From Scientific American:
Making memories seems like a difficult proposition given that our synapses are constantly in action. These connections between nerve cells in our brain, which are regularly passing chemical messages back and forth, also supposedly have our memories distributed across them. Yet, regardless of the perpetual exchange of molecules, our memories remain stable. According to a pair of researchers at the University of Utah, it is the presence of scaffolding proteins in the synapses that anchor our life lessons within the chaos of brain activity.
“You need these scaffolding proteins, number one,” Bressloff remarks. Beyond that, he continues, “at the timescale of hours, scaffolding proteins can be moved in and out, so again things would lose the memory, so you need something else, like changing the actual structure of the dendritic spine.” Like a number of other topics in neuroscience, whether the spine shifts shape or, possibly, new proteins are synthesized, how memories are formed for the long-haul is still up for debate.
More here.