Every day, people act in response to countless external stimuli, activities in the outside world that result in a specific behavior. An oncoming car causes a pedestrian in a bustling city to jump back to the curb. Someone tells a joke that makes you laugh. You call someone's name causing that person to stop and turn around.

Though seemingly instantaneous, our responses to life's many sights and sounds are the result of neural pathways that select the information that ultimately determines our behavior. For instance, the pedestrian doesn't step back to the curb for all moving vehicles, just the one heading toward him.

How the brain identifies behaviorally useful — or ethologically relevant — information and then translates it into action has been difficult to understand. However, one of the most complete insights into this process may now have come from the tiny, relatively simple brain of the fruit fly (Drosophila melanogaster), according to a study published in the journal Neuron.

Princeton University researchers tracked the neural activity of female fruit flies being courted by males to capture the process through which an outside stimulus causes a change in behavior. They monitored the brain cells in the female's auditory pathway and could observe her neural activity from the moment a male caught her interest to when she decided to potentially mate.