We can also trace this reverberation at a lower level, not at the electrophysiological level, but at the molecular level, what sorts of molecules are active inside the cells, that have to with learning so this are experiments that I did myself, and I studied two groups of rats, really rats that never left they're homecages, a very boring situation, nothing new to learn and animals that were exposed to sort of a rat disneyland, with cardboxes connected by PVC tubing and lots of new kinds of food, very scientific stuff, that allows animals to engage, and be happy stimulate their cortex and hippocampus as they explore, so after that we brought them into another chamber, recorded their sleep, waited some hours, and when they entered specific sleep stages slow wave sleep, REM sleep, as compared to waking, we looked into the expression of a gene, called zif-268 you don't need to remember this, this is a gene that is involved with the consolidation of memories it's a key gene to transform a short term memory trace into a long lasting memory trace it's typoically expressed during waking, we acquire memories during waking so we asked is this gene also active during sleep? and our findings were very exciting for us, not for the rats, what we found was that when the animals were in the boring situation, the expression of gene is very strong in the cortex, this is one hemisphere of the rat brain and in the hippocampus, this is an in situ hybridization for this gene using radioactive probes during waking you see strong expression of the gene, during slow-wave sleep the expression is very much reduced, and so it is in REM sleep 