Did you dream last night? Dreams are mysterious. Some are the reverse of real life. Some are absurd. Two different schools of thought exist as to why we dream: the physiological school, and the psychological school. Both, however, agree that we dream during the REM, or rapid eye movement, phase of sleep. During this phase of sleep, our closed eyes dart rapidly about, our brain activity peaks, and our muscles suffer temporary paralysis. The physiological theory centers upon how our body, specifically our brains, function during the REM phase of sleep. Proponents of this theory believe that we dream to exercise the synapses, or pathways, between brain cells, and that dreaming takes over where the active and awake brain leaves off. When awake, our brains constantly transmit and receive messages, which course through our billions of brain cells to their appropriate destinations, and keep our bodies in perpetual motion. Dreams replace this function. Two underpinning physiological facts go towards supporting this theory of dreams. The first lies in the fact that the first two or so years of ones life, the most formative ones for learning, are also the ones in which the most REM sleep occurs. It follows that during this time of the greatest REM sleep, we experience the greatest number of dreams. The second physiological fact that lends credence to this theory is that our brain waves during REM sleep, as recorded by machines measuring the brain's electrical activity, are almost identical in nature to the brain waves during the hours we spend awake. This is not the case during the other phases of sleep. Psychological theorists of dreams focus upon our thoughts and emotions, and speculate that dreams deal with immediate concerns in our lives, such as unfinished business from the day, or concerns we are incapable of handling during the course of the day. Dreams can, in fact, teach us things about ourselves that we are unaware of. Connections between dreams that the human psyche have been made by many people over thousands of years. Sigmund Freud, one of the fathers of modern psychology, believed dreams to be symbolic of any number of things buried deep within our minds and our memories.   note: physiological school: 生理学学派 psychological school: 心理学学派 REM: 眼球速动期   peak: 达到高潮 proponent: 支持者 synapse: 突触 brain cell: 脑细胞 perpetual motion: 永恒运动 underpinning: 基础的，支柱的   credence: 信任         psyche: 心智 Sigmund Freud: 希格蒙德弗罗伊德