Neuronal recycling – now we’re getting somewhere. How in the world do our brains adapt to the recent invention of writing and therefore what naturally follows: reading? In chapter 3 of Reading in the brain: the new science of how we read, author Stanislas Dehaene puts forth a new term called “neuronal recycling” to explain how the brain learns to read.
Neuronal Recycling – Takeaway #1
Our brains have evolved over millions of years. For the vast majority of people, we are born with the natural ability to speak and listen. Writing only emerged just over 5,000 years ago and reading followed. Why was writing invented? Civilizations wanted an answer to the question of how to communicate our language through vision? Writing emerged as a visual representation of our spoken words.
In a quick 5,000 years, the brain did not have enough time to evolve naturally so it made the most of what it had to work with: enter the world of neuronal recycling. Neuronal recycling is the ability for the brain’s letterbox to learn and become a reading device. (The blogs from chapter 2 are all about the brain’s letterbox: The Brain’s Amazing Letterbox and The Brain’s Letterbox – More Top 10 Moments from Chapter 2.)
Our writing systems then adapted to match what the brain’s letterbox could naturally do. Stanislas Dehaene calls this feat “neuronal recycling” and this is the focus of chapter 3 in his book.
Neuronal Recycling – Takeaway #2
What do we learn? It is not efficient for a baby to learn to breath, see, chew, suck, or hear so those needs are hard-wired into the brain. However, babies are very sensitive to the 3D contours of faces (not flat ovals). The plasticity of a baby’s brain allows it to learn each facet of a parent’s face: front, side, other side, partial side view, bottom-up front angle, etc…
When the baby sees the same object (mom, for example) over and over in succession across time from those different angles, these visual neurons are coded to link all those different vantage points to the same object: mom. “This means that one neuron ends up responding to two [or more] entirely different images [viewpoints] whose only shared property is their occurrence in close temporal succession.” (Dehaene, 2010, p. 143)
In 1949, Donald Hebb, a Canadian neurophysiologist, coined the phrase “neurons that fire together, wire together”. This is how a baby knows its mother’s face regardless of lighting, angle, distance, position, size, or location. (Dehaene, 2010, p. 125)
Neuronal Recycling – Takeaway #3
So where does neuronal recycling come in? Hang tight. We’re getting there.
The idea that our eyes and brain can map a face from the millions of pixels that it sees into one image of our mom is phenomenal efficiency. The retina “explodes incoming images into a million pixels” and jigsaws them back together in a neuronal pyramid of steps. (Dehaene, 2010, p. 130) At the most basic level, millions of neurons are working in tandem to view the image. The neurons have to work together because a single neuron for each image is not efficient and consumes too much space in our brains.
Each of those million neurons represents a fragment of the image being seen: a straight line up, a curve down to the left, a curve up to the right, a straight line on top, a contoured curve angling up towards a line, etc… When all of these million fragments come back together like a jigsaw puzzle, we see an image. If the image is seen over and over again successively, then the combined set of neurons map to that visual representation (i.e. mom’s face).
Our brain does this mapping with a “gigantic array of simple parallel processors”. (Dehaene, 2010, p. 132) A simple parallel processor divides a complex task over multiple processors to compute more quickly. This can be compared to what happens when you try a new food. Sight, smell, taste, and texture are all processed simultaneously to quickly give you a food experience and an opinion of whether or not you liked it.
This simple parallel processing idea is exactly how the post office machine reads and sorts addresses and envelopes. Through a lightning fast error correction feedback loop, the machines reads typed words, printed words, and cursive to determine if what it sees is a straight line up, a curve down to the left, a curve up to the right, a straight line on top, etc… — just how a baby maps neurons together to recognize its mom. Oh, and this is also how facial recognition software works as well. It maps the contours, curves, shapes, lines, and depth of our face to open our phones…. (Whoa.)
Neuronal Recycling – Takeaway #4
Are we getting back to neuronal recycling, Lisa? Almost there.
What is culture? Culture is what binds us together as a group. It is a “shared set of mental representations that define a given group of human beings.” (Dehaene, 2010, p. 148) Writing, and then reading, has sustained and expanded our culture across thousands of years as we attempt to push our spoken words into a visual representation: print.
“We recognize the written word using a region that has evolved [over the past 10 million years] and whose speciality is the visual identification of objects.” (Dehaene, 2010, p. 125) Evolution takes too long so the brain efficiently reuses its natural brain circuitry to push the writing and reading system forward more quickly. The letterbox area’s circuitry has enough plasticity to adapt to learn to read through “neuronal recycling”, a term coined by Dehaene. (Dehaene, 2010, p. 144)
Dehaene chooses the word “recycle” with intention. In his native language of French, “se recycler” means to retrain (for a new job) or to take a refresher course (to obtain updated information for a current job). In Dehaene’s words, neuronal recycling “transforms an ancient function … into a novel function that is more useful in the present cultural context.” (Dehaene, 2010, p. 147)
Neuronal Recycling – Takeaway #5
Neuronal recycling is the workaround for our brain’s natural circuitry. By definition, recycling should be fast and short-term. Glass recycling takes approximately 30 days – quick, efficient, and helpful for our environment. Neuronal recycling should also be quick and efficient for our brain as well as useful for our culture.
The process to recycle glass is not a free-for-all. The process is limited because you can’t turn recycled glass into just any item because of the limits placed on its physical properties. Glass is more suited to be recycled into some objects more than others because of the quickness, efficiency, and usefulness of the recycled object.
The same is true for neuronal recycling. The range of how we recycle the neurons from the brain’s letterbox is restricted to its circuitry. We cannot limitlessly perform neuronal recycling but we can work with the neural pathways inside the letterbox.
Neuronal Recycling – Final Thoughts
All of the millions of billions of neurons in our brain have to work together to be the most efficient at everything. Neuronal recycling takes this evolutionary network of circuits and repurposes parts of it to learn to read.
Writing and reading, two cultural inventions, are “useful to humans and stable enough to proliferate from brain to brain”. (Dehaene, 2010, p. 147) Brain circuitry is similar across all languages and geographical locations. The brain’s letterbox (which performs the neuronal recycling) is located in the same area of each person across the globe.
In my opinion, a cultural disruption of the inventions is happening right now. It is not a neuronal recycling disruption of our how our brains learn to read but rather a disruption of whose brain’s circuitry is learning to read.
Enter the right to read, various human rights commissions, and new reading laws being implemented across the country. The vast body neuroscience research on how the brain learns to read has been around for decades. Who is learning to read and who is not is quite unchanged in decades.
This blog does not completely summarize the key points in chapter 3 of Dehaene’s book Reading in the brain: the new science of how we read. Therefore, like what happened in the chapter 2 blogs, there will be a P.S., a post script, an “oh, and also” for chapter 3. In particular, I will explain how neuronal recycling takes place in the letterbox.
In this series of blogs, I unpack my interpretations of Dehaene’s book about how we learn to read. The blogs in this series are:
- #1: “Introduction: 3 Important Wow Moments”
- #2: “Chapter 1 (Part 1): Amazing Ideas”
- #3: “Chapter 1 (Part 2): 4 Big Considerations”
- #4: “Chapter 2: the Brain’s Amazing Letterbox”
- #5: “Chapter 2: 10 More Memorable Moments”
Find video versions of these blogs on my YouTube channel: L’Essentiel French Resources. Keep moving forward with me for more chapters of this super-interesting book. My name is Lisa with L’Essentiel French Resources.
Resources:
– Dehaene, S. (2021). How we learn: Why brains learn better than any machine…for now. Penguin Books..
– Dehaene, S. (2010). Reading in the brain: The new science of how we read. Penguin Books. (I receive a commission if you purchase either Dehaene book from Amazon.)
