, in the 1980's Michel Jouvet had the masterful insight to extend this role of Paradoxical Sleep to the theory of genetic programming for maintaining psychological individualism. Michel Jouvet's scientific curiosity and generosity led to his exceptional accomplishments, and he will remain as an immense figure in the culture of sleep science.

Neurofeedback and the Neural Representation of Self: Lessons From Awake State and Sleep

Neurofeedback has been around for half a century, but despite some promising results it is not yet widely appreciated. Recently, some of the concerns about neurofeedback have been addressed with functional magnetic resonance imaging and magnetoencephalography adding their contributions to the long history of neurofeedback with electroencephalography. Attempts to address other concerns related to methodological issues with new experiments and meta-analysis of earlier studies, have opened up new questions about its efficacy. A key concern about neurofeedback is the missing framework to explain how improvements in very different and apparently unrelated conditions are achieved. Recent advances in neuroscience begin to address this concern. A particularly promising approach is the analysis of resting state of fMRI data, which has revealed robust covariations in brain networks that maintain their integrity in sleep and even anesthesia. Aberrant activity in three brain wide networks (i.e., the default mode, central executive and salience networks) has been associated with a number of psychiatric disorders. Recent publications have also suggested that neurofeedback guides the restoration of “normal” activity in these three networks. Using very recent results from our analysis of whole night MEG sleep data together with key concepts from developmental psychology, cloaked in modern neuroscience terms, a theoretical framework is proposed for a neural representation of the self, located at the core of a double onion-like structure of the default mode network. This framework fits a number of old and recent neuroscientific findings, and unites the way attention and memory operate in awake state and during sleep. In the process, safeguards are uncovered, put in place by evolution, before any interference with the core representation of self can proceed. Within this framework, neurofeedback is seen as set of methods for restoration of aberrant activity in large scale networks. The framework also admits quantitative measures of improvements to be made by personalized neurofeedback protocols. Finally, viewed through the framework developed, neurofeedback’s safe nature is revealed while raising some concerns for interventions that attempt to alter the neural self-representation bypassing the safeguards evolution has put in place.

REM sleep selectively prunes and maintains new synapses in development and learning

The functions and underlying mechanisms of rapid eye movement (REM) sleep remain unclear. Here we show that REM sleep prunes newly formed postsynaptic dendritic spines of layer 5 pyramidal neurons in the mouse motor cortex during development and motor learning. This REM sleep-dependent elimination of new spines facilitates subsequent spine formation during development and when a new motor task is learned, indicating a role for REM sleep in pruning to balance the number of new spines formed over time. Moreover, REM sleep also strengthens and maintains newly formed spines, which are critical for neuronal circuit development and behavioral improvement after learning. We further show that dendritic calcium spikes arising during REM sleep are important for pruning and strengthening new spines. Together, these findings indicate that REM sleep has multifaceted functions in brain development, learning and memory consolidation by selectively eliminating and maintaining newly formed synapses via dendritic calcium spike-dependent mechanisms.

Mammalian sleep may have no adaptive advantage over simple activity-rest cycles

The adaptive value of sleep remains unknown in spite of the intense research performed throughout the last decades. However, few sleep researchers are aware of the difficulties posed by the blind acceptance of an extreme adaptationist viewpoint. Under this philosophy, every anatomical and functional detail present in a living being should have a positive adaptive value, a position that has been considered as rather doubtful. In this report, it is proposed that most of the physiological changes used for mammalian sleep definition could be mere by-products of other true adaptations, such as the ontogenetic and phylogenetic development of the nervous system. As a result, complex mammalian sleep could have no adaptive value over that of the simplest forms of rest-activity cycles present in all living forms. In addition, it is proposed that the absence of adaptive value should, by default, be the first option regarding the function of sleep. Besides, the burden of the proof should be always charged over the proponents of every particular adaptive function. As this proof has not been reached, it is the absence of function for sleep which should be taken for granted.

Hipnic modulation of cerebellar information processing: implications for the cerebro-cerebellar dialogue

Recent evidence indicates that during the sleep-waking cycle the forebrain and the cerebellum show parallel changes of their operating capabilities and suggest that cooperation between these two structures plays a different role in the different behavioral states. In particular, a high degree of cerebro-cerebellar cooperation is expected in waking and in paradoxical sleep when enhanced information processing within the cerebellum and the cortex is associated with effective reciprocal cerebro-cerebellar signal transmission. We first speculate that during waking, a state in which a wide range of behaviors is produced by the interaction with the external world, the cerebellum might assist the cortex to develop the neural dynamic patterns which underlie behaviors and that this could be accomplished via cerebellar modulation of both short- and long-range cortical synchronization. In particular, we propose that the cerebellum might favour the automatic triggering of the patterns already acquired, when requested by the context, as well as the acquisition of novel patterns, when found to be of adaptive value, and might even modulate the access to consciousness of brain operations, if producing unpredicted results, by regulating pattern complexity. This proposal is based on the experimental evidence that oscillatory activity may flow within the cerebro-cerebellar loops and that stimulation or lesion of the cerebellar structures affects cortical synchronization. Then we report evidence indicating that during paradoxical sleep, when brain activation occurs in the absence of sensory inflow and motor output, cerebro-cerebellar cooperation mainly favours consolidation of newly acquired waking patterns and/or savings of old patterns from disruption possibly through a non-utilitarian replay process. Finally, we propose that cerebro-cerebellar cooperation weakens during slow wave sleep, given that in this sleep state neuronal activity and excitability decrease both in the cerebellum and in the forebrain and cerebello-cortical signal transmission is at least partially gated at the thalamic level.

Postnatal development of rat hippocampal gamma rhythm in vivo

Network oscillations in the gamma-frequency band (20-100 Hz) may have a central role in the timing and coordination of neural activity in the adult brain, yet their appearance in the course of development has remained unexplored. Moreover, electroencephalogram (EEG)-based classification of the vigilance states [active sleep (AS), quiet sleep (QS), or awake (W)] has been thought to be possible only after the second postnatal week. We now report the presence of spontaneous hippocampal gamma oscillations in the area CA3 of freely moving rats at postnatal days (P) 5-10. Initially, at P5, the gamma oscillations were seen in time-frequency analyses of intrahippocampal EEG recordings as brief (<500 ms) bursts at 20-30 Hz. The early gamma rhythmicity was most pronounced during periods of AS but was occasionally detected also during QS. Toward P10, the gamma oscillations gained amplitude and extended also to higher (<or=60 Hz) frequencies. In parallel, the gamma oscillations were progressively more and more confined to AS. To further consolidate these findings, we compared amplitude spectra averaged within the behavioral categories. AS was characterized by the appearances of gamma (20-30 Hz) and theta (3-5 Hz) peaks at P6 and at P8, respectively. QS, on the other hand, had considerably smoother amplitude distributions between 1 and 100 Hz for P5-P10, with no peaks in gamma or theta bands. Hippocampal gamma rhythm thus seems to hallmark early AS. Our data provide the first in vivo evidence for both the presence and the behavioral correlate of spontaneous gamma oscillations in the newborn rat.

Alterations in respiratory behavior, brain neurochemistry and receptor density induced by pharmacologic suppression of sleep in the neonatal period

The present study examined if drug suppression of active sleep (AS) in the neonate affected the development and expression of respiratory behavior. Secondly, we assessed brain neurochemistry and receptor density in specific supra-medullary brain regions to identify coincident biochemical alterations. Sprague-Dawley newborn rat pups were randomized and divided among six rat mothers (n=10/mother/group), each mother housed separately. Two untreated control (UC) groups received either no interventions or were fed milk vehicle twice daily and were handled similarly to the drug intervention animals. Pharmacological disruption of sleep was achieved by administration (2 groups of each) of either clonidine (CLO) 100 microm/kg, or scopolamine (SCO) 800 microm/kg, given orally twice daily for the first 7 days of life. On postnatal (P) days P10 and P19 of life, pups were assessed for metabolism, minute ventilation (VE), tidal volume (Vt) and frequency (f). On P21 (14 days after the end of drug exposure), pups from each condition were sacrificed and punch biopsies of the frontal cortex, hypothalamus, and hippocampus were examined for hydroxytryptophan (5-HT), and norepinepherine (NE) by HPLC. An equal number of pups were sacrificed and brains examined for muscarinic acetylcholine (mAch), alpha2-adrenergic and I1-imidazoline receptor density.

RESULTS

Both CLO and SCO exposed animals had a lower V(t) and respiratory quotient than UC animals (p<0.01). CLO animals exhibited a higher f (p<0.01) and both CLO and SCO exhibited a lower V(t) (p<0.05) than the UC groups; VE was reduced in the SCO groups, compared with CLO and UC groups (p<0.01). Pattern of breathing in response to brief hypoxia exposure was altered for CLO and SCO. The normal decline in VE during sleep was not observed in CLO rats. Both drug exposures resulted in a comparable reduction in hypothalamic NE and 5-HT levels (p<0.05), while in the frontal cortex, and the hippocampus variable changes in NE and 5-HT, occurred. In CLO and SCO rats mAch receptors were increased in cortex, and reduced in hypothalamus; I1-imidazoline receptors were increased in hypothalamus and decreased in hippocampus (p<0.05 for each). In contrast, alpha2-adrenergic receptors were increased in cortex for both CLO and SCO, decreased in hypothalamus for CLO, and decreased in hippocampus for SCO (p<0.05 for each).

CONCLUSIONS

these data show that drug-induced neonatal sleep suppression will alter ventilatory pattern, metabolism, and site-specific concentrations of adrenergic neurotransmitters and in receptor density, perhaps as a result of suppression of neonatal AS.

Prenatal exposure to alcohol in adult rats: relationships between sleep and memory deficits, and effects of glucose administration on memory

Previous studies show that prenatal exposure to alcohol results in sleep deficits in rats, including reductions in paradoxical sleep. Little is known, however, about the extent or duration of sleep impairments beyond the neonatal period. The present experiment examined effects of prenatal exposure on sleep in young adulthood. Three-hour, daytime sleep EEGs were obtained in 6-month-old female rats prenatally exposed to alcohol. Compared to isocaloric pair-fed and ad libitum control groups, the alcohol-exposed group showed reduced paradoxical sleep. Non-paradoxical sleep did not differ between groups. Concurrent deficits were obtained in radial arm maze, but not inhibitory (passive) avoidance, performance. One year later, at the age of 18 months, alcohol-exposed rats showed deficits in spontaneous alternation behavior which were reversed by administration of glucose (100 mg/kg). Deficits in paradoxical sleep at 6 months of age were highly correlated with deficits in spontaneous alternation behavior at 18 months of age, in individual, alcohol-exposed animals. These results provide the first evidence that prenatal exposure to alcohol results in selective and persistent deficits in sleep. They also show that measures of paradoxical sleep can predict impaired memory over a large portion of the life span, and suggest that glucose can attenuate memory deficits in this population.

The function of fetal/neonatal rapid eye movement sleep

The hypothesis is put forward that rapid eye movement (REM) sleep in early life serves as (1) an indicator for the degree of brain maturation and (2) the promoter of further brain development. This hypothesis, although not exclusive, differs (a) from the theory of Roffwarg et al. that REM sleep substitutes for 'wakefulness' during the period (early life) in which wakefulness is limited, (b) from the theory of Crick and Mitchson, i.e., the 'unlearning' hypothesis of REM sleep, (c) from the theory of Jouvet, i.e., that REM sleep is a time for genetic read-out and (d) from the theory of Freud, i.e., that dreams fulfil our wishes (in other words, activation of neuronal systems that were disproportionally activated during wakefulness).

Strain difference in early postnatal sleep-wake behaviour between Alko Alcohol and Wistar rats

Early postnatal sleep-wake behaviour of male and female rats of Alko Alcohol and Wistar strain was studied using a static charge sensitive mattress when the rats were aged 1 and 2 weeks postnatally. In both strains and sexes, waking time relative to total recording time increased, proportion of quiet state did not change, and that of active sleep decreased during the second postnatal week. The number of long active sleep stages relative to short active sleep stages and the duration of sleep-wake stages increased with age. Transitions between quiet state and active sleep became fewer with increasing age. Waking time increased more in Wistar rats than in Alko Alcohol rats. At 1-2 weeks of age, the percentage of active sleep and the number of long active sleep stages relative to short active sleep stages were larger, and the duration of sleep-wake stages longer in Alko Alcohol than in Wistar rats. Sleep-wake behaviour did not differ between the sexes of either strain or age. Selective breeding for high alcohol preference in Alko Alcohol rats may have caused a genetic trait in early postnatal sleep-wake behaviour.

The maturational theory of brain development and cerebral excitability in the multifactorially inherited manic-depressive psychosis and schizophrenia

An association has been established between the multifactorially inherited rate of physical maturation and the final step in brain development, when some 40% of synapses are eliminated. This may imply that similarly to endocrine disease entities, we have cerebral disease entities at the extremes of the maturational rate continuum. The restriction of prepubertal pruning to excitatory synapses leaving the number of inhibitory ones fairly constant, implies changes in cerebral excitability as a function of rate of maturation (age at puberty). In early maturation there will be an excess in excitatory drive due to prematurely abridged pruning, which compounds a synchronization tendency inherent in excessive synaptic density. Lowering excitatory level with antiepileptics is hypothesized to be a logical treatment in this type of brain dysfunction. In late maturation, a deficit in excitatory drive due to failure to shut down the pruning process associated with a tendency to the breakdown of circuitry and desynchronization, adds to a similar adversity inherent in reduced synaptic density. Raising the excitatory level with convulsants is hypothesized to be the treatment for this type of CNS dysfunction. The maturational theory of Kraepelin's psychoses holds that they are naturally occurring contrasting chemical signaling disorders in the brain at the extremes of the maturational rate continuum: manic depressive psychosis is a disorder of the early maturer and comprises raised cerebral excitability and a raised density of synapses. This is successfully treated with anti-epileptics like sodium valproate and carbamazepin. Schizophrenia is a disorder in late maturation with reduced cerebral excitability and reduced synaptic density. This is accordingly treated with convulsants such as typical and atypical neuroleptics. However, the conventional effective treatments in both disorders act on inhibition only by either lowering or raising inhibitory level. While the neuroleptics drugs are superior anti-psychotics they nevertheless do not affect the deviation in cerebral excitability which would explain why they do not cure. Disturbed circadian rhythms which precede psychotic episodes in manic depressives accord with a primary dysfunction in the CNS, the suprachiasmatic nucleus of the hypothalamus via its direct input the glutamatergic retinohypothalamic tract. The residual deficits in schizophrenia accord with persistently disconnected circuitry and communication which is a consequence of reduced excitatory level and is manifested in insufficient motivation, a reduced drive associated hypofunction, and neuromuscular dysfunction.

Sleep deficits in rats after NMDA receptor blockade

N-Methyl-D-aspartate (NMDA) receptor blockade disrupts a variety of functions associated with neural plasticity, including acquisition of learned responses and long-term potentiation. Deficits in memory are significantly correlated with deficits in measures of paradoxical sleep in several amnesic populations. The present experiment therefore assessed whether NPC 12626, a competitive NMDA receptor antagonist, also disrupts sleep. NPC 12626 (1, 10, 50, and 100 mg/kg) or saline was administered to Sprague-Dawley rats 30 min prior to 3-h daytime recording periods. Paradoxical sleep was selectively impaired at all but the highest dose, which prevented all sleep during the recording period. Some deficits in nonparadoxical sleep first appeared at the 10 mg/kg dose but did not became prominent until the 50 mg/kg dose. The results thus show that NPC 12626 impairs sleep states in rats and demonstrate that paradoxical sleep is particularly susceptible to the effects of NMDA receptor blockade. These findings, along with previous evidence that NMDA antagonists impair waking measures of arousal, provide evidence that all sleep-wake states are impaired by NMDA receptor blockade. More generally, the results suggest that some brain mechanisms underlying sleep and memory may share common elements.

A function for REM sleep: regulation of noradrenergic receptor sensitivity

We hypothesize that REM sleep serves to upregulate and/or prevent downregulation of brain norepinephrine (NE) receptors. This hypothesis is based on the following observations: (1) NE neurons of the locus coeruleus (LC) are tonically active in waking and non-REM sleep, but the entire population of LC NE neurons is inactive during REM sleep. (2) Continuous presence of NE or adrenoceptor agonists downregulates NE receptors, while a reduction in NE availability upregulates these receptors. (3) The effects of REM sleep deprivation are similar to those of NE receptor downregulation. Recent biochemical studies of NE receptor sensitivity provide strong experimental support for this hypothesis. The functional consequence of enhanced NE receptor 'tone' brought about by REM sleep would be improved signal processing in diverse brain systems, thus endowing the organism with a selective advantage. This hypothesis makes a number of specific predictions which can be tested with currently available techniques, and suggests new ways of understanding the evolution and postnatal development of REM sleep.

Circadian oscillations of DNA synthesis in rat brain

The possibility that the synthesis of brain DNA undergoes a circadian fluctuation was examined in male adult Wistar rats, kept under natural lighting conditions or born and raised under artificial lighting conditions. Groups of rats were taken every 4 h during the 24 h, injected subcutaneously with [methyl-3H]thymidine and killed 4 h later. By cosinor analysis, the DNA specific activity of cerebral hemispheres and brainstem was found to show a significant 24 h rhythm with the peak at the beginning of the dark period (waking period). By contrast, in kidney, the peak of the circadian rhythm of DNA specific activity occurred during the light period (sleep period), in agreement with literature data. On the other hand, in 4-week-old rats, born and raised in artificial lighting conditions, brain DNA specific activity followed a 12 h rhythm, in agreement with the lack of a significant diurnal oscillation of the sleep--waking structure. It is concluded that brain DNA synthesis undergoes a circadian fluctuation in association with the circadian rhythm of waking.

Effect of neonatal nomifensine exposure on adult behavior and brain monoamines in rats

The aim of the study was to examine the effects of early postnatal exposure to nomifensine, an inhibitor of catecholamine uptake, on concurrent active (REM) sleep, on later alcohol related behavior and on monoamine concentrations in various brain regions of rats. For these purposes rats were given daily injections of 10 mg/kg nomifensine s.c. between the 7th and the 18th postnatal days. During the nomifensine exposure active sleep, expressed as a percentage of total sleeping time, was reduced. At one month of age, the nomifensine rats showed increased ambulation and had lower defecation scores in the open-field than the controls. Neonatal exposure to nomifensine increased voluntary intake of 10% (v/v) alcohol when the rats were 2-3 months of age. The rats, however, did not exhibit preservation in the T-maze, and similarly to control rats suppressed drinking 0.1 M lithium chloride even when thirsty. Measurement of cerebral monoamine concentrations at the age of 3 months suggested that neonatal nomifensine treatment interferes with the noradrenergic and serotonergic systems in several regions of the brain. Concentrations of noradrenaline and 5-hydroxyindoleacetic acid (5-HIAA) were decreased in the cerebral cortex and frontal cortex, concentration of 5-HIAA was decreased in the neostriatum, and concentrations of noradrenaline, 5-hydroxytryptamine (5-HT) and 5-HIAA were elevated in the lower brain stem. Taken together, these findings show that exposure to nomifensine during the 2nd and 3rd postnatal weeks suppresses neonatal active sleep, causes changes in the adult open-field behavior, and increases voluntary alcohol intake, perhaps due to a long-lasting alteration in brain monoamines.

Effect of sleep on cerebral DNA synthesized during shuttle-box avoidance training

Female Wistar rats weighing 200 g were implanted with cortical electrodes and two intraventricular cannulae. Five days later they were given 3H-thymidine and exposed to shuttle-box training for four hours. They were then left free to sleep in the following three hours during which their EEG activity was recorded. In comparison with control animals (C), learning (L) and non-learning (NL) rats exhibited an increase in SS. In comparison to the EEG recording made the previous day, all animal groups displayed an increase in SS, but only NL rats suffered a decrease in PS(%). The specific radioactivity of DNA measured in several brain regions was tendentially lower in NL rats, but significance was achieved only in the cerebellum in the comparison between NL rats and C rats. No change occurred in liver. More marked and significant decrements in the DNA specific radioactivity of all brain regions were observed in the subgroup of NL rats displaying relatively high values of PS time in comparison to the analogous subgroups of C and L animals. Comparable decrements were present with regard to the subgroup of NL rats endowed with relatively low PS time. Less widespread and more limited changes were observed in the concentration of acid-soluble radioactivity. In addition, several significant correlations were detected by Spearman's analysis among behavioral, biochemical and sleep parameters. The results are consistent with the interpretation that the selective decrease in brain radioactive DNA observed in NL rats reflects a loss of DNA synthesized during the training period. The loss is related to the amount of post-training PS and is associated to a lengthening of the mean duration of PS episodes. It may be concluded that the loss of newly-synthesized brain DNA reflects the elimination of molecules associated with neural information devoid of adaptive value.

The consolidation hypothesis for REM sleep function: stress and other confounding factors--a review

One commonly held hypothesis about the function of REM sleep (RS) concerns the consolidation of plastic processes, particularly those relating to learning and memory. The majority of the experimental data apparently supporting this hypothesis come from RS deprivation (RSD) studies. However, this review points out that: (i) there are several shortcomings with the methodology of animal RSD investigations, (ii) RSD seems to produce arousal and stereotyped behaviour which may interfere with learning etc., and consequently give artificial support to the hypothesis. The review then examines evidence outside the field of RSD, relating to the hypothesis, which seems further to confound or contradict it. Whilst the hypothesis is not rejected, these problems need to be addressed further by its supporters.

The function of dream sleep

We propose that the function of dream sleep (more properly rapid-eye movement or REM sleep) is to remove certain undesirable modes of interaction in networks of cells in the cerebral cortex. We postulate that this is done in REM sleep by a reverse learning mechanism (see also p. 158), so that the trace in the brain of the unconscious dream is weakened, rather than strengthened, by the dream.