Reptilian, paleomammalian, and neomammalian brain
Lower, interior brain structures, mostly part of the brain stem, form the reptilian brain. The name derives from the similarity of these structures to those in primitive animals. These structures are primarily responsible for basic bodily mechanisms, such as heart rate, and for control of instinctual urges, such as feeding. The second level of structures is the paleomammalian brain, composed of structures largely shared with early mammals. In the human, many of these structures form a system referred to as the limbic system. These structures help us respond more readily to our environment (e.g., warm-blooded) and are responsible for basic emotional responses, such as fear. The third level of structures is the neomammalian brain, consisting of the cortex which covers most of the lower centers. This we share primarily with other primates, although the human cortex is substantially more sophisticated. The cortex allows for complex thought and memory formation, and substantial control over ourselves (for example, we can in many ways "control" our emotions).