Understand capability is very poor.

Hi Sir/Madam, my brother having a problem in understanding the things and not be able to realise the nature and acts of human beings.. he is physically very healthy but mentally weak.. ex. He can do calculations and can't remember the values and he is not be able to understand if we tells a story also. He is interested in watching movies and serials but if we ask any questions like who they are and what is happening, he is not able to tell because he couldn't understand.. What ever he reads even though if it's a paragraph he can able to replicate them exactly but he doesn't know what actually it is and why he is studying this.. Can anybody please help me to understand what kind issue he has and what treatment we can give..