The brain receives a variety of sensory information, then synthesizes and analyzes the data by sending it into various centers and loops. It then determines a course of action and communicates with others.
The microbe seems to do much of this without neurons and a brain. Individual microbes solve complex problems, such as locating food, evading predators, and communicating for complex group activity. Microbes carry out these functions using at least six capacities that we have traditionally attributed only to brains: