On Reading In The Brain
The nature-versus-nurture debate is an old one. It stands to reason that extremism on either side is likely to be misguided. The mind is not a blank slate. But nor are we born with fully intact cognitive, linguistic and social capacities. What we do, as individuals, and as members of society, depends on our make up. But it also depends on the landscapes where we find ourselves and the resources available. What is striking is the remarkable degree to which we — all living beings — make it so. We change the world around us through our own actions, and this in turn brings about changes in our own internal organization.
As a case in point, consider reading.
We now know that reading is only possible thanks to the existence of dedicated neural structures in the brain. This is supported by a remarkable convergence of data from psychology, medicine, and the experimental neurosciences, deploying a wide range of different methodologies (single cell recordings of epilepsy patients) and imaging techniques (PET, fMRI, EEG, MEG, etc). The upshot is that all readers, regardless of whether they are reading English, French, Chinese, Hebrew or Swahili — and regardless of whether they are reading on a computer display, an iPad, a movie screen, or from the page of a book — show identical patterns of neural activation.
This reading area of the brain — what Stanislas Dehaene calls "the brain's letterbox" (located on the edge of the left occipito-temporal fissure) in his excellent new book devoted to this topic — lights up for grammatical words in the reader's language, and does not light up for meaningless combinations of letters or for numerical strings. Moreover, it is known that damage to the structures necessary for this activation, or in supporting structures, brings about distinctive and reading-specific deficits.
What makes this remarkable — Dehaene speaks of the paradox of reading — is that reading is a cultural practice of recent invention. Whereas it is likely that human beings have been talking and singing for some 75,000 years (give or take 25,000 years), we are pretty certain that writing is at most a few thousand years old.
This means that these brain structures that are now dedicated to reading were not selected for that purpose. We don't have an innate reading faculty. And this means that if we want to understand why our brains are the way they are — why we are each built the way we are — we need to look to the environment, and, specifically, to culture. It is the existence of the technological practice of writing — a recently invented social practice — that has created reading-specific systems in the brain.
Dehaene would surely grant this; when it comes to reading, cultural invention has taken the lead. But he is also quick to insist that this is no fodder for "culture relativists" who think that there is "infinite adaptability of brain to culture." Dehaene advances what he calls the "neuronal recycling hypothesis," according to which cultural invention can reorganize the brain, but only, in effect, by recycling already existing structures; it can invade and take hold of neural systems that initially have quite different functions. Specifically, Dehaene's idea is that there is a "fringe of variability" tolerated by the otherwise genetically predetermined visual object recognition system; this gives the degrees of freedom needed for culture to grab hold and turn the visual cortex into, as he puts it, "a text comprehension system." As a result, far from culture being the agent that sculpts our brains, the brain is a prior constraint on what culture can hope to achieve.
Dehaene offers a detailed and by and large convincing exposition of these ideas and I recommend the book enthusiastically to readers regardless of background. But I am puzzled as to why he characterizes the neuronal recycling hypothesis as radical, as he does.
Consider: If one is in the business of inventing a script, one had better be sure that the symbols are visually discriminable. Reading is, after all, for most of us at least, an application of our ability to see. Reading, then, will depend on everything that seeing depends on, including, necessarily, the relevant neural systems. So the idea that we make use of brain areas dedicated to seeing when we read — that we recycle these systems — is about as radical as the idea that when we play baseball we recycle neural systems that make running, throwing and catching possible. Or consider: Humans don't have neural systems that have been adapted to support flying or travel under water. That we are able to fly, and travel under water (by submarine, say), must therefore be a reapplication and also an extension of other capacities that we already have.
The beauty of Dehaene's account is that it allows us to see how the brain constrains our cultural practices even as our cultural practices also shape the brain itself. As I said at the outset, what we can do depends not only on how we are built but also on where we find ourselves, on the environment, including the cultural, technological environment. But these latter do not vary independently, at least not when looked at over both cultural and evolutionary time scales. For how we are built depends on where we find ourselves, and the nature of our environments, cultural and otherwise, is shaped by what we do and have done. We do not stand over against the world around us. We are part of it.
It's no miracle that we can read; there is no paradox. Writing, after all, is a tool, and tools are designed by us to be used by us, that is, by creatures with just our bodies and capacities, and also with just our needs, interests and circumstances. Dehaene's idea that the invention of writing can be thought of as the discovery that the visual cortex is a text comprehension system notwithstanding, reading isn't something that happens in the brain. It is something our brains enable us to do, but only in a broader world- and culture-involving context.