Abstract and Keywords
The drive for regular sleep is present in many, if not all, species and is assumed to be under the control of homeostatic and circadian systems, developed in response to a need to adjust to geophysical (climatic, seasonal, and environmental) features of the environment. Given that so much study time has been invested in the assumption that to take away the opportunity for sleep will reveal the very essence of the need for that process, very few researchers have questioned the validity of this approach. Yet sleep loss, for many species, is costly and stressful, and in the laboratory setting the emotional or motivational components of cognitive deficits remain largely unmonitored. An evolutionary approach to understanding the functions of sleep assumes that clues lie in studying differences in how sleep has developed between species and under differing environmental conditions. This approach has provided important insight, but there are difficulties in making comparisons between species of widely differing physiological makeup and complexity. Interest in the relationship between sleep and memory processes has grown rapidly in recent years, and there is a sense that we have reached a breakthrough in our understanding of the functions of sleep. However, while key researchers argue that sleep is an essential state for optimal efficiency in the processing of memory, others remain unconvinced and see sleep as, at best, favorable but not essential to the consolidation and enhancement processes presumed to underpin memory.
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