Why is it that some people can memorise more things than other people?

I think language is a good index here, because to know a language you have to know thousands of words. The average person who speaks well probably knows about twenty to thirty thousand words. There was a study done recently by researchers at University College London and what they did was to look at people who were bilingual and used a brain scanner to look at the thickness of the rind, or cortex, of the brain. They then measured it in people who were monolingual and people who spoke more than one language. What they found were these obvious structural differences. The people who were bilingual had a thicker language area in the brain. So the evidence is that if you can remember more things, you train your brain and develop connections. It's those connections that probably underpin the ability to store more information and recall more information.