What Causes Dreams: The Chemistry of Dreaming

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The human brain is a complex mechanism, and the science of what causes dreams covers a range of areas, from tracking our brain activity during REM sleep to examining the chemistry of dreaming. Although the emotional centres of our brains are buzzing with activity while we dream, the biochemistry is dramatically different to our waking state.

The chemicals which play the most important role in the science of dreams are the neurotransmitters acetylcholine, serotonin, and noradrenalin (also known as norepinephrine).

Neurotransmitters are the chemicals our nerve cells use to communicate with their neighbours. Noradrenalin and serotonin are linked with memory, attention, and concentration, and while we’re awake they’re produced plentifully in our brains. But during REM sleep, the supply of these chemicals shuts down, and acetylcholine courses through our brains.

“The brain is being squirted full of this stuff, and it drives you nuts. Your visual and emotional centers are being bombarded. You are basically having a modified seizure,” says Dr. J. Allan Hobson, Harvard Medical School dream researcher.

The bursts of acetylcholine induce REM sleep and excite our visual, motor, and emotional centers, sending images flashing through our minds, but without the serotonin and noradrenalin we lack our usual judgment and memory skills, leading to the bizarre unreality of the dream world. Injecting acetylcholine-like substances into the brains of research animals has given them longer and deeper episodes of REM sleep.

What Causes Dreams: The Chemistry of Dreaming

A low supply of acetylcholine in the brain has been linked with Alzheimer’s disease. Some drug treatments for Alzheimer’s work by preventing the breakdown of this neurotransmitter, and very vivid dreams are a common side effect of these medications.

What causes dreams? It’s pretty safe to say that the main chemical cause of dreams is acetylcholine!

After about 90 minutes of REM sleep, the serotonin and norepinephrine start pumping out again, counteracting the acetylcholine and “switching off” our dream state.

One theory is that REM sleep allows these cells to rest, giving our brains a chance to restore their supply of serotonin. This provides an interesting connection to me, as a lack of serotonin is thought to be one of the biochemical causes of depression.

So that’s the biochemical model of dreams, but what about other theories on why we dream? Dream research has plenty to say on this, particularly in the areas of learning, memory, and emotion.