Visualizing the number of neurons in the brain

Or how to see big numbers

If I were to tell you that the human brain has 100 billion neurons, can you picture it in any meaningful way ?

The core problem seems to be the lack of mental machinery for visualizing large numbers; for instance, close your eyes and imagine 2 apples, easy enough right ? 3,4 apples ? 6 apples ? 8 apples ?

If you are like most people your mental buffer ( or visual sketchpad in neuroscience lingo ) starts loosing detail and cohesion around the 4th Apple and struggles around the 7th. 9 are usually not visualized correctly.

These are 8 though, not 9.

One trick you can use is to group them in a grid or other meaningful way (standardizing the shape and removing detail also helps), this is usually called chunking and works for all types of memories, for instance imagine now a group of apples as dots in a grid:

Chunking works by referencing a group as a unit, for instance here we are chunking sets of 6 apples, suddenly visualizing 24 apples is less difficult:

We will use this technique later; for now let’s go back to define the problem of visualizing the number of neurons in the brain.

How many, where ?

There are a number of estimates, I’ll settle on the currently accepted 85 Billion rather than on the popular 100 Billion. Importantly, these neurons are divided in a gross manner into 69 Billion in the cerebellum and 16 Billion in the cortex.

A first visualization thus would look like this:

Unfortunately our gross division leaves much to be desired since there are a a lot of critical important areas distributed in between and encompassing these 2 neuronal mega cities ( think about a popular town or neighbourhood en route to a mayor city ), but as a first pass it will do.

Note: Numbers without meaning mean nothing, and while a fascinating,important and critical part of neuroanatomy,evolution and life... function is not the focus here, grasping the size of the machinery is.

Seeing one Billion things.

So the unit of reference for neurons would seem to be in the millions to billions , like with our apples example we will need to somehow chunk it down to size, imagine that each of the following squares is a neuron:

Somewhere between the first and second set of neurons, we loose familiarity, there seems to be no evolutionary advantage yet to distinguish these many things.

By the 3rd set ( 10,000 Neurons), we start loosing the ability to notice them individually, did you notice the 35 th neuron firing ( in red ) ?

Visualizing one million neurons can be facilitated by associations with other phenomena, for instance 1 million seconds are roughly equal to 11 days, that is if you were to count to one and repeat that for the next 11 days without pause you will have counted one million times.

Visualizing 10 to a 100 Million neurons requires a leap in mental faith, frames of reference lose meaning unless you constantly remind yourself about the previous units…10 million seconds are roughly 4 months and 100 million a little over 3 years, you can also scan these images in succession to get a sense of scale.

And finally here we are with our 1 billion unit or chunk,hopefully by now it is no longer scary, it will still take you about 31 years to count all the little squares that stand for neurons though.

A layered affair…

We could easily go on till we reached our 85 Billion target, but before we do so, let’s upgrade our visualization in a couple of ways, the first one involves taking into consideration that neurons are not laid flat across the brain but rather they usually stack one on top of each other in layers, additionally this layering is not uniform, ranging from around 3 layers in the cerebellum to an average of 50 in the cortex, so a further division could look like this:

And superficial

Another thing to consider is that neurons are usually found on the outside layer of the brain ( although they are more dispersed in the cerebellum and other structures) , the rest is mostly cabling (axons) and support cells and structures (glial cells ,blood vessels, fluid etc,):

But Not Flat

Alas, neurons are not neatly laid out flat even if layered, to account for a limited surface ( the skull ) neurons are compressed,folded or crinkled into mountains (giri)and valleys (sulci) much as if you were stuffing a flat tissue paper into a 3 dimensional object:

All together now:

So we have a visual method for chunking big numbers along with some insights into where and how neurons on the brain are located, let’s now try to piece these parts together for a final set of visualizations, starting with the 85 Billion in 1 billion chunks:

Let’s now layer them :

Distribute them :

And compress them:

Conclusions:

A first step towards grasping the complexity of the human brain is coming to terms with the impressive number of neurons it posses, unfortunately there is no easy way to grasp the billions of neurons involved, strategies like chunking and building sets towards ever bigger numbers help in some way to visualize them.

Additonally, some insights into their distribution can help us derive function out of these observations; for instance, through these very rudimentary illustrations we can observe that the cerebellum packs the bulk of the neurons in the brain and that the cortex while many times bigger in superficial volume has a smaller number of neurons. We can also observe that they are more sparsely distributed in the cortex and layered at a significant higher rate. Whatever functional analysis will need to explain these distributions…

And lastly, I hope this short set of illustrations and musings help you visualize the number of neurons in the brain better !

Keno

About the Author :

Born Eugenio Noyola Leon (Keno) I am a Designer, Developer/programmer, Artist and Inventor, currently living in Mexico City, you can find me at: www.k3no.com