Brian's Brain is a cellular automaton devised by Brian Silverman, who also invented Wireworld; it became widely known through the 1980s cellular-automaton machine CAM-6 of Tommaso Toffoli and Norman Margolus. Each cell is in one of three states: ready, firing or refractory. A ready cell fires if exactly two of its eight neighbours are firing; a firing cell always becomes refractory on the next step; a refractory cell always becomes ready again.

The rule is loosely modelled on neurons, which cannot fire again immediately after a spike. Because no cell can fire twice in a row, nothing ever settles down: almost any starting pattern dissolves into a seething, never-ending storm of small “gliders” that travel in straight lines, collide, and spawn more of themselves. It is one of the simplest rules known to produce such persistent, chaotic activity, in contrast to Conway's Life, which usually freezes into still lifes and blinkers.

Here a 72 × 72 board is stepped twelve times a second with the genuine rule (the edges wrap round, so the board is really a torus). The numerals are cells removed from the game: they never fire and so act as insulating walls that the storm must flow around. The only interventions are the once-a-second discharge along their edges and, if activity ever runs low, a sprinkle of new sparks.