Thanks for making me think. The Gates of Hell by Dante was the inspiration of Rodin's statue which was part of a sculpture so much more involved than just The Thinker. He is uncomfortable. His face is pained with flared nostrils and pursed lips. His toes grip the uncomfortable rock he awkwardly sits upon. His muscles are all stressed and he is twisted in such a way that does make on think.
Parhaps he is balancing ? In pain possibly? I do like the left versus right brain ideology though. Intriguing really concidering the complexity of the original piece. There is alot of pain and suffering depicted that would suggest pain and his contemplation of good vs evil. In the Bible the Right hand is of God and the left hand is for Satan the fallen. Maybe he is caught between the two?
The reference to masterbation may not be far off either concidering it was once thought of as evil but is in nature pleasurable. Religion can twist what is meant for good in nature. Dante's Inferno was the inspiration behind this.
The statue was to one of two that guard the gates of hell. The original piece by Rodin is strewn with pained bodys and sexually contorted people twisted up in innocence , women and children, intertwined with what was posed by human law as forbidden. There are some very suggestive pieces within the whole.
I believe the idea of the whole piece of art including The Thinker was to experiment and defy conformity. The poet was expressing life and using his imagination to twist the rules of nature a bit.....I read Dante's Inferno about 25 years ago and that's my take. Good memory jarring. Awesome post. Thank you. Checked out this link http://www.rodinmuseum.org/collections/collectiontheme/4.html