wikipedia

… goal-directed decision-making during the hunt for food is performed by just two neuron types. Through measuring the action potentials between neurons, just two neurons were able to come to a complicated form of decision making. One neuron in the brain tells the snail if food is nearby, the second neuron signals whether the snail is hungry or not. Such decision making helps the snail save energy by reducing complex brain activity when there is no food nearby and adapts its behavior in the absence of food. Thus the snail can switch between a low-use mode and a high-use mode depending on the decision.