The EEG clearly demonstrates: The brain is very active during sleep, albeit that the activity is completely different to that in the awake state. During sleep, specific electrical currents are generated in the brain. And proteins form so that the nerve cells can link up with the aid of the so-called synapses.
There are many indications that the memory is generated during sleep – in a very real way in the form of newly connected nerve cells.This can be imagined quite illustratively, because as in a computer, there are different areas of the brain which are responsible for different tasks. The hippocampus at the very center serves as working memory for everything we experience during the day. New nerve cells and nerve connections are being formed continuously there. This means it can take in information particularly easily. But the information stored in the hippocampus can quickly be overwritten again.
This is in contrast to the neocortex, i.e., the strongly structured surface of the cerebrum. This is where the information from the hippocampus is transferred to and temporarily stored, until it is finally moved to the prefrontal cortex, our long-term storage unit. This transfer of information from one area to another takes place during sleep – controlled by the rhythmic, long wavelength brain waves.