Sigmund Freud published his classic book, "The Interpretation of Dreams". In this book, he told us that dreams can be interpreted as a way to reveal the unconscious. His theory is that dreams are similar to daydreams. A dream while sleeping is something to do with wishes that are forbidden or repressed. And images in the dreams have deep symbolic meaning. And they tried to reach a compromise for the wish to be expressed safely. According to Freud, there are two levels to every dream: the manifest content and the latent content. If a student concerned about an exam very much, the student might dream about the exam: the manifest content would be a hurdle in the race for example, while the latent content would be the exam. But there is a different point of view. Hobson and McCarley disagree with Freud. They are sure that dreams are controlled from brain stem. The chemicals in the stem control the firing of certain neurons. But the message doesn't transfer to the body, because the person is sleeping, then dreams occur.

Freud talks about the drams on the psychodynamic theory, while Hobson and McCarley do it on neurophysiologic theories.