Towards an Evolutionary Theory of Sleep and Dreams

Towards an Evolutionary Theory of Sleep and Dreams,Sidarta Ribeiro

Towards an Evolutionary Theory of Sleep and Dreams   (Citations: 6)
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Despite the importance of sleep and dreams for the understanding of human consciousness, science is yet to achieve a consensus about their functions and intricate phenomenology. This paper outlines an evolutionary theory that is compatible with several basic observations regarding sleep and dreams. The theory proposes that slow- wave (SW-) sleep evolved from mere rest in early reptiles as a prolonged and quiescent offline state able to promote calcium-dependent memory consolidation. This cognitive role is performed by incre ased reverberation of waking patterns of neuronal activity during SW-sleep. Rapid -eye-movement (REM -) sleep, a second offline state, characterized by high cerebral activity and maximum sensory disconnection, evolved in early birds and mammals as a post-SW-sleep mini-state, lasting just a few seconds. Despite its short duration, REM-sleep is capable of boosting memory consolidation by activating genes linked to synaptic plasticity. At some point, mammals evolved extended single REM episodes, prolonging the non-stationary neuronal reverberation that characterizes REM -sleep to promote memory restructuring rather than memory stabilization. Dreams as vivid narratives that unfold in time arose as a by-product of neuronal reverberation during extended REM -sleep. Due to such non-stationary reverberation, dreams are hyper-associative strings of fragmented memories that simulate past events and future expectations, enacting possible solutions for cognitive challenges facing the dreamer. Though probabilistic, dream simulations can at times yield accurate predictions of future events. Under increased brain metabolism, it is possible to experience an enhanced REM-sleep state in which dream events are under partial or total
Published in 2004.
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