In poker, we mostly use the skills from the right side of our brains to gather data. The right side of the brain notices the phenomenon of John scratching his head when he bets. But then, the left side of our brains will usually come to a better, more complete conclusion about what to do than the analogical right side will. Correct poker thinking comes from gathering data, and then putting the pieces of the puzzle together, and then making the move that is the most profitable in the long run. It's not much good to be able to discern information about our opponents, if we then don't know what to do with it.
Every poker player uses both parts of the brain.
The most left-brained person still notices when an opponent reacts as if hit by lightning when a particular card is dealt. We do use both sides of our brains. But everyone is bound to use one side either a little or a lot more than the other. People wanting to be fully-rounded, complete, winning poker players need to work on developing both sides of their brains, especially the side that does not come natural to them.