One interesting problem in systems neuroscience is how the nervous system’s motor output interacts with its sensory systems. Sensory inputs that result from motor commands must be either filtered out or used to guide future motor actions. In other words, the organism must distinguish between sensory inputs that are self-generated and those from the outside world. In the juvenile songbird, for example, motor commands for song generation must be sent to some internal critic (likely basal ganglia) so the bird can compare the actual song output to some internal tutor model and improve subsequent renditions.