Fear of Getting Dumber

For the past five years I've had this growing fear of becoming dumber as the years go by.  I feel that I burn out faster, my memory isn't as reliable, I can't write as well as I used to and I suck more and more at puzzles and such.  I've noticed more pronounced deterioration of intelligence in a lot of my friends once we graduated from college and my greatest fear was that this might happen to me too.  My best friend has the same fear.  And he even has a theory:  He believes that most of us get jobs that are not as intellectually demanding as the courses we took in college so that certain abilities fell victim to atrophy.  He also has a job that isn't too taxing on the brain so he combats this trend by reading as much as possible and engaging in mind games, puzzles and riddles as much as he can.

My language skills have been deteriorating.  I used to have an auditory memory and a pretty-close-to photographic memory.  As a parlor trick in college, my friends would have me go around the room at a party, point out when and where I met each person, what they were wearing, and what we talked about.  30-50 people, no problem.  I used to memorize music in 1-2 sittings.  My concentration has been wavering more and more. 

I am about to go into the most mentally demanding pursuit to date(conducting) and I need these skills more than ever.  More importantly, my self esteem sure takes a beating just thinking about this.  I've relied on my intelligence more than anything else in my life.  Physically, I've never been very strong and have had a slew of minor ailments throughout life.  My EQ is not very good, to say the least.  For this reason, I've avoided activities where one needs to relie heavily on both intelligence and emotional acuity such as gambling and playing the stock market.  Within a group of people, I am usually one of the smarter people in that group and when I'm not, I really push myself in order to keep up with peers with superior abilities and usually fare pretty well without any concern of being an inferior.  It is a bit scary knowing that your strongest trait is gradually diminishing.