Behaviour results from interaction with the environment. We interact to continue gaining sensations. e. g. , taste, pheromones. Motivation allows the brain a way of setting priorities. Motivation could be described as the ability to make predictions about what is most important in a particular scenario. Motivational drives can be internal or external. Basic drives maintain homeostasis: energy, temperature, chemical balance, etc. The body can maintain homeostasis by autonomic responses, neuroendocrine responses, or behavioral responses. Nonregulatory behaviours are controlled by external cues. Hormones influence sexual behaviour through the lifespan. Emotions allow us to signal our internal state to others. The study of human emotions goes back to darwin, who suggested that emotions are constant across cultures and ages. Emotions include fear, anger, surprise, joy, sadness, and disgust. The hypothalamus and the amygdala are important limbic structures. The hypothalamus contains many different nuclei, which influence reproductive, appetitive, and agonistic behaviors.