Brain Plasticity & Cognitive Abilities

I've just read Richard Nantel's post The Ultimate Pretest in which he talks about his interest in brain plasticity.

Scientists are finding ways to change the brain through intellectual exercises. People with poor auditory memory, for instance, can benefit greatly by memorizing poetry. People who are socially clumsy can be given exercises that improve their brain’s ability to read nonverbal clues.

I'm a believer in this stuff. It gives me hope that me get smarter some day. Haven't yet read that brain plasticity book, but it's on my list.

So I have no expertise in this area -- and perhaps this is really just a note to self to look into this topic more -- but I'm just wondering how brain plasticity relates to the recent NIH study out that claims that cognitive ability is mostly developed by adolescence (found via Jay Cross).

• Are brains plastic in some ways/areas of thinking, but not others?
  
• Is cognitive ability plastic? And what is cognitive ability, really?
  
• They say cognitive ability is mostly developed by adolescence -- so is that stuff no longer plastic and it's just all the rest that remains plastic?
• Or does cognitive ability actually have nothing whatsoever to do with brain plasticity -- we can form better neural pathways to better remember things, but perhaps that's not cognitive ability at all. That's just remembering stuff.
  

Me brain feels very, very small.