Science Daily reports:
Essentially, once the brain is triggered to reorganize its neural networks in wakefulness (by visual deprivation, for instance), intra- and intercellular communication pathways engage, setting a series of enzymes into action within the reorganizing neurons during sleep.
To start the process, NMDAR is primed to open its ion channel after the neuron has been excited. The ion channel then opens when glutamate binds to the receptor, allowing calcium into the cell. In turn, calcium, an intracellular signaling molecule, turns other downstream enzymes on and off.
This process only occurs during sleep. Read the whole thing, they have some interesting qutoes from the researchers involved speculating on the very nature of memories.
Some people complain that neuroscience research is not immediately applicable but this most certainly is: if you want to form new memories for a test you must sleep between the time that you are studying and the time of the test. This not only has implications for “all-nighters” but also for the potency of same-day studying in general.