Naran
The mind operates with ego.
Which is the biggest finger? Ego must be the biggest finger, which is the middle finger.
Ego cannot work separately. It has to think. Index finger is the thinking mind. Ego is mind and mind thinks with the index finger. That is why both are close to each other.
You write with index finger. The moment you touch the pen, the thoughts flow. That means it must be the thinking finger– the finger that produces thoughts.
For the Mind to become a rational mind or analytical mind (index finger) the thumb has to join the middle finger, which represents ego, and the index finger which represents thinking.
Related Blogs
Uses of Akash Mudra: http://wp.me/ptUIh-1N
Have a higher (better) perspective: http://wp.me/ptUDX-6j