Which nation from the Pacific region is the only one in the world to be in all four cardinal hemispheres?

Kiribati.

What we learn make our brain grow differently. Yes or no?

Yes. A study on London taxi drivers has shown that they have a larger hippocampus compared to bus drivers in the same city. The reason has been associated to taxi drivers having to navigate different routes each day whereas bus drivers tend to drive on the same route every day. You can read more here.