When you learn a new fact, there are physical changes happening in the structure of your brain. Our brain is full of vast synapses; these are tiny connections between neurons (brain cells). Memory storage depends on these synapses, but exactly how these synapses between neurons embody knowledge, or how memories get retrieved years later is a mystery at the moment.

Have you ever told yourself “That’s it-I forgot!” When trying to remember an interesting story or some fact that you know is inside your brain somewhere but you just can’t regurgitate it? Well there is actually a reason for this. The expression “Shoot! My brain cells are just not firing today” is very literal. When two cells are active at the same time, the connection between them strengthens, when one of them is not active, the connection weakens. Moreover, it turns out that the act of retrieval can destabilize the memory. When you recall a past event, the memory becomes temporarily susceptible to erasure. Moreover, it is actually possible to chemically block a memory during that time window. Now that’s a little scary especially when you know that the memory is not stable as it is.

Click here for some interactive videos that can help understand how neuron synapses work, and give a visual reference. I suggest to look at the last video first.

Source: Discover Magazine. August 2007. 10 Unsolved Mysteries of The Brain. Pg.56