Verified by 
1. What are dreams?
Dreams are mental experiences that occur while we are asleep. We know of the existence of dreams because most of us report having mental experiences such as thoughts, images, and emotions while asleep—and we can see consistent areas of the brain become activated during dream-sleep.
2. Why do we dream?
There are many theories, but nobody truly knows. Some researchers believe dreams have no function. Others believe that they serve to process intense emotions, or that they facilitate consolidation of emotional memories.
Still others believe that they protect sleep via hallucinatory fulfillment of a libidinal wish. And some believe that dreams simulate daytime threats so that we become better at avoiding them. (This latter theory appears to predict opposite dream content effects from those of the libidinal wish fulfillment theory.)
Some believe dreams function to run counterfactual simulations to daytime events (or possible daytime events) so that we learn from them. And some believe that dream content functions to promote emotional attachment patterns with others. There are many other theories of dream function but all of those mentioned here do have some limited empirical support.
3. Does everyone dream?
No. There appears to be a very small number of people who can recall very few dreams, if any. The fact that such people can function perfectly well without recalling any dreams suggests that conscious recall of dreams may not be required for normal brain function—unless these people (who appear not to dream) have developed some compensatory brain processes that perform whatever functions dreams normally perform, such as consolidation of emotional memories. The idea would be that if the vast majority of people consolidate their emotional memories via dreams, a small number of people who do not dream would have to have developed alternative means for consolidation of emotional memories.
4. How long do dreams last?
Nobody knows for sure. Rapid eye movement, or "REM" sleep, the form of sleep associated with vivid dreaming, can last up to about 45 minutes but we really have no definitive method for timing dreams.
Subjective estimates of dream length, however, are proportional to length of dream reports. This is consistent with the theory that dreams can last a long time rather than flash by in an instant as some early dream theorists conjectured.
The fact that dreams have substantial duration suggests that the events in dreams should be densely populated with events, people, happenings, and other elements common to normal daytime experiences. Our dream reports, however, typically lack the extensive details normally associated with dense real-life experiential episodes.
5. Are dreams meaningless?
It is unlikely that dreams are meaningless—very few, if any, are random assemblages of images. Instead, most dreams are structured into narratives. Some dreams (dreams that tend to be associated with N3 NREM sleep) can lack narrative action and instead are just presentations of a visual scene or a single set of thoughts. Still, even these non-narrative dreams are not meaningless to the dreamer.
6. What are most dreams about?
Various types of dreams cannot be reduced to this formula, but nevertheless, content analyses of thousands of dream reports from people of all ages and walks of life substantiate this basic claim: Most dreams depict people familiar to the dreamer interacting in various ways with the dreamer.
7. What are lucid dreams?
Lucid dreams are dreams during which the dreamer is aware that he or she is dreaming. Not surprisingly, properties of lucid dreams differ significantly from ordinary dreams. Most importantly, some prefrontal neural networks exhibit higher activation levels in lucid dreams relative to ordinary non-lucid dreams.
8. What are nightmares?
Nightmares are scary or terrifying dreams that typically occur in REM sleep and leave the dreamer shaken or disturbed to some extent upon awakening. Some researchers maintain that for a dream to be a nightmare it has to be disturbing enough to awaken the dreamer. Other experts point out that many non-scary dreams (erotic, sad-nostalgic, creative, spiritual) can be intense enough to awaken the dreamer, so the awakening criterion is not empirically adequate for nightmares.
9. What are the most common dream disorders?
The most common dream disorders are:
- Anxiety dreams (often associated with slight sleep in insomnia)
- Recurrent nightmares
- Repetitive dream themes
- REM Behavior Disorder (wherein the dreamer acts out his dreams)
- Dreams of depression (empty emotional content)
- Vivid fantastic dreams that may portend illness of some kind, occasionally including psychosis.
10. How can I remember more of my dreams?
Keep a dream diary handy next to your bed and get in the habit of recording dreams upon awakening. Online dream posting websites can also make regular dream recording easy.
11. Do animals dream?
There is no scientific consensus on whether animals dream. Animals do experience REM sleep and sometimes it appears that their bodies react as though they are dreaming while asleep. Given that mental simulations automatically occur when higher cortical centers are activated in humans, it seems plausible that animals also “experience” mental simulations when their brains are activated, as in REM.
12. What part of the brain lights up when we dream?
Neuroimaging studies of people in REM suggest that the limbic system is especially active during REM, with the amygdala undergoing intense activation during REM.
