We propose that a theory of sleep involving the division of labor between two states of sleep–REM and non-REM, the latter of which has an abundance of ripple electrical activity–might allow for a fusion of the two main sleep theories. In particular, while REM sleep may contribute to the homeostatic weakening of overactive synapses, a prominent and transient oscillatory rhythm called “sharp-wave ripple” seems to allow for consolidation of behaviorally relevant memories across many structures of the brain. In this review, we will summarize these theories, but also focus on substantial new information regarding the relation of electrical brain rhythms to sleep. Existing data point most strongly to its role in memory and homeostasis: that sleep helps maintain basic brain functioning via a homeostatic mechanism that loosens connections between overworked synapses, and that sleep helps consolidate and re-form important memories. Steriade M, Datta S, Pare D, Oakson G, Curro Dossi R (1990) Neuronal activities in brainstem cholinergic nuclei related to tonic activation processes in thalamocortical systems.Sleep occupies roughly one-third of our lives, yet the scientific community is still not entirely clear on its purpose or function. Shosaku A, Kayama Y, Sumitomo I, Sugitani M, Iwama K (1989) Analysis of recurrent inhibitory circuit in rat thalamus: Neurophysiology of the thalamic reticular nucleus. Electroencephalogr Clin Neurophysiol 1: 155–173 Moruzzi G, Magoun HW (1949) Brain stem reticular formation and activation of the EEG. Koyama Y, Jodo E, Kayama Y (1994) Sensory responsiveness of “broad-spike” neurons in the laterodorsal tegmental nucleus, locus coeruleus and dorsal raphe of awake rats: Implications for cholinergic and monoaminergic neuron-specific responses. Koyama Y, Honda T, Kusakabe M, Kayama Y, Sugiura Y (1998) In vivo electrophysiological distinction of histologically identified cholinergic neurons by extracellular recording and labeling in rat laterodorsal tegmental nucleus. Kayama Y, Takagi M, Ogawa T (1986) Cholinergic influence of the laterodorsal tegmental nucleus on neuronal activity in the rat lateral geniculate nucleus. Kayama Y, Shimada S, Hishikawa Y, Ogawa T (1989) Effects of stimulating the dorsal raphe nucleus of the rat on neuronal activity in the dorsal lateral geniculate nucleus. Kayama Y, Ohta M, Jodo E (1992) Firing of ‘possibly’ cholinergic neurons in the rat laterodorsal tegmental nucleus during sleep and wakefulness. Kayama Y, Negi T, Sugitani M, Iwama K (1982) Effects of locus coeruleus stimulation on neuronal activities of dorsal lateral geniculate nucleus and perigeniculate reticular nucleus of the rat. Jacobs BL, Azmitia EC (1992) Structure and function of the brain serotonin system. Prog Brain Res 88: 501–520Įl Mansari M, Sakai K, Jouvet M (1989) Unitary characteristics of presumptive cholinergic tegmental neurons during the sleepwaking cycle in freely moving cats. J Neurosci 2: 1786–1792Īston-Jones G, Chiang C, Alexinsky T (1991) Discharge of noradrenergic locus coeruleus neurons in behaving rats and monkeys suggests a role in vigilance. KeywordsĪghajanian GK, Vandermaelen CP (1982) Intracellular identification of central noradrenergic and serotonergic neurons by a new double labeling procedure. to induce a rapid, transient elevation of vigilance level by their phasic response to novel, unfamiliar stimuli. The cholinergic projection may have another role, i.e. A group of cholinergic neurons constitute a system to induce and maintain paradoxical sleep. Functions of the serotonergic projection are still mysterious, since its action on upper brain is inhibitory in spite of waking-specific activity of the neurons. The projection from the locus coeruleus is an arousal system, since the noradrenergic neurons are active specifically during waking, and activation of the noradrenergic projection excites upper brain structures. We have investigated functional roles of the projections by recording neuronal activity in these brainstem nuclei, and by observing effects of stimulation of the brainstem nuclei. They may function as controllers of sleep and wakefulness. Noradrenergic projection originating in the locus coeruleus, serotonergic projection from the dorsal raphe nucleus, and cholinergic projection from neurons gathering in the laterodorsal tegmental nucleus and scattering in the pedunculopontine tegmental nucleus constitute three diffuse projection systems arising from the brainstem and innervating wide areas of the brain.
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