disposed of during REM sleep. This theory solves the brain information storage problem, as our cortex would need to be much larger due to the inefficient storage of information. It also explains why we forget dreams extremely easily. Objections to the theory of reverse learning One problem for reverse-learning theory is that dreams are often organized into clear narratives (stories). It is unclear why dreams would be organized in a systematic way if they consisted only of disposable parasitic thoughts. It is also unclear why babies sleep so much, because it seems they would have less to forget. Additionally, the brain of the echidna has far less folding than the brains of other mammals, so has less surface area (the location of the neo-cortex). It may actually have less capacity for higher thought than that of other mammals, rather than more, as its greater mass suggests. In response to these objections, Crick and Mitchison proposed that the principal target for the unlearning process could be obsessive memories (strong attractors) and that the dream/REM purpose is to equalize the strength of memories. A computational model by Kinouchi and Kinouchi (2002) implementing a chaotic itinerancy dynamics in a Hopfield net shows that the Crick-Mitchison unlearning mechanism produces a trajectory of associated attractors ("a narrative") where the strong ("emotional", "obsessive" or "overplastic") memories have their dominance downplayed and an equalization between memory basins produces a better recovery of memories not recalled during the "dream". It is argued that fetuses and babies sleep so much to downgrade ("unlearn") the force of synapses present in these developmental phases. See also Francis Crick: Neuroscience and other interests References External links Sleep