HUMANS HAVE BEEN fascinated by dreams–and with figuring out what these nocturnal adventures might mean–for our entire history.

The Greek physician Hippocrates, hailed as the father of modern medicine, believed that dreams were an indicator of disease lurking within the body. Ancient rulers and military minds, including Alexander the Great, Hannibal, and Genghis Khan, made strategic decisions based on interpretations of their dreams. Psychoanalyst Sigmund Freud famously wrote a book aptly titled The Interpretation of Dreams in which he posited that dreams are reflections of thoughts and feelings that the ego normally represses.

Today, beliefs about the meaning of dreams are just as diverse as ever: leading theories include that dreams are communication from the brain, a form of functional data, and conscious or subconscious memories in action.

What Happens During Dreams?

Scientists have intensively studied brain activity during sleep in order to understand more about the mechanisms behind dreaming. While some functions and processes are still unknown, researchers have been able to glean a lot of information based on the parts of the brain that “light up” when subjects are dreaming. The limbic center, the part of your brain primarily responsible for controlling emotions, is the most active part of the brain during a dream. Simultaneously, the part of the brain that controls logic and reason, the dorsolateral prefrontal cortex, is suppressed, which is why dreams that seem perfectly logical while we’re dreaming sound absurd when we try to recount them later.

Are Dream Interpreters Legit?

Thanks to the internet, finding out what your latest dream means may be just a Google search away–or not. Many books and websites dedicated to dream interpretation or dream analysis are based on beliefs about symbols and motifs that are largely attributed to the work of Freud contemporary and psychoanalyst Carl Jung. Jung’s work was built on theories about archetypes and the collective unconscious, a form of “ancestral memory” that reflects experiences throughout human evolution. Much of Jung’s body of work is still well-respected today, but the problem with using his theories as a basis for universal dream interpretation is that symbology is highly dependent on specific cultures. For example, dreaming about animals like snakes or owls could be interpreted to mean wildly differing things based on the cultural background of the dreamer. Snakes and serpents can represent anything from rebirth to vengeance. Ultimately, there is no scientifically accepted “system” for accurate dream interpretation.

Keeping a Dream Diary

Dreams are highly subjective. If you’re concerned about your dreams or interested in learning more about what they might mean, try keeping a dream diary. Jot down the highlights of your dreams as soon as you wake up, and you’ll probably find that your dream recall improves with practice. Noticing recurring patterns or overarching themes in your dreams over a period of time, and examining your fears, stressors and other issues that coincide with that time period is probably a more useful tool than trying to “interpret” individual dreams.

Despite our advances in scientific understanding, the brain remains an unmastered frontier. The mechanics and functions of dreams are still largely a mystery. Whatever our dreams might mean, there’s no doubt that they will continue to entertain, puzzle, terrify, and delight humankind.