GTD Times: Toning up your thinking muscles

In our recent Productive Living newsletter, David Allen talks about "Toning up your thinking muscles."  Here's a letter from Frederick Ross, a graduate fellow at The Rockefeller University who shared his perspective on the brain as a muscle.

I'm something between a theoretical physicist, mathematician, and theoretical biologist by profession, so I've had to be on very intimate terms with my thinking apparatus for many years.

The conscious, symbol manipulating part of our brain is very much like