The Method of Loci allows you to instantly memorize a list of anything. It is the method of choice for world champion mnemonists, as detailed in Joshua Foer’s Moonwalking with Einstein.

While the method is usually linked with the hippocampus (literally means ‘seahorse’ because it kind of looks like one), it should really be associated with the locus coeruleus (literally means ‘the blue spot’ because, well, that’s what it looks like).

The hippocampus is the center of long-term memory. It integrates memories from your vision, hearing, sense of touch and everything else and combines them into memories of events and complex concepts.

First, off let’s explain what the world’s greatest memory technique is about.

You take a familiar route (most people start off with their house/apartment) and place the information you want to remember at different locations (e.g. different rooms). It is important to make the mental images of the information absurd.

Take a simple grocery list with five items:

Butter

Milk

Bread

Fish

Cornflakes

Then take a route with at least five points:

Bedroom

Livingroom

Bathroom

Staircase

Hallway

And combine them with an absurd twist:

You wake up swimming in butter.

You drag yourself into the livingroom, where you are met with a flood of milk.

You head over to the bathroom, where you catch your spouse/roommate trying to flush a huge baguette down the drains.

You rush down the stairs, but encounter a school of salmon swimming up towards you.

You finally reach the hallway, but have to fight yourself through a barrier of cornflakes.

The reason why this information is so easily remembered is that you are exploiting two phenomenons: locations are already stored in your long-term memory (in the hippocampus) in sequence-form, and absurdity works like mental glue.

We all have familiar routes stored in memory. In fact, the hippocampus grows as you store more routes in them. London cab-drivers have to remember a ton of routes to pass their cab-exams. Because of this, their hippocampi are larger than in normal people.

The more points on your route, the more information you can store along it.

When I first heard of this technique I wanted to test it. I was taking an introductory psychology class with a single book on the curriculum. It was filled with dates and names. Memorizing all of them seemed pointless. But I wanted to see how far I could push this supposedly ‘amazing’ memory technique. It took me several hours, but I created a loci in my mind with around 300 points. Each point had a character, a date relating to the character, and a symbol of his or her achievements. Taking the exam I almost felt like I was cheating. I had a map of the history of psychology in my head. Everything was in chronological order. Tracing the developments in the field was as easy as daydreaming. Because that was what I was doing. I don’t want to say that I aced the exam. It would be more honest to say that the Method of Loci aced the exam.

Now you might be wondering when I’m going to talk about the locus coeruleus. That’s great, because I was just getting to it.

The locus coeruleus is located in a part of your brain (the pons) that is, evolutionary speaking, 505 million years old. You know how when you dream you don’t actually run around in real life? That’s all thanks to the pons. The need for the locus coeruleus is as old as the need not to act out your dreams. Which suggests that it popped up about when organisms started dreaming. Is that a coincidence? I think not. We’ll get back to this later.

It sends signals to your whole brain. Except for one spot. The basal ganglia. The reason why it will soon become obvious.

What exactly does the locus coeruleus do?

Like I said, it sends signals to your whole brain. I will include the name of the chemical it uses, noradrenaline, because there’s some funny to it. Everyone calls it noradrenaline, except for Americans. They used to call it noradrenaline, but a pharmaceutical company patented the name, so now they have to call it norepinephrine instead. That’s just so American.

The basic job of the locus coeruleus (blue spot) is to send a “Wait, what?” signal to the rest of the brain

As illustrated above, the locus coeruleus lets the brain know when something unexpected has occurred — It sends a “Wait, what?” signal.

You know all those routes memorized by the hippocampus? They are all thanks to the locus coeruleus.

In experiments with rats, it has been shown that interrupting the “Wait, what?” signal, by preventing the locus coeruleus from contacting the hippocampus with noradrenaline, eliminates their ability to memorize routes.

It turns out that the “Wait, what?” signal makes you stop what you’re doing because something’s not right. It also takes what you just experienced and stores it as a memory. Why? Probably because something weird just happened and now might not be the best time to get to the bottom of it.

This brings us to an interesting phenomenon. Researchers have discovered that when rats dream, they show the same brain activity that they showed when they were running through mazes earlier. They are using the “Wait, what?” moments from the day before to update their knowledge of the world. They have collected some pieces. They are using their dreams to find out where they fit in the larger puzzle: the mental maps of their minds.

When you dream, the locus coeruleus isn’t doing anything. But the basal ganglia, the only place in the brain not contacted by the locus coeruleus, is very active.

What does the basal ganglia do? It breaks down the complexity of your thoughts and behavior to manageable chunks; it optimizes your behavior by taking into account both cost and benefit. Simply put: it eliminates your wasteful output (and the opposite: it facilitates lucrative output). Habits and skills are products of the basal ganglia.

This is why the locus coeruleus isn’t contacting the basal ganglia. Your basal ganglia is optimizing the program you are running (‘making lunch’ for instance), while the locus coeruleus interrupts the program when something unexpected happens (like a knock on the door).

You might not have needed to know all this about the basal ganglia to understand the Method of Loci, but I think it’s always good to see the big picture of what’s going on.

Your mental route is created with the help of the locus coeruleus. When you create absurd images, your locus coeruleus is going “Wait, what?”, thus forming strong memories. The combination of the two gives you the most powerful memory technique there is.

In addition to understanding the Method of Loci better, I think we have also learned the reason why we dream. We dream so that we can update our knowledge of the world. We all have mental models of the world that can explain some fraction of what we experience. When we experience something we didn’t expect based on our model, we use dreams to incorporate this information into an updated version of the model.

So there you have it. How the world’s greatest memory technique works. And as an added bonus: the nature of dreams.