Dreams and Evolution: Why the Brain Runs a Theatre We Never Commissioned

Level: expert · Topic: evolutionary neurobiology, REM function, neural basis of dreams

Dreams are the most personal and most mysterious thing the brain produces. For millennia they were interpreted as messages from gods, prophecies of the future, revelations from the unconscious. In the twentieth century, Freud offered one theory, Jung another. Today neuroscience offers answers no less remarkable — but grounded in data rather than interpretation.

Part 1. What Happens in the Brain During Dreaming

Dreams occur primarily during REM sleep, though they can happen in other stages (especially N2 — often imagistic, without narrative). The neural picture of REM sleep is unique:

• Activated: visual cortex (V1, V2), limbic system (amygdala, hippocampus, cingulate cortex), motor regions. This explains why dreams are visual, emotionally charged, and feel like real movement.
• Suppressed: dorsolateral prefrontal cortex (dlPFC) — the 'gatekeeper' of logic and self-awareness. Its silence explains why we do not notice the illogicality of dreams and do not realise we are asleep.
• Acetylcholine — the dominant neurotransmitter: it suppresses noradrenaline and serotonin (active during wakefulness) and 'switches on' REM. This is why antidepressants that block serotonin reuptake (SSRIs) suppress REM: they keep serotonin high, preventing acetylcholine from dominating.

Part 2. Three Leading Theories of Dream Function

Theory 1. Emotional therapy (Matthew Walker, Rosalind Cartwright)

During REM sleep, the amygdala — the centre of emotional reactivity — is active, but noradrenaline (the stress neurotransmitter) is at its minimum. This is a unique combination: the brain 'replays' emotional memories in a neurochemically safe environment stripped of acute stress.

Neuroscientist Matthew Walker proposed the formula: 'Sleep is therapy without the co-pay.' His data show that people who re-encountered emotional events after REM sleep rated them as less painful than those who re-encountered them during wakefulness. REM literally 'softens' the emotional charge of a memory while preserving its informational content.

Theory 2. Threat simulation (Antti Revonsuo)

Finnish neuroscientist Antti Revonsuo proposed in 2000 an evolutionary theory of dreaming: dreams are a threat simulator. Throughout human evolution, night was dangerous. A brain that 'practised' recognising threats and formulating responses during sleep had a survival advantage.

Evidence for this theory:

• Threats appear significantly more often in dreams than in real life — particularly threats relevant in our evolutionary past (falling, being chased, physical attack).
• People who have survived real threats (war, violence) show a sharp increase in nightmares with thematically similar content — the brain 'rehearses' a response to the specific threat.
• Children have more nightmares than adults — possibly because they need more 'practice' for threats they have not yet encountered.

Theory 3. Creative recombination (Robert Stickgold, Deirdre Barrett)

In wakefulness, the brain processes information primarily associatively: new material is connected to similar existing material. During sleep — and especially in REM — it operates in a 'free association' mode: unexpected links between unrelated concepts arise more easily because the dlPFC, which normally 'censors' them as illogical, is silent.

This explains the phenomenon of 'idea incubation during sleep':

Part 3. Why We Don't Remember Most Dreams

Most dreams do not reach long-term memory — and this is not accidental. For a memory to form, hippocampal and dlPFC activation is required. During REM, the dlPFC is almost completely offline. A dream is preserved in memory only if:

• waking occurs within a few minutes of the REM episode;
• the dream content is emotionally intense (activating the amygdala strongly enough to engage the hippocampus);
• waking is gradual — without the sharp sound of an alarm (which immediately activates noradrenaline and 'blows away' the neural trace of the dream).

A practical takeaway: if you want to remember a dream — do not move for the first 30–60 seconds after waking. Lie still and 'scroll through' the images. Then write them down immediately, before any other action.

Part 4. Lucid Dreaming: The Neurobiology of Conscious Sleep

Lucid dreaming is a state in which a person is aware they are dreaming and can influence the content of the dream. Neurobiologically, this corresponds to reactivation of the dlPFC during REM — that is, a partial return of the 'critical observer' to an active state.

fMRI studies (Voss et al., Nature Neuroscience, 2009) confirmed: during lucid dreams, the dlPFC is significantly more active than during ordinary REM, but less active than during wakefulness. This is an intermediate state of consciousness — a unique biological phenomenon.

Prevalence of spontaneous lucid dreaming: approximately 55% of people have had at least one lucid dream in their lifetime; around 23% experience them once a month or more. There is evidence that lucid dreaming can be trained through techniques such as WILD, MILD, and transcranial electrical stimulation (experimentally).

Conclusion: Sleep as Biological Necessity, Not Weakness

Over twelve episodes, we have travelled from Egyptian pregnancy tests to the neurobiology of dreams, from Phoenician traders to germline editing. The connecting thread is DNA: a molecule that stores the history of our species, governs the biology of each of us, and is now open to investigation as never before in human history.

Sleep is a fitting final subject. Because sleep is the moment when the genome is given the opportunity to do its work undisturbed: to repair, restore, process, remember. Those eight hours that seem like 'lost time' are perhaps the most productive hours in the biological sense.

Watch for the next season of MAPASGEN.

MAPASGEN — the podcast about genetics that is already reshaping your life.