Neuroscience: The Metaphor of Lethe and Mnemosyne

Legend claims that two rivers flowed in Hades: Lethe and Mnemosyne. Whoever drank from the first forgot their existence and whoever drank from the second remembered everything. This story evokes a really important function of our own brains.

Written and verified by the psychologist Valeria Sabater.

Last update: 07 June, 2023

Forgetting information is sometimes as or more important than remembering it. However, you probably often get frustrated because your brain has a tendency to blur data, experiences, and images and you can’t clearly retrieve them. Moreover, faces fade from your memory and you even have a hard time locating where you met certain people, where you left your keys, or the name of that hotel where you had such a good time.

We live in a world that conveys the idea that memory is a reflection of cognitive health. Indeed, it’s the classic executive function that you tend to exercise the most in school. You memorize to establish new information and learn and pass your exams. But, over time, some of that information fades and vanishes like smoke escaping up the chimney.

However, you tend to forget that this is due to a principle of brain efficiency. What you don’t use you eliminate. It’s a healthy process. In fact, it’s how your brain maintains its subtle neurological balance and takes care of your mental resources. After all, although it’s often claimed to be the case, your brain isn’t a computer. It’s an organ with limited capacities. Therefore, it needs to prioritize and save energy.

As a matter of fact, forgetting allows you to improve your life. This idea evokes a beautiful Greek legend that perfectly exemplifies the process of remembering and erasing.

The metaphor of Lethe and Mnemosyne

Greek mythology and also Plato’s book, Republic tells the story that, in Hades, there were two rivers: Lethe and Mnemosyne. The first caused forgetfulness and the second favored memory. In fact, some funerary inscriptions from the fourth century B.C. suggest that the dead drank from the Lethe River to forget their lives. Therefore, they were unable to remember their past existences when they were reincarnated.

Plato explained that, in Greece, there were groups that practiced a mystery religion. Its initiates were asked to drink from the Mnemosyne River to achieve supposed enlightenment. Remembering every detail of their present and past lives was perceived as a form of revelation. Yet, in reality, such an idea, if it could ever materialize, would drive us crazy.

Indeed, our brains aren’t prepared to store every piece of information, detail, image, word, or experience. What’s more, human beings and even animals need to forget in order to remember. We’re going to explain why.

Lethe, forgetting to develop better

The Greeks thought that the effect of drinking water from the Lethe lasted until early childhood. This would explain why we can’t remember being born or our first two or three years of life. But, in reality, a child doesn’t remember their first birthday due to a process that’s both fascinating and essential: brain neurogenesis.

Before birth and during the first months of life, babies produce a large number of neurons. Gradually, the first synapses appear and neuronal pruning takes place. In other words, synaptic connections are removed to shape a more specialized and efficient brain. In this process, memories are erased, but greater strength and cognitive agility are achieved.

Neuroscience claims that forgetting is an active mechanism that begins to function from a really early age.

Every species that has memory forgets

The Lethe and Mnemosyne metaphor suggests that every living thing that possesses memory must forget to survive. In fact, a study conducted by The Scripps Research Institute Florida (USA), claims that dopamine is essential for establishing memories and learning. It’s also vital for promoting forgetting.

This phenomenon appears in both humans and fruit flies (Drosophila melanogaster). Indeed, mammals, reptiles, birds, fish, insects, and even fungi possess the function of forgetting as one of their most basic mechanisms.

So much so, that figures such as the cognitive psychologist, Oliver Hardt, from McGill University in Montreal, Canada, claim that every organism, however simple it may be, must constantly delete information. Only by doing this can it better adapt to its environment.

Eliminate the artificial, remember the essential

Experts in forensic psychology know that a witness will rarely remember an event with absolute precision. These experiences substantiate the metaphor of Lethe and Mnemosyne. In other words, we have to forget certain data to remember (prioritize) others. As such, the fact that the human being lacks a photographic and exact memory fulfills an adaptive purpose that’s both logical and effective.

For example, think about the individual who’s suffered a robbery with assault. If they were to remember the color of the attacker’s shoelaces, the tear in their jeans, the sound their jacket made when they moved, or the angle of the sun reflecting off it, they’d be storing useless data in their brain.

Their brain only wants to retain the essential information of the experience to prepare itself for future situations. The rest is superfluous. It doesn’t help the individual to know what color the attacker’s hair was. They’re more interested in establishing the context in which the event occurred in order to be prepared to act next time.

People who drink from Mnemosyne (hyperthymesia)

Hyperthymetic syndrome defines a rare condition in which an individual is able to remember a good part of their life experiences in exceptional detail. It should be noted that incidences are extremely low among the population. But, in 2005, the University of California (USA) published a study describing the case of one particular woman.

We could say an individual with hyperthymesia has drunk from the waters of the Mnemosyne River. Their memory doesn’t respond to any mnemonic technique but is automatic and spontaneous. This may seem like an extraordinary gift, but it isn’t. In fact, those who demonstrate this particularity also exhibit certain characteristics similar to autism.

Moreover, these individuals frequently feel mentally exhausted. This hinders their cognitive performance. Remembering data, scenes, and experiences in an involuntary and constant way is something of a burden. These individuals aren’t geniuses nor do they exhibit a higher-than-average intelligence. Quite the contrary, in fact.

Memory facilitates our learning and adaptation to the environment. It’s thanks to our memories that we acquire experiences and update ourselves on a daily basis in terms of knowledge and wisdom. However, forgetting allows us to advance as a species by modeling more agile and efficient brains, capable of storing valuable information and eliminating that which isn’t particularly useful.

In the balance between the two, lies our cognitive success. It’s there that the secrets of our survival are hidden.