The interrelated effect of sleep and learning in dogs (Canis familiaris); an EEG and behavioural study

The active role of sleep in memory consolidation is still debated, and due to a large between-species variation, the investigation of a wide range of different animal species (besides humans and laboratory rodents) is necessary. The present study applied a fully non-invasive methodology to study sleep and memory in domestic dogs, a species proven to be a good model of human awake behaviours. Polysomnography recordings performed following a command learning task provide evidence that learning has an effect on dogs’ sleep EEG spectrum. Furthermore, spectral features of the EEG were related to post-sleep performance improvement. Testing an additional group of dogs in the command learning task revealed that sleep or awake activity during the retention interval has both short- and long-term effects. This is the first evidence to show that dogs’ human-analogue social learning skills might be related to sleep-dependent memory consolidation

Is sleep's 'supreme mystery' unraveling? An evolutionary analysis of sleep encounters no mystery; nor does life's earliest sleep, recently discovered in jellyfish.

Biotelemetry has revealed daily 15-h behavioral sleep periods in a cubomedusan jellyfish, Chironex fleckeri. Its sleep is expected to be phylogenetically most primitive, since jellyfish possess only two germ layers. They belong to the phylum Cnidaria, the 'simplest' multicellular organisms with an organized nervous system. Cubomedusae have a complex visual system with 24 eyes of four different types, each type specialized for a different task. Input to these eyes during visually guided fast-swimming predation requires enormous amounts of neural processing, possibly nearly saturating the capacity of their comparatively simple nervous system. These heavy neural demands may account for the need for fifteen hours of sleep. C. fleckeri is the only animal known for which sleep may be either present or absent, dependent on lifestyle. Limited knowledge of behavior of some other cubomedusae suggests that they also possess this faculty. The finding of sleep in C. fleckeri supports current proposals of sleep's origin and basic function. Evolutionary analyses link sleep to a conflict produced by excessive processing demands on multifunctional neural circuitry for detailed focal vision by complex lensed eyes. The conflict arises between the enormous demands of complex visual analysis and needs for split-second control of actions, on the one hand, and non-urgent processing of memories of ongoing and stored events, on the other. Conflict is resolved by deferring the non-urgent processing to periods of sleep. Without sleep, selection would favor the evolution of circuitry 'dedicated' to single or but few tasks, with corresponding lesser efficiency. Had complex lensed eyes of medusae originated as a consequence of selection for increased mating success of males pursuing females, it could have occurred before the evolution of fast-swimming bilateral (three-germ-layered) prey. But if it was a consequence of selection for increased prey-hunting success, the origin of such eyes probably awaited the coexistence of bilateral prey

Sleep researchers need to bring Darwin on board: elucidating functions of sleep via adaptedness and natural selection

The development of neural multifunctionality – given brain regions carrying out more than one function – conferred great efficiency on brain function at early stages of evolution. This applied to animals that led relatively simple lives with few needs for long-term memories, such as many lower invertebrates – many molluscs, echinoderms, worms, etc. As more complex lifestyles and detailed focal vision evolved, needs for self-initiated and reflexive activities increased in frequency, and recognition of many locales, conspecifics, and other forms of life became essential. These developments were accompanied by greatly expanded needs for neural processing supporting sensory and motor activities, and establishing and storing long-term memories. Since these categories of neural processing occur in largely overlapping brain regions, brain functioning would have become increasingly maladaptive, had the evolution of these more complex lifestyles not been accompanied by compensating adaptations that obviated these potentially conflicting brain activities. These adaptations consisted of: first, restful waking; second, primitive sleep; and finally, fully developed sleep, with its specialized rapid-eye-movement and non-rapid-eye-movement states, that contribute to the maintenance of great efficiency of brain function. The only animals with detailed focal vision that can achieve highly efficient brain function without sleep, are those in which demands on memory processing are greatly reduced in consequence of routine, monotonous, almost purely reflexive lifestyles, with few needs for acquiring experiential long-term memories. The best known animals in this non-sleeping category are tunas and many sharks

Sleep researchers need to bring Darwin on board: elucidating functions of sleep via adaptedness and natural selection

The development of neural multifunctionality – given brain regions carrying out more than one function – conferred great efficiency on brain function at early stages of evolution. This applied to animals that led relatively simple lives with few needs for long-term memories, such as many lower invertebrates – many molluscs, echinoderms, worms, etc. As more complex lifestyles and detailed focal vision evolved, needs for self-initiated and reflexive activities increased in frequency, and recognition of many locales, conspecifics, and other forms of life became essential. These developments were accompanied by greatly expanded needs for neural processing supporting sensory and motor activities, and establishing and storing long-term memories. Since these categories of neural processing occur in largely overlapping brain regions, brain functioning would have become increasingly maladaptive, had the evolution of these more complex lifestyles not been accompanied by compensating adaptations that obviated these potentially conflicting brain activities. These adaptations consisted of: first, restful waking; second, primitive sleep; and finally, fully developed sleep, with its specialized rapid-eye-movement and non-rapid-eye-movement states, that contribute to the maintenance of great efficiency of brain function. The only animals with detailed focal vision that can achieve highly efficient brain function without sleep, are those in which demands on memory processing are greatly reduced in consequence of routine, monotonous, almost purely reflexive lifestyles, with few needs for acquiring experiential long-term memories. The best known animals in this non-sleeping category are tunas and many sharks