To rack one’s brain means to strain mightily to think of something or remember something. The term rack one’s brain dates back to the 1600s. The word rack comes from the Old English word recken, meaning to stretch out. When the Medieval torture device known as the rack came into use, then the meaning of the word rack expanded to denote suffering or causing harm, as well as the original meaning, to stretch out. Related terms are racks one’s brain, racked one’s brain, racking one’s brain. In some cases, the plural form of brain is used, as in rack one’s brains. The Oxford English Dictionary accepts the alternative spelling wrack one’s brain, but considering the etymology of the phrase, most writers consider rack one’s brain to be the correct spelling.
Examples
“I was trying to rack my brain for something extra special to do and suddenly a song came on the radio and I had an idea,” Lind said. (The Forest Lake Times)
So authoritative is the position of therapist that I had to rack my brain a moment before I could confidently say “no”. (The Guardian)
When asked what he used to perform the abortion, the suspect who unsuccessfully racked his brain to recall the name of drugs he administered, said he just gave her some pills. (Vanguard News)
Senior Daniel Ochefu racked his brain trying to think of all the suits he’s seen over the past four years, coming to the conclusion he doesn’t think he’s ever seen Wright wear the same suit twice. (USA Today)
In his younger days, if there was something so noticeably off about Jimmie Johnson’s No. 48 Lowe’s Chevrolet the way it was at the end of Friday’s practice session for the New Hampshire 301, Johnson would’ve spent hours wracking his brain to figure out what the issue was. (The Boston Globe)