Gameplay takes place under an electron microscope, and alternates between construction and invasion phases. During construction, players have 60 seconds to create defenses around a healthy brain cell to counter attack from viruses and bacteria. Using a drag-and-drop interface, players build a perimeter consisting of defensive walls, medical lasers, repair pylons, and other structures. During the invasion phase, players have another 60 seconds to direct the perimeter's defenses against pathogenic attack. Gameplay during this phase changes based on the perimeter's construction. A configuration that's heavy on high-powered offensive pieces will require players to micromanage their offense, while a cleverly-designed defensive configuration will require less direct attention.