Fig. 2.
Two-stage long-term memory formation during sleep in different species. (A) In humans newly encoded episodic memories are stored for initial usage in the hippocampus (orange). During SWS they are reactivated and presumably redistributed towards long-term storage sites, mainly the neocortex (green) where they reside in more abstract and de-contextualized form. (B) Sleep is essential for the formation of imprinting memory in chicks. Imprinting memory is initially encoded in the left IMM (intermediate and medial mesopallium). Presumably during SWS occurring within 9 h after imprinting training, the imprinting memory becomes redistributed to an unknown locus termed S′, where it can be more flexibly accessed in different contexts. (As the location of S′ is presently unknown the actual placement of S′ in the figure is meaningless) (C) Similar two-stage processes of memory formation supported by sleep might be established in song learning birds (not shown) and in bees during extinction learning. In bees, classical olfactory reward conditioning of the proboscis extension response occurs at the level of the antennal lobe and is not affected by sleep. However, extinction learning of this response requires sleep. We speculate (indicated by “?”) that sleep-dependent consolidation of extinction originates from the redistribution of representations (related to the conditioned response and its inhibition) from the antennal lobe to the mushroom bodies, which is a higher order processing area containing more flexibly controlled memory representations. Representations in the mushroom bodies are known to be sensitive to sleep effects. Respective upper panels provide anatomical locations for the relevant structures. (A) and (B) modified from Jarvis et al. (2005). (C) modified from Menzel et al. (2006). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)