What happens when we dream?
A story can arise during sleep and feel real. The brain remains active.
The short answer
The brain stays active during sleep. Images, feelings and experiences can arise that we call dreams. The exact reasons for dreaming are not fully understood. A dream is not a reliable prediction.
Equal-sized adult Wusels examine a framed fantasy painting of a boat above a forest and clouds in a museum. Invented dream illustration: not a flying vehicle or a recording of a real dream. The diagram is not a personal sleep measurement. AI-created illustration, not a photograph of nature.
What the diagram shows
The diagram simplifies the process. First compare its shapes and arrows. You can read its labels in larger text below.
Read the picture labels
These are the words and sentences from the diagram above. The full explanation follows below.
- Sleep contains different periods
- Non-REM: three stages
- Transition to sleep Light sleep Deep sleep
- REM
- Rapid eye movements Active brain Often particularly vivid dreams
- Dreaming is also possible in non-REM sleep.
- How are sleep and dream memories studied?
- Measurement during sleep
- Eye movements, brain activity
- Report after waking
- What do I remember?
- Measurements are not a complete dream movie. Simplified overview; not a timetable or a personal sleep recording.
An imagined Wusel scene
Puschel and Flauschi investigate
Puschel wants to record his odd dream as a prediction. Flauschi asks what he experienced and what he dreamed. He draws separate spaces. He can tell the dream without treating it as a certain message about tomorrow.
Look closely
The two Wusels are awake, studying a framed fantasy painting in a museum. The floating boat belongs to the painted scene. The separate diagram distinguishes sleep periods, measurements and a report after waking.
An example to help you understand
During the day, draw three familiar things: a boat, a forest and clouds. Invent an impossible scene from them and label it “Invented dream story” with an adult’s help. Beside it draw an everyday scene with the boat on water. Describe the difference. This compares strange dream stories; you have not measured a real dream or proved why people dream. Nobody has to share private or upsetting dreams.
Try explaining it
Is the brain simply switched off during sleep?
Choose a), b) or c), then explain your choice.
- a)No, it stays active and dreams may arise.
- b)Yes, all nerve cells are inactive until waking.
- c)Yes, the brain was active only if we remember in the morning.
Show the explanation
Correct: a): No, it stays active and dreams may arise.
The brain stays active during sleep. Images, feelings and experiences can arise that we call dreams. The exact reasons for dreaming are not fully understood. A dream is not a reliable prediction.
Explore in more detail
Here you will find longer explanations and further details. You can explore them together.
1. Sleep is not an off switch
Even when you lie quietly in bed, your brain does not simply stop working. A night contains different sleep periods. Researchers distinguish non-REM sleep with three stages and REM sleep. A phase is a period. Measurements in deep non-REM sleep show patterns different from waking. These periods alternate several times during a night. The entire night is not the same kind of rest everywhere. Our diagram shows two kinds of periods, not an exact timetable for your bed.
2. REM: eyes can move rapidly
REM stands for rapid eye movement. During this sleep phase, eyes move beneath closed lids; measurements show an active brain. Many dreams are especially vivid then: a scene can feel very real. Dreams can also occur in other sleep periods. REM therefore does not mean every dream. Many muscles are normally deeply relaxed in this phase; we do not simply walk every dreamed route in real life.
3. Experiences can combine differently
Familiar places, people and feelings can appear in a dream. They need not fit together as they do during the day. A boat could suddenly float above a forest — our museum picture illustrates this invented scene. It does not show that a boat can fly without suitable forces. After waking we often remember only parts, or no dream at all. No memory does not prove the whole night was dreamless.
4. Why we dream remains a research question
Sleep supports learning and memory; memory means keeping information and being able to use it again. This does not prove that every dream performs a particular job. There are different proposed explanations, such as links with memories and feelings. Researchers continue investigating what each explains. They measure eye movements and brain activity, for example, and ask about memories after waking. A measuring device does not simply show the complete dream like a movie. A frightening dream is called a nightmare. If it causes distress, seeking help is right.
An optional question for further exploration
You can use the longer explanation above. This is extra, not needed for the first quiz.
An extra question
If you cannot describe a dream in the morning, does that prove your brain was switched off overnight?
Discover the answer
No. The brain remains active during sleep. A missing dream memory only means you do not currently remember a dream. It proves neither a switched-off brain nor a particular exact sleep phase.
Pictures and sources for adults
Sources for further reading
Facts checked against the specialist sources below on 12 October 2026. The Wusel scene is fictional; comparisons and simplified models are explicitly explained. Sources are in English.