science

Reverse learning

Reverse learning is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Reverse learning rather than just read about it. In short: Reverse learning is a neurobiological theory of dreams. In 1983, in a paper published in the science journal Nature, Crick and Mitchison's reverse learning model likened the process of dreaming to a computer in that it was "off-line" during dreaming or the REM phase of sleep.

Key takeaways

Reverse learning belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Reverse learning to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Reverse learning from memory before moving on to harder problems.

Reference excerpt

Reverse learning is a neurobiological theory of dreams. In 1983, in a paper published in the science journal Nature, Crick and Mitchison's reverse learning model likened the process of dreaming to a computer in that it was "off-line" during dreaming or the REM phase of sleep. During this phase, the brain sifts through information gathered throughout the day and throws out all unwanted material. According to the model, we dream in order to forget and this involves a process of 'reverse learning' or 'unlearning'. The cortex cannot cope with the vast amount of information received throughout the day without developing "parasitic" thoughts that would disrupt the efficient organisation of memory. During REM sleep, these unwanted connections in cortical networks are wiped out or damped down by the Crick-Mitchison process making use of impulses bombarding the cortex from sub-cortical areas. The Crick-Mitchison theory is a variant upon Hobson and McCarley's activation-synthesis hypothesis, published in December 1977. Hobson and McCarley hypothesized that a brain stem neuronal mechanism sends pontine-geniculo-occipital (or PGO) waves that automatically activate the mammalian forebrain. By comparing information generated in specific brain areas with information stored in memory, the forebrain synthesizes dreams during REM sleep.

Crick verbatim on the function of REM sleep Suppose one did not have REM, then one would mix things up. That is not necessarily a bad thing — it is the basis of fantasy, imagination, and so forth. Imagination means seeing a connection between two things that are different but which have something in common which you had not noticed before. If one had too much REM, one would predict one would be a rather prosaic person without too much imagination. But the process is not 100% efficient. If one goes on too far, one begins to wipe out everything. Another way to look at it is to say "How could you prevent the brain being overloaded"? One way would be to make it bigger, to have more neurons. So perhaps the important thing to say is "The function of REM is to allow your brain or your cortex to be smaller".

Support for the theory of reverse learning In the echidna, a primitive egg-laying mammal that has no REM sleep, there is a very enlarged frontal cortex. Crick and Mitchison argue that this excessive cortical development is necessary to store both adaptive memories and parasitic memories, which in more highly evolved animals are disposed of during REM sleep. This theory solves the brain information storage problem, as our cortex would need to be much larger due to the inefficient storage of information. It also explains why we forget dreams extremely easily.

Objections to the theory of reverse learning

One problem for reverse-learning theory is that dreams are often organized into clear narratives (stories). It is unclear why dreams would be organized in a systematic way if they consisted only of disposable parasitic thoughts. It is also unclear why babies sleep so much, because it seems they would have less to forget. In response to these objections, Crick and Mitchison proposed that the principal target for the unlearning process could be obsessive memories (strong attractors) and that the dream/REM purpose is to equalize the strength of memories. A computational model by Kinouchi and Kinouchi (2002) implementing a chaotic itinerancy dynamics in a Hopfield net shows that the Crick-Mitchison unlearning mechanism produces a trajectory of associated attractors ("a narrative") where the strong ("emotional", "obsessive" or "overplastic") memories have their dominance downplayed and an equalization between memory basins produces a better recovery of memories not recalled during the "dream". It is argued that fetuses and babies sleep so much to downgrade ("unlearn") the force of synapses present in these developmental phases.

See also Francis Crick: Neuroscience and other interests

References

External links

Crick; Mitchison, G (1995). "REM sleep and neural nets". Behavioural Brain Research. 69 (1–2): 147–55. doi:10.1016/0166-4328(95)00006-F. PMID 7546306. S2CID 4011228.

Worked examples

Example 1 — a first encounter with Reverse learning

Start with the simplest possible case. Write down what Reverse learning claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Reverse learning before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Reverse learning ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Reverse learning

In research: Reverse learning appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Reverse learning in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Reverse learning is common in secondary-school and first-year university syllabi. It links to neighbouring topics Sleep, so understanding it makes those chapters shorter.
In everyday life: Look for Reverse learning outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Reverse learning in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Reverse learning means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Reverse learning out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Reverse learning in simple terms?

Why does Reverse learning matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Reverse learning?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Reverse learning.