EEG: Visualizing your brain asleep

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EEG: Visualizing your brain asleep

The human brain has approximately one hundred billion neurons, which communicate with each other by sending electrochemical signals. It is possible to measure these signals by placing electrodes on the surface of the skull. This method is called “electroencephalography” (or EEG) and the readings acquired from this process are known as brain waves. 


Electroencephalography is the most commonly used method in labs to measure sleep. The Dreem headband uses the same method to measure brain activity during the night and is able to precisely track sleep stages during the night.

What do brain waves mean?

Their amplitude (i.e. how high they are) is an interesting indicator. It primarily measures the synchronization of neurons with each other, that is, how well they are coordinated in their actions. The greater this amplitude is, the more it means that neurons work in rhythm.

How and why does cerebral activity vary?

During wake state, neurons work altogether at different rhythms, sending out messages in all directions: brain waves that result from this activity are small and quick.


EEG activity characteristic of arousal (simulation)

When we sleep, our brain is still active, but in a very different way. Sleep has 4 stages that can also be classified into two types: non-REM sleep (from light sleep to deep sleep, about 75% of total night time) and REM sleep (25%). Both have a recognizable pattern of brain waves.

During non-REM, ample and slow waves

During non-REM sleep, brain waves become more and more ample and slow. The peak is reached in deep sleep, with very slow, very high brain waves: they are called “slow” or “Delta” waves.

 EEG slow waves
EEG characteristic of deep sleep (“Delta” waves, very ample and slow) (simulation)

The high amplitude of these Delta waves indicate that the neurons are strongly synchronized during deep sleep: entire neuronal zones light up and then shut down successively. The Dreem headband improves synchronization of neurons by helping the brain “beat the rhythm” more effectively.

What is the role of neuron synchronization? 

According to a widespread scientific agreement, this synchronization allows the sorting and consolidation of recent memories. The slow waves allow transfer of recently learned information from the hippocampus (seat of “living memory”) into the cortex (the seat of abstract intelligence and long-term memories).


During REM sleep, small and close brain waves

REM sleep is another “type” of sleep. Unlike non-REM sleep (and especially deep sleep), its cerebral waves are very small and close, a sign that neurons work in all directions, with no precise rhythm. They almost look like those that are measured during wake state.

It has long been thought that the main role of REM sleep was the consolidation of procedural memory (memory of physical movements and know-how), whereas the role of deep sleep would rather be the consolidation of declarative memory (facts and events). However, this theory has recently been called into question. Truth is that we’re still exploring the link between the brain activity of sleep and its role.


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