You know head line is represent brain in palmistry so you need to check subject's head line for his metal abilities.
1) Good head line with no bad sign on it.
2) Long head line with no bad sign on it.
3) Straight head line which ends on Upper Mars denotes good memory and subject is intelligent.
4) If island and cross is present on head line then subject is weak in education.
5) If head line goes towards Mount moon then subject is creative and imaginative but if head line is straight then subject is practical.
6) If head line is connecting with life line then subject is dull and cautious but if head line is separate from life line then subject is independent thinker.
It is important that head line is good in both hands. You can also read in this post about 5 major lines on hand