Brian's Brain is a cellular automaton devised by Brian Silverman. As in Conway's Game of Life, every cell of a grid looks at its eight neighbors, but here a cell has three states instead of two:

• Off (dark): the cell is at rest. It starts firing when exactly two of its eight neighbors are firing.
• Firing (white): in the next generation the cell is always dying.
• Dying (orange): the cell cannot fire. In the next generation it is off again.

All cells change at the same time, based on the previous generation. The cells are often compared to nerve cells, which fire and then need a moment of rest before they can fire again.

Because a cell that has just fired must rest, activity cannot stay in place: it keeps moving away from the dying cells behind it. Almost every pattern travels across the grid. The smallest is a glider of two firing cells side by side, followed by two dying cells, which moves one cell per generation. Where moving patterns meet, they explode into new sparks and long diagonal waves, so a random start turns into restless chaos.

Choose Spark in the middle to watch a small random square spread over an empty grid. To light your own sparks, choose Firing cells under Draw and drag over the grid with the mouse or a finger; Clear empties the grid first. The grid wraps around at its edges, so whatever leaves on one side comes back on the other.

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