First: The number of synaptic connections doesn't really determine memory capacity. It's much, much more complex than that. In terms of relating brain physiology to memory skill, we know the hippocampus is important (because those with damage to their hippocampus have problems with memory), but...
This is an interesting question, I never considered the upper limit of charge before. After a bit of searching, I found this paper:
http://erps.spacegrant.org/uploads/images/images/iepc_articledownload_1988-2007/2009index/IEPC-2009-010.pdf
The mention three phenomenon which you may be...