I've also thought of the idiom as "to rack one's brain", and the frequent ocurrences of wrack I've seen I've dismissed as probably an eggcorn - although I confess I can't see why anyone would think that seaweed would make any more sense.
I've just done some Googling and found that the same site seems to give contradictory answers: this page seems to say that either is correct "according to the Oxford dictionary online" - they don't say which Oxford dictionary. This page, however, says that "rack" [only] is correct.
What is your usage? If there's anyone with access to the OED online what does that say?
Build a man a fire and he's warm for a day. Set a man on fire and he's warm for the rest of his life.
I've always thought it was only rack. I've gone through all the verb definitions for both rack and wrack in the online OED, and only found rack used that way. Here is that citation:
quote:
d. to rack one's brain (also wit, memory, etc.): to make a great effort to think of or remember something. 1583 W. BYRD in E. Farr Sel. Poetry Reign Elizabeth (1845) I. 224 Racke not thy wit to winne by wicked waies. c1680 W. BEVERIDGE Serm. (1729) I. 193 They rack their brains..they hazard their lives for it. 1713 R. STEELE Guardian No. 47. {page}7 She racked her invention to no purpose. 1768 F. BURNEY Jrnl. 30 May in Early Jrnls. & Lett. (1988) I. 6, I have rack'd my brains half an Hour{em}in vain. 1831 Society 1 216 Fanny was racking her brains for something to say. 1880 L. STEPHEN Alexander Pope iv. 82 Racking his wits to contrive exquisite compliments. 1947 A. KOESTLER Darkness at Noon (1964) III. iii. 159 He racked his memory, but could not place anywhere this apparition. 1990 Stud. Eng. Lit. (Eng. Lit. Soc. Japan) (Eng. No.) 24 The English court racked its brains over the questions of guests and dates of performance.
