![]() How can this view explain why all readers possess a specialized and reproducibly located area for a recent cultural invention? The idea is that the act of reading is tightly constrained by the preexisting brain architectures for language and vision. Each cultural object must find its neuronal niche-a set of circuits that are sufficiently close to the required function and sufficiently plastic to be partially “recycled.” The theory stipulates that cultural inventions always involve the recycling of older cerebral structures that originally were selected by evolution to address very different problems but manage, more or less successfully, to shift toward a novel cultural use. On the contrary, new cultural inventions such as writing are only possible inasmuch as they fit within our preexisting brain architecture. 5 We should stop thinking of human culture as a distinctly social layer, free to vary without bounds, independent of our biological endowment. According to a theoretical proposal called the neuronal recycling hypothesis, which I introduced with colleague Laurent Cohen a few years ago, the human brain contains highly organized cortical maps that constrain subsequent learning. Resolving this paradox requires thinking about the state of the brain prior to literacy. How is it, then, that we all possess a specialized letterbox area? Reading as Neuronal Recycling Thus, there was no time for Darwinian evolution to shape our genome and adapt our brain networks to the particularities of reading. But how is this possible, given that reading is an extremely recent and highly variable cultural activity? The alphabet is only about 4,000 years old, and until recently, only a very small fraction of humanity could read. The brain of any educated adult contains a circuit specialized for reading. Yet many of these patients can still speak and understand spoken language fluently, and they may even still write only their visual capacity to process letter strings seems dramatically affected. He or she will be unable to recognize even a single word, as well as faces, objects, digits, and Arabic numerals. Furthermore, if it is impaired or disconnected via brain surgery or a cerebral infarct (type of stroke), the patient may develop a syndrome called pure alexia. For instance, the letterbox is the first visual area that recognizes that “READ” and “read” depict the same word by representing strings of letters invariantly for changes in case, which is no small feat if you consider that uppercase and lowercase letters such as “A” and “a” bear very little similarity. Yet it performs highly sophisticated operations that are indispensable to fluent reading. 4 Its efficiency is so great that it even responds to words that we fail to recognize consciously-words made subliminal by flashing them for a fraction of a second. The letterbox responds to written words more than it does to most other categories of visual stimuli, including pictures of faces, objects, houses, and even Arabic numerals. Indeed, this site is amazingly specialized. And, if it is destroyed or disconnected, as in the patient whose brain scan is shown at right, we may selectively lose the capacity to read.Įxperts call this region the visual word form area, but in a recent book for the general public, 3 I dubbed it the “brain’s letterbox,” because it concentrates much of our visual knowledge of letters and their configurations. In all of us, it is systematically located at the same place within a “mosaic” of ventral preferences for various categories of objects. It shows a stronger activation to words than to many other categories of visual stimuli, such as pictures of objects, faces, or places. 2 Figure 1. The visual word form area-the brain’s letterbox-is a small region of the human visual system that systematically activates whenever we read. Written words never fail to activate a small region at the base of the left hemisphere, always at the same place, give or take a few millimeters. A brief localizer scan, during which images of brain activity are collected as a person responds to written words, faces, objects, and other visual stimuli, serves to identify this region. 1 In particular, a small region of the visual cortex becomes active with remarkable reproducibility in the brains of all readers (see figure 1). Whenever we read-whether our language is Japanese, Hebrew, English, or Italian-each of us relies on very similar brain networks. Although I find the diversity of the world’s writing systems bewildering, there is a striking regularity that remains hidden.
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