|MadSci Network: Neuroscience|
Generally, there is evidence that memory consolidation occurs, and that it occurs over days or weeks. To "consolidate" means to join together into one whole. MIT's Dr. Susumu Tonegawa, Nobel laureate in physiology & medicine (http://web.mit.edu/clm/rese arch_tonegawa.html), defines memory consolidation as "the process of the conversion of protein synthesis-independent short term memory to protein synthesis-dependent long term memory". That is, when we are trying to keep something in memory (like when you look up a phone number but haven't dialed yet), a set of brain cells related to that "short-term" or "working" memory stay active the whole time in what Tonegawa refers to as "protein synthesis-independent short term memory". But when we learn something, either by studying or just because it is very memorable, it is stored in what Tonegawa refers to as "protein synthesis-dependent long term memory". Rather than the nerve cells being continuously active, they modify the proteins they express, causing the long-term changes in cell function that underlie memory consolidation.
There is a great deal of information about memory consolidation available in print and on the internet, so rather than answer all of your questions I have referred you to some sources; you can also try 'memory consolidation' as a search term on most search engines. A nice discussion of short and long term memory is at http:// www.indiana.edu/~iuepsyc/P103/mem/mem.html.
Whether memory consolidation occurs during sleep is being debated ( http: //www.med.harvard.edu/publications/Focus/Mar19_1999/psych.html, http://www.sleeph omepages.org/SRS/srs/Buzsaki.htm, http://w ww.cogsci.soton.ac.uk/bbs/Archive/bbs.vertes.html ), and memory consolidation occurs during the awake state as well (http://www.jhu.edu/~jhumag/1 197web/tech.html).
Some other reputable web pages about memory consolidation are:
Try the links in the MadSci Library for more information on Neuroscience.