Sleep improves the consolidation of both declarative and non-declarative memories. Diekelmann and Born discuss the potential mechanisms through which slow wave sleep and rapid eye movement sleep support system and synaptic consolidation. Sleep has been identified as a state that optimizes the consolidation of newly acquired information in memory, depending on the specific conditions of learning and the timing of sleep. Consolidation during sleep promotes both quantitative and qualitative changes of memory representations. Through specific patterns of neuromodulatory activity and electric field potential oscillations, slow-wave sleep (SWS) and rapid eye movement (REM) sleep support system consolidation and synaptic consolidation, respectively. During SWS, slow oscillations, spindles and ripples — at minimum cholinergic activity — coordinate the re-activation and redistribution of hippocampus-dependent memories to neocortical sites, whereas during REM sleep, local increases in plasticity-related immediate-early gene activity — at high cholinergic and theta activity — might favour the subsequent synaptic consolidation of memories in the cortex.

The memory function of sleep

Central cholinergic pathways in the rat: an overview based on an alternative nomenclature (Ch1-Ch6).

Over more than a century of research has established the fact that sleep benefits the retention of memory. In this review we aim to comprehensively cover the field of "sleep and memory" research by providing a historical perspective on concepts and a discussion of more recent key findings. Whereas initial theories posed a passive role for sleep enhancing memories by protecting them from interfering stimuli, current theories highlight an active role for sleep in which memories undergo a process of system consolidation during sleep. Whereas older research concentrated on the role of rapid-eye-movement (REM) sleep, recent work has revealed the importance of slow-wave sleep (SWS) for memory consolidation and also enlightened some of the underlying electrophysiological, neurochemical, and genetic mechanisms, as well as developmental aspects in these processes. Specifically, newer findings characterize sleep as a brain state optimizing memory consolidation, in opposition to the waking brain being optimized for encoding of memories. Consolidation originates from reactivation of recently encoded neuronal memory representations, which occur during SWS and transform respective representations for integration into long-term memory. Ensuing REM sleep may stabilize transformed memories. While elaborated with respect to hippocampus-dependent memories, the concept of an active redistribution of memory representations from networks serving as temporary store into long-term stores might hold also for non-hippocampus-dependent memory, and even for nonneuronal, i.e., immunological memories, giving rise to the idea that the offline consolidation of memory during sleep represents a principle of long-term memory formation established in quite different physiological systems.

https://www.zora.uzh.ch/id/eprint/77770/1/physiol_rev_93.pdf

About sleep's role in memory

The organization of projections from the cholinergic neurons of the basal forebrain to neocortex and associated structures was investigated in the rhesus monkey with the help of horseradish peroxidase transport, acetyl-cholinesterase histochemistry, and choline acetyltransferase immunohis-tochemistry. Four groups of neurons contained cholinergic perikarya and were designated as Chl-Ch4. The Ch1 group corresponds to the medial septal nucleus; about 10% of its neurons are cholinergic, and it provides a substantial projection to the hippocampus. The Ch2 group corresponds to the vertical nucleus of the diagonal band; at least 70% of its neurons are cholinergic, and it is the major source of innervation that the hippocampus and hypothalamus receive from the Chl-Ch4 complex. The Ch3 group most closely corresponds to the horizontal nucleus of the diagonal band; only 1% of its neurons can definitely be shown to be cholinergic, and it is the major source of Chl-Ch4 projections to the olfactory bulb. The Ch4 group most closely corresponds to the nucleus basalis of Meynert; at least 90% of its neurons are cholinergic, and it has projections to widespread areas of cortex and to the amygdala. In fact, the Ch4 group provides the single major source of cholinergic innervation for the entire cortical surface. In this respect, it is analogous to the raphe nuclei and to the nucleus locus coeruleus, which constitute the major sources of widespread cortical serotonergic and nor-adrenergic innervation, respectively.



The extensive Ch4 group can be divided into several subdivisions. Each subdivision has a preferential set of targets for its projections even though the connection patterns contain considerable overlap. The anteromedial subdivision of Ch4 is the major source of cholinergic projections to areas on the medial aspect of the cerebral hemispheres; the anterolateral Ch4 sub-division is the major source of cholinergic projections to frontoparietal op-ercular areas and to the amygdala; the intermediate Ch4 subdivision pro-vides the major cholinergic input for a variety of dorsal prefrontal, insular, posterior parietal, inferotemporal, and peristriate areas; and the posterior subdivision of Ch4 provides the major cholinergic innervation of superior temporal and immediately adjacent areas.



The basal forebrain in the human contains a cytoarchitechture analogous to that of the monkey. The Ch4 group (nucleus basalis) of the human is very extensive and can be subdivided into the same components that were identfied in the monkey brain. Pathological changes in Ch4 neurons have been described in a variety of human disease. In Alzheimer's disease, the relatively selective depression of neocortical cholinergic innervation may be closely associated with the neuronal loss in Ch4, which has also been described inthis condition.



In the rhesus monkey, all types of cortical areas receive substantial projections from the hippocampus. Virtually all of this hypothalamic input into neocortex arises from acetylcholinesterase-rich neurons which lack choline acetyltransferase. The hypothalamocortical pathway is therefore acetylcholinesterase-rich but not cholinergic.

Cholinergic innervation of cortex by the basal forebrain : cytochemistry and cortical connections of the septal area, diagonal band nuclei, nucleus basalis (substantia innominata), and hypothalamus in the rhesus monkey

The concept of impulsivity covers a wide range of ”actions that are poorly conceived, prematurely expressed, unduly risky, or inappropriate to the situation and that often result in undesirable outcomes”. As such it plays an important role in normal behaviour, as well as, in a pathological form, in many kinds of mental illness such as mania, personality disorders, substance abuse disorders and attention deficit/hyperactivity disorder. Although evidence from psychological studies of human personality suggests that impulsivity may be made up of several independent factors, this has not made a major impact on biological studies of impulsivity. This may be because there is little unanimity as to which these factors are. The present review summarises evidence for varieties of impulsivity from several different areas of research: human psychology, psychiatry and animal behaviour. Recently, a series of psychopharmacological studies has been carried out by the present author and colleagues using methods proposed to measure selectively different aspects of impulsivity. The results of these studies suggest that several neurochemical mechanisms can influence impulsivity, and that impulsive behaviour has no unique neurobiological basis. Consideration of impulsivity as the result of several different, independent factors which interact to modulate behaviour may provide better insight into the pathology than current hypotheses based on serotonergic underactivity.

Varieties of impulsivity.

Changes in acetylcholinesterase and distribution of degenerating fibres in the hippocampal region after septal lesions in the rat.

Messaoudi, Elhoucine, Kjetil Bardsen, Bolek Srebro, and Clive R. Bramham. Acute intrahippocampal infusion of BDNF induces lasting potentiation of synaptic transmission in the rat dentategyrus. J. N...

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Acute Intrahippocampal Infusion of BDNF Induces Lasting Potentiation of Synaptic Transmission in the Rat Dentate Gyrus

Behavioral effects of selective midbrain raphe lesions in the rat.

Synaptic plasticity in the hippocampus is modulated by behavioral state.

Activity, avoidance learning and regional 5-hydroxytryptamine following intra-brain stem 5,7-dihydroxytryptamine and electrolytic midbrain raphe lesions in the rat.

Bolek Srebro

Papers

Changes in acetylcholinesterase and distribution of degenerating fibres in the hippocampal region after septal lesions in the rat.

Acute Intrahippocampal Infusion of BDNF Induces Lasting Potentiation of Synaptic Transmission in the Rat Dentate Gyrus

Behavioral effects of selective midbrain raphe lesions in the rat.

Synaptic plasticity in the hippocampus is modulated by behavioral state.

Activity, avoidance learning and regional 5-hydroxytryptamine following intra-brain stem 5,7-dihydroxytryptamine and electrolytic midbrain raphe lesions in the rat.