Sleep is for unfinished business growing evidence that sleep is important for learning and memory

Support for a function of sleep as serving synaptic network remodeling spans studies from c elegans to the human. Here we review evidence from rats, cats, and birds that demonstrates physiological aspects of sleep, particularly REM sleep, that may uniquely serve synaptic network remodeling. We will review this evidence supporting our synaptic network remodeling hypothesis through the lens of a conceptual model demonstrating how the absence of the neurotransmitters noradrenalin and serotonin and the presence of acetylcholine and brainstem reticular activity during REM sleep make that state uniquely capable of weakening as well as strengthening synapses in a memory network. We will show how memory storage requires both pruning of unnecessary connections and potentiating others to reshape the network in the process of consolidating memories. Whereas the waking state is excellent for strengthening synapses during learning, experiments show that the neurochemical environment of waking discourages the other side of the bidirectional plasticity coin: synaptic weakening and pruning. The bidirectional plasticity that is uniquely allowed during sleep is essential for reforming memory networks during memory consolidation and reconsolidation in the presence of new information. We will discuss the kinds of learning that should require such remodeling for memory storage and the kinds (e.g. striatum-dependent) that may not require sleep in light of the physiologic model proposed