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

Sleep has been implicated in the plastic cerebral changes that underlie learning and memory. Indications that sleep participates in the consolidation of fresh memory traces come from a wide range of experimental observations. At the network level, reactivations during sleep of neuronal assemblies recently challenged by new environmental circumstances have been reported in different experimental designs. These neuronal assemblies are proposed to be involved in the processing of memory traces during sleep. However, despite this rapidly growing body of experimental data, evidence for the influence of sleep discharge patterns on memory traces remains fragmentary. The underlying role of sleep in learning and memory has yet to be precisely characterized.

https://science.sciencemag.org/content/sci/294/5544/1048.full.pdf

The role of sleep in learning and memory.

THE human brain is the instrument of the high powers of intelligence that distinguish man from all other living creatures. The secret of man's most distinctive attribute is hidden in the texture of his brain, and perhaps will never be fully revealed. Yet from time to time, with the growth of knowledge and the discovery of new methods of approach, we can profitably return to this greatest of all biological problems and get new glimpses of the factors that have made man what he is. Two considerations make the present time appropriate for taking stock of the state of our knowledge of these matters. The emergence of a clearer understanding of the sequence of structural changes in the brain and body of man's ancestors enables us to interpret the physiological factors involved in the widening and deepening of the intellectual powers and to appreciate the conditions essential for the attainment of-such mental growth. In the second place, the new points of view regarding the functions of the cerebral cortex that have emerged from Dr. Henry Head's suggestive clinical investigations prompt one to examine the brain anew and endeavour to integrate the results of his brilliant analysis with those revealed in the study of the evolution of the brain. Whether or not it is yet possible fully to correlate the facts and conclusions of these two disciplines into one coherent body of doctrine, it is well worth while to make the attempt to do so, if for no other reason than to direct attention to new problems that call for solution.

The Human Brain

Assessing African medicinal plants for efficacy and safety: pharmacological screening and toxicology.

Sleep states and memory processes in humans: procedural versus declarative memory systems

Psychology grew out of the European and North American soil, which, according to several African authors, is impoverished in soul and poor in spirit. It is to such psychology that we in South Africa bow our heads. In doing so we do ourselves a disservice, for there is in sub-Sahara Africa a psychological dimension which has a great deal to offer the rest of the world. Southern Africa's psychological potential is especially apparent with respect to the holistic principle — the importance of the majority of her people attach to the physical, spiritual and interpersonal dimensions of being.In contrast to Africa's holistic approach the framework of ‘bigoted rationalism and fanatic adherence to outer physical reality’, characteristic of western society, has created a dehumanized psychology, particularly apparent in South Africa. Not only is there no understanding or need to understand and know about the psychological principles underlying life in Africa, but psychology seems to be oblivious to the immense huma...

Psychology in South Africa Belongs to the Colonial Era. Arrogance or Ignorance

The incidence of indigenous healing, recognition of the spiritual and emotional dimension in the lives of our population, lack of ‘professionally’ qualified mental health workers, inadequacy of imposing Western approaches on other cultures, proven effectiveness of nonprofessional workers in the mental health area, shortcomings in and disenchantment with Western models of healing and the holistic nature of indigenous healing compel cognisance. The similarity between certain Western approaches, such as that of Jung, and indigenous healing, development in brain research, humanistic and transpersonal psychology, arguments by the World Health Organization (WHO), and the call to integrate indigenous and Western approaches to healing, necessitates a closer look at the area. South African academics and professionals have urged for the recognition of indigenous healing in order to provide a comprehensive mental health service. It is felt that indigenous healing can teach us and offer unique opportunities in the ap...

Indigenous Healing in South Africa: A Neglected Potential

In the investigation of pre-sleep variables that affect sleep stage distribution and eye movement bursts during the rapid eye movement (REM) stage of sleep, 24 paid student volunteers slept three nights in the laboratory. Preceding sleep on the third night they underwent a four-hour learning task which involved either visual learning (Group VL), minimal visual learning (Group MVL), auditory learning (Group AL) or minimal auditory learning (Group MAL). Groups VL and AL showed significantly greater increases in percentage REM sleep than groups MVL and MAL from the control to the experimental night, while groups VL and MVL showed greater increases in rapid eye movement bursts occurring during REM than groups AL and MAL from control to experimental night. These results were interpreted to support the notion that memory consolidation occurs during REM sleep. It was speculated that actual eye movements represent a sensory scanning process of pre-sleep events.

REM Bursts and REM Sleep following Visual and Auditory Learning

Large lesions in the septal forebrain failed to influence the REM sleep of hooded rats under a number of different conditions. This was true whether the electrical activity of the cortex or the activity of the dorsal and ventral hippocampus were used as criteria to assess REM sleep. The amount of REM sleep of animals with and without lesions was the same under baseline and REM deprivations conditions, and also similar under conditions of different types of environmental noise. The most surprising finding was the persistence of hippocampal theta activity after septal co-agulation. As has been reported previously, REM deprivation causes an appreciable compensatory effect. The values of REM sleep obtained under baseline and deprivation conditions were comparable to that previously obtained in our laboratory.

The Septal Forebrain in Relation to REM Sleep, Hippocampal Theta and Sensory Regulation

The effects of various parameters of electric footshock on the sleep stage distribution of hooded rats were investigated in three experiments. Shock severity, rather than predictability or controllability, affected sleep stage distribution. Continued suppression of REM sleep occurred with the administration of 150, but not with the administration of 15 shocks per day. The predictability of shock onset and the controllability of shock offset, had no effect whatsoever on sleep stage distribution.

T.L. Holdstock

Papers

Psychology in South Africa Belongs to the Colonial Era. Arrogance or Ignorance

Indigenous Healing in South Africa: A Neglected Potential

REM Bursts and REM Sleep following Visual and Auditory Learning

The Septal Forebrain in Relation to REM Sleep, Hippocampal Theta and Sensory Regulation

The Effects of Electric Shock Stress on Rapid Eye Movement (REM) Sleep in Hooded Rats