 How the Brain Develops This activity is a demonstration of how the brain develops. The brain grows in a sequential fashion, from the bottom to the top. It grows from the least complex part, the brainstem, to the most complex area, the cortex. The Brainstem The brainstem is found at the bottom of the skull. It controls the most basic life activities, including heart rate, blood pressure, and body temperature. The Midbrain The midbrain is found at the top of the brainstem. It controls motor activity, appetite, and sleep arousal responses. The Limbic System The limbic system is the inner central portion of the brain. It controls emotional reactivity, attachment, affect regulation, and long-term memory. The Cortex The Cortex is the top layer of the brain. It is about the same depth as that of two dimes placed on top of each other. The Cortex controls logical thinking, reasoning, abstract thought, and emotional mediation. So, from the bottom up, the parts of the brain are the brainstem, the limbic system, the midbrain, and the cortex. The Perry Model A healthy cortical modulation ratio develops when a child has a variety of emotional, behavioral, cognitive, and social experiences at key times during development. You have completed this activity on how the brain develops.