Spelling

Reading over anything I write, including below posts, there are three or four words that I seem to continuously miss-spell.

there/their/they're
attachment (I want to spell it attatchment, put in a "t" like in "match")
roll/role (I did this below, and seriously in like five different appearance requests)
no/know

If any Brain Doctors are reading this, could you please tell me what part of my brain I have obviously damaged, and whether playing "Brain Age" on the PSP will help?