Mental puzzles are supposed to be good for the brain, but for one young man they had a surprising side effect: seizures that made his left arm jerk and twitch. The seizures started shortly after the 25-year-old student was buried in an avalanche, where his brain was deprived of oxygen for 15 minutes. Several weeks later, the tremors came on when he tried to solve a sudoku puzzle, researchers report today in JAMA Neuroscience. Sudoku puzzles are 9-by-9 grids with numbers in some of the squares; to solve them, a person must fill in the other squares with the right pattern of numbers. According to neurologist Berend Feddersen from the University of Munich in Germany, who is first author on the paper, the man tried solving the puzzles by imagining them in 3D. The harder he focused, the more his arm moved. Based on MRI scans, the researchers attribute the seizures to damaged inhibitory fibers on the right side of the man’s central parietal cortex, a brain region near the crown of the head. The unusual case suggests that when inhibitory fibers are damaged, brain activity in one area can spill into neighboring areas—in this case, the part of the brain that that controlled arm movement, Feddersen says. Despite this damage, the solution was simple: The man stopped tackling sudoku puzzles, and has been seizure-free for 5 years.