Neuronal excitability control in health and disease: a neurophysiological comparison of REM sleep and epilepsy

Minds and Brains, Sleep and Psychiatry

Objective

This article offers a philosophical thesis for psychiatric disorders that rests upon some simple truths about the mind and brain. Specifically, it asks whether the dual aspect monism—that emerges from sleep research and theoretical neurobiology—can be applied to pathophysiology and psychopathology in psychiatry.

Methods

Our starting point is that the mind and brain are emergent aspects of the same (neuronal) dynamics; namely, the brain–mind. Our endpoint is that synaptic dysconnection syndromes inherit the same dual aspect; namely, aberrant inference or belief updating on the one hand, and a failure of neuromodulatory synaptic gain control on the other. We start with some basic considerations from sleep research that integrate the phenomenology of dreaming with the neurophysiology of sleep.

Results

We then leverage this treatment by treating the brain as an organ of inference. Our particular focus is on the role of precision (i.e., the representation of uncertainty) in belief updating and the accompanying synaptic mechanisms.

Conclusions

Finally, we suggest a dual aspect approach—based upon belief updating (i.e., mind processes) and its neurophysiological implementation (i.e., brain processes)—has a wide explanatory compass for psychiatry and various movement disorders. This approach identifies the kind of pathophysiology that underwrites psychopathology—and points to certain psychotherapeutic and psychopharmacological targets, which may stand in mechanistic relation to each other.

The ‘mind’ emerges from Bayesian belief updating in the ‘brain’

Psychopathology can be read as aberrant belief updating.

Aberrant belief updating follows from any neuromodulatory synaptopathy

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.

Dissociative states in dreams and brain chaos: implications for creative awareness

This article reviews recent findings indicating some common brain processes during dissociative states and dreaming with the aim to outline a perspective that neural chaotic states during dreaming can be closely related to dissociative states that may manifest in dreams scenery. These data are in agreement with various clinical findings that dissociated states can be projected into the "dream scenery" in REM sleep periods and dreams may represent their specific interactions that may uncover unusual psychological potential of creativity in psychotherapy, art, and scientific discoveries.

Evolving concepts of sleep cycle generation: From brain centers to neuronal populations

As neurophysiological investigations of sleep cycle control have provided an increasingly detailed picture of events at the cellular level, the concept that the sleep cycle is generated by the interaction of multiple, anatomically distributed sets of neurons has gradually replaced the hypothesis that sleep is generated by a single, highly localized neuronal oscillator.

Cell groups that discharge during rapid-eye-movement (REM) sleep (REM-on) and neurons that slow or cease firing during REM sleep (REM-off) have long been thought to comprise at least two neurochemically distinct populations. The fact that putatively cholinoceptive and/or cholinergic (REM-on) and putatively aminergic (REM-off) cell populations discharge reciprocally over the sleep cycle suggests a causal interdependence.

In some brain stem areas these cell groups are not anatomically segregated and may instead be neurochemically mixed (interpenetrated). This finding raises important theoretical and practical issues not anticipated in the original reciprocal-interaction model. The electrophysiological evidence concerning the REM-on and REM-off cell groups suggests a gradient of sleep-dependent membrane excitability changes that may be a function of the connectivity strength within an anatomically distributed neuronal network. The connectivity strength may be influenced by the degree of neurochemical interpenetration between the REM-on and REM-offcells. Recognition of these complexities forces us to revise the reciprocal-interaction model and to seek new methods to test its tenets.

Cholinergic microinjection experiments indicate that some populations of REM-on cells can execute specific portions of the REM sleep syndrome or block the generation of REM sleep. This observation suggests that the order of activation within the anatomically distributed generator populations may be critical in determining behavioral outcome. Support for the cholinergic tenets of the reciprocal-interaction model has been reinforced by observations from sleep-disorders medicine.

Specific predictions of the reciprocal-interaction model and suggestions for testing these predictions are enumerated for future experimental programs that aim to understand the cellular and molecular basis of the mammalian sleep cycle.

Temporal binding at gamma frequencies in the brain: paving the way to epilepsy?

Fast (beta-gamma band 20-100 Hz) rhythms of electrical activity of the brain have been suggested to play an important role in perception, cognition and consciousness providing temporal binding of neural activities and allowing the formation of mental representations. The recent advances in the concept of temporal binding and their relation to the theory of neural networks (connectionism) are reviewed here as well as some experimental results concerning the intensified gamma rhythms and epilepsy. The hippocampal-neocortical gamma rhythms are extremely intense and hypersynchronous at onset of the epileptiform discharges induced by systemic kainic acid in the rat. Those gamma rhythms are followed by a slow rhythm of epileptiform spikes/sharp waves or spike-wave complexes ('spike-wave' activity). During spike-wave activity, gamma synchronisation is significantly decreased. A novel unifying concept is proposed which relates the associative principle of neural networks to the mechanism of temporal binding at high frequencies. It suggests that for each memory stored in an associative network there is a corresponding quasi-stable state of synchronous oscillation at some frequency within the gamma band. It also suggests that excessive temporal binding ("over-binding") occurs at seizure onset when abnormally intensified and globally synchronous fast activity is often observed. "Over-binding" may cause the undesirable formation of false associations due to inadequate synaptic modifications. To prevent this process, spike-wave discharge develops as an extreme activation of the mechanism capable to desynchronise and eventually suppress fast activity and erase the spurious modes of activity associated with hypersynchronous gamma rhythms. Thus, spike-wave activity is suggested to be the "anti-binding" mechanism. This mechanism is also related to the spikes/sharp waves normally occurring in the brain mostly in sleep. It is qualitatively similar to the "unlearning" mechanism of Crick and Mitchison presumably associated with the PGO spikes of the REM sleep.

Possible involvement of an endogenous benzodiazepine receptor ligand of the inverse agonist type in the regulation of rapid-eye movement (REM) sleep: an hypothesis

1. Rapid-eye movement (REM) sleep is a complex behavioral state characterized by desynchronized electroencephalographic (EEG) activity, postural atonia, rapid, saccadic movements of the eyes, and vivid dreaming. 2. A recently developed class of drugs, the inverse agonist beta-carboline-3-carboxylates, elicits a number of effects similar to the properties of REM sleep, such as desynchronized cortical EEG and penile erections. 3. The hypothesis is put forth that an endogenous beta-carboline-3-carboxylate exists which may initiate many aspects of REM sleep. 4. Clinical relevance of this hypothesis is discussed with regard to REM anxiety dreams, night terrors, narcolepsy, and depression.

Pro- and anticonvulsant effects of stress: the role of neuroactive steroids

The present review deals with findings related to the contribution of pro- and anticonvulsant effects of "neuroactive" steroids and the role of the gamma-aminobutyric acid (GABA) receptor as a physiological target for naturally occurring steroids. Ways are discussed via which GABAergic neurotransmission can be enhanced or reduced following maneuvers that inflict stress. The duality of stress effects is emphasized in conjunction with different types of epileptogenesis (e.g., grand mal vs petit mal) that undergo dissimilar evolution. Among the issues covered are steroid-induced sedation and epileptogenicity, excitatory steroids, stress and epilepsy, GABA and respiratory functions, asymmetric brain injury, and psychopathology and stress.

Mechanisms of seizure suppression during rapid-eye-movement (REM) sleep in cats

REM sleep is the most antiepileptic state in the sleep-wake cycle for human generalized epilepsy, yet the neural mechanism is unknown. This study verified the antiepileptic properties of REM sleep in feline generalized epilepsy and also isolated the responsible factors. Conclusions are based on 20 cats evaluated for generalized EEG and motor seizure susceptibility before and after dissociation of specific REM sleep components. Bilateral electrolytic lesions of the medial-lateral pontine tegmentum created a syndrome of REM sleep without atonia. Systemic atropine created a syndrome of REM sleep without thalamocortical EEG desynchronization. Identical results were obtained in two seizure models, systemic penicillin epilepsy and electroconvulsive shock. (1) Normal REM sleep retarded the spread of EEG seizure discharges and had even more potent anticonvulsant effects. (2) Selective loss of 'sleep paralysis' (skeletal muscle atonia) during REM abolished REM sleep protection against myoclonus and convulsions without affecting generalized EEG paroxysms. (3) Conversely, selective loss of thalamocortical EEG desychronization abolished REM sleep protection against generalized EEG seizures without affecting clinical motor accompaniment. These results suggest that the descending brainstem pathways which mediate lower motor neuron inhibition also protect against generalized motor seizures during REM sleep. Protection against spread of EEG paroxysms is governed by a separate mechanism, presumably the ascending brainstem pathways mediating intense thalamocortical EEG desynchronization during REM sleep.

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.

Brainstem experimental seizures produced by microinjections of carbachol

Microinjections of 2-10 micrograms of carbachol into the mesencephalic reticular formation (MRF) and pontine reticular formation (PRF) of rats consistently induced local electroencephalographic seizures. These seizures had organized, rhythmical patterns and were long lasting. They spread powerfully and bilaterally between the MRF and PRF and also to the hippocampus and cortex. The electroencephalographic seizures were accompanied by severe, long-lasting convulsions. These convulsions were clonic and bilateral, started in the head area and progressed rostro-caudally to become generalized to the entire body. Other nonconvulsive behaviors were activated by the seizures. Immobility and catalepsy were the most frequent nonconvulsive correlates of the brainstem carbachol seizures.

Pontogeniculooccipital waves: spontaneous visual system activity during rapid eye movement sleep

1. Pontogeniculooccipital (PGO) waves are recorded during rapid eye movement (REM) sleep from the pontine reticular formation, lateral geniculate bodies, and occipital cortex of many species. 2. PGO waves are associated with increased visual system excitability but arise spontaneously and not via stimulation of the primary visual afferents. Both auditory and somatosensory stimuli influence PGO wave activity. 3. Studies using a variety of techniques suggest that the pontine brain stem is the site of PGO wave generation. Immediately prior to the appearance of PGO waves, neurons located in the region of the brachium conjunctivum exhibit bursts of increased firing, while neurons in the dorsal raphe nuclei show a cessation of firing. 4. The administration of pharmacological agents antagonizing noradrenergic or serotonergic neurotransmission increases the occurrence of PGO waves independent of REM sleep. Cholinomimetic administration increases the occurrence of both PGO waves and other components of REM sleep. 5. Regarding function, the PGO wave-generating network has been postulated to inform the visual system about eye movements, to promote brain development, and to facilitate the response to novel environmental stimuli.