The neurobiology of forgetting. Why your brain throws knowledge away – and how to stop it

Mar 29

Written by NESSE

NESSE graphic: The neurobiology of forgetting. Why your brain throws knowledge away – and how to stop it

The maths of fading: Ebbinghaus’s legacy

It all began in 1885, when Hermann Ebbinghaus carried out pioneering research on memory. He was the first to describe the Forgetting Curve, showing that the process of losing information starts almost immediately after it is learned. The data are demanding, but consistent across later studies:

Within a few dozen minutes you lose more than half of what you learned.
After 24 hours, roughly one third of the information remains in your memory – if you do nothing with it.

For years people wondered whether these figures still hold in the age of modern education. In 2015, a research team led by Jaap Murre replicated Ebbinghaus’s experiments. The results (published in PLOS ONE) left no illusions: the forgetting curve is still exponential and is a stable feature of the human memory system – without active reinforcement, the amount of knowledge retained drops sharply over days and weeks. Estimates show that after about a month, retention can fall to just a few per cent of the original material.

This means that of an eight-hour workshop, only a small, fragmentary slice remains in your head – mostly general impressions and a few examples.

The 72-hour window: the synapses’ biological “deadline”

Why do we at NESSE place so much emphasis on the first three days after training? The answer lies in synaptic plasticity. Learning is a physical change in the structure of your brain – the creation and strengthening of connections between neurons.

After intensive learning, synapses enter a period of increased plasticity which – according to research on memory consolidation – can last up to about 72 hours. During this time consolidation takes place, i.e. the gradual stabilisation of new connections and the integration of memory traces into wider neural networks. At the molecular level, this involves, among other things, local protein synthesis in the synapses, which is necessary for a memory trace to have a chance of becoming relatively lasting.

If you don’t use the new knowledge in this critical time window, your brain starts treating some of the fresh connections as less important and gradually weakens them. From an evolutionary point of view, maintaining unused neural connections is too costly in terms of energy, so the brain “clears the disk” to make room for information that actually helps you solve everyday problems. So every new technique you don’t test in the first few days has a very high risk of being extinguished quickly – instead of becoming part of your behavioural repertoire.

Active recall: why reading your notes is a waste of time

Many training participants go back to the materials and “look through them” to refresh their memory. Research by Henry Roediger and Jeffrey Karpicke (2006) showed that this strategy – based on simply rereading – mainly gives a false sense of fluency, and poor long-term retention.

The real breakthrough is active recall . It involves effortfully retrieving information from memory without the help of sources – notes, slides or prompts.

The experiment: Roediger and Karpicke compared two groups. The first read a text several times (reread); the second read it once and then repeatedly recalled it from memory by answering questions (test).
The result: After a week, the group using the testing strategy (active recall) achieved clearly higher scores in the final test than the group that reread the text several times – the differences were of the order of several dozen percentage points in favour of active recall, depending on the conditions of the experiment.

Forcing the brain to make the effort of recalling information strengthens neural pathways in the hippocampus and prefrontal cortex, the key structures responsible for memory and cognitive control. It’s a signal to your nervous system: “This information takes effort to retrieve, so it’s important – it’s worth consolidating for longer.”

Interleaving: how to learn for real business

Most of us learn in blocks (so-called blocked practice) – e.g. we spend a whole day just learning how to close a sale. Although this gives a sense of rapid progress, research shows that this form of training often loses out to other methods when it comes to how lasting it is and how well skills transfer to real work.

The solution is interleaving . It involves mixing the new skill with old tasks or other competencies – e.g. you alternate practising closing a sale with conversations about customer needs, work on a proposal and a follow-up email. Meta-analyses and more recent studies show that interleaving can significantly improve problem-solving and the transfer of knowledge to new situations.

Why does it work? Interleaving forces the brain to keep switching between contexts and to recognise which tool is right at a given moment, instead of “reeling off” one pattern.

The effect: Although it may subjectively feel as if you’re doing worse while learning (because it’s harder), long-term retention is usually higher than with blocked learning. In practice, this better reflects real office conditions, where problems don’t come in neat blocks but require quickly juggling different competencies.

Summary: your strategy for making knowledge survive

Learning isn’t only an intellectual process – above all it’s a biological one. For your training to make sense, you need to:

Beat the forgetting curveby going back to the material (even briefly) within the first day after the training.
Make use of the window of roughly the first 72 hours for a first practical test of the new skill – even in a small, safe situation.
Use active recall, i.e. regularly ask yourself “what do I remember from this and how would I apply it?”, instead of just leafing through slides.
Interleave tasks, weaving the new knowledge into your daily routine, instead of keeping it in a “training drawer”.

Then biology stops being your enemy and starts working in your favour.