Originally published on Scientific American MIND’s Guest Blog on August 22, 2016.
After prepping for the day’s cases, “Mike Brennan,” a 63-year-old cardiology technician, sat down for his morning coffee and paper. On the front page, he discovered something troubling: he could no longer read. No matter how long he stared at a word, its meaning was lost on him.
With a history of smoking and hypertension, he worried that he might have had a stroke. So, leaving his coffee, he walked himself down the hall to the emergency department, where neurologists performed a battery of tests to tease out what had happened.
Mike still recognized individual letters and, with great difficulty, could sound out small words. But even some simple vocabulary presented problems, for example, he read “desk” as “dish” or “flame” as “thame.” Function words such as prepositions and pronouns gave him particular trouble.
Mike couldn’t read, but there was nothing wrong with his eyes. Words heard were no problem. He could recognize colors, faces, and objects. He could speak, move, think and even write normally. Mike had “pure alexia,” meaning he could not read but showed no other impairments.
An M.R.I. scan of Mike’s brain revealed a pea-sized stroke in his left inferior occipitotemporal cortex, a region on the brain’s surface just behind the left ear.
Mike’s doctors called in neurologist Peter Turkeltaub, director of Georgetown University’s Cognitive Recovery Laboratory, who recognized this was the first case of such a small stroke causing pure alexia. “Pure alexia is a classic neurological syndrome that has been described for well over 100 years,” Turkeltaub wrote me. He had seen many patients with the condition in his career. But, he noted, “This particular case was unusual only because the alexia was caused by a very small stroke,” and the damage was in a location linked to a decades-old debate surrounding the neuroscience of language.
The Case for the Visual Word Form Area
Mike was not my patient, but his stroke, which occurred in 2010, was of such significance to our understanding of how the brain processes the written word that I was determined to track down the details of his case.
Studies in the early 1990s had identified activity in the left inferior occipitotemporal cortex—the area damaged in Mike’s stroke—when someone saw letters that spelled out meaningful words. Thus scientists wondered whether the region was involved in recognizing words and letters from the contrast lines and curves detected by the eye. They called this location the “visual word form area.”
These early findings were exciting, puzzling, and contentious—the kind that, at a conference, provokes shouts and screams from otherwise calm and collected scientists. Such studies were also very new, recalled neuroscientist Peter T. Fox, a pioneer of such research on language. As a result, many other researchers were dubious of the work as a whole. “I remember getting grants rejected with comments like ‘central brain activation can teach us nothing about language—nothing, it has no role in language studies’,” Fox said.
Neuroscientists have two approaches for assessing the role of a particular brain area. Lesion-deficit studies were first performed by ancient Roman physicians, who noticed that damage to regions of the brain caused specific behavioral deficits (e.g. a gladiator gets hit on the right side of their head—the lesion—and loses the ability to move his left arm—the deficit). Activation studies using neuroimaging work the other way: you record where the brain is active while performing a particular task, like reading. (In this sense, Mike’s story, involving both damage and imaging, sits at the intersection of the classical and the modern.)
Each method has its strengths and weaknesses. “Activation studies show that a particular brain region is engaged during a task, but it doesn’t show that it’s a necessary and sufficient condition for that task,” Fox explained. “And yet, because the brain has redundant wiring, it’s nearly impossible to claim that a stroke in a particular area, like the visual word form area, is necessary and sufficient to eliminate a particular function.” So even though multiple activation studies reported the visual word form area existed, the behavioral neurologists weren’t convinced.
And there were several reasons to think such an area was “a myth,” as one skeptical 2003 paper put it. For one thing, the very search for a “visual word form area” was misguided because it personified the brain’s real work, which is to process and decode visual information. Brain regions act as an assembly line of neural groups that each contribute some cognitive rivet or weld to a larger percept. A visual word form area confused an assembly line for a one-man-band.
Finally there was the problem of evolution. Because reading was a relatively new cultural invention, humans couldn’t have evolved to read text in the same way that mammals evolved to recognize faces—there simply hadn’t been enough time. This made it hard to believe in a brain structure expressly devoted to reading.
A decade before Mike’s stroke, Turkeltaub had shown that a child’s brain shifts where and how it processes text as he or she learns to read. But because children are also learning to walk, talk, write, and otherwise be human, it was hard to say what brain changes were caused by literacy alone. It took a series of studies with adults learning to read for the first time, to nail down the truth about the visual word form area.
An Unlikely Opportunity
At the turn of the 21st century, a large group of Colombian guerrillas abandoned their weapons and, after decades of fighting, rejoined mainstream society. Without formal education, many of the fighters learned to read for the first time as 20-somethings.
Camouflaged within this Colombian drama, a group of neuroscientists led by Manuel Carrerias, Scientific Director of Spain’s Basque Center on Cognition, Brain and Language, saw an opportunity to study how learning to read changes the adult brain. Working with Catherine Price, a neuroscientist at University College London, Carrerias used M.R.I. to track changes in the brain as the former guerrillas learned to read. They discovered that learning to read was associated with enlarged grey matter in specific brain areas and further that brain activity within these regions became more tightly coordinated with improved literacy, showing that structural and functional changes occurred simultaneously. Much as high commuter traffic promotes asphalting and widening of thoroughfares to improve traffic flow, brain activity associated with learning how to read promotes the strengthening of specific neural highways, allowing specialized neural centers to more efficiently perform the cognitive task of reading.
Carrerias and Price’s findings, published in 2009, fleshed out the brain’s reading networks but didn’t find any evidence supporting the role of a visual word form area. The next major advance in the case for the visual word form area came from Stanislas Dehaene, a neuroscientist at the French Institute of Health and Medical Research. In 2010 Dehaene proposed that reading networks build on evolutionarily older functions at the expense of those functions. To test his hypothesis, Dehaene gathered illiterate adults, people who learned to read in adulthood, and literate adults schooled in childhood.
Comparing these groups, Dehaene reported that the more literate a person was, the less responsive the visual word form area became towards other visual stimuli—in particular to faces—and more focused it became towards writing. In poor readers, meanwhile, the visual word form area responded relatively indiscriminately to words, faces, shapes, and checkerboards. As Dehaene predicted, when one learns to read, the left inferior occipitotemporal cortex is recycled from a general visual recognition center to a specialized word recognition center, at the expense of other tasks.
Mike’s stroke served as the final piece of the puzzle: a case of pure alexia caused by damage in only the visual word form area. As with most scientific knowledge, the exact role of the visual word form area is still unresolved. However, it is no longer a myth. And the way in which the area is repurposed from general visual recognition to word specialist is a reminder of how powerfully the brain can retool and adapt—essential processes both in learning and healing.
Thanks to that brain plasticity, Mike recovered quickly. Guided by Whitney Postman, a speech language therapist and an assistant professor at St. Louis University whose post-doctoral work at the NIH focused on post-stroke aphasia, Mike began tailored therapy to help him overcome his difficulty with function words. She fashioned a “brute force approach” in which he viewed, copied, said, and spelled lists of vocabulary in various contexts. “It’s pretty much the way we learn to use these function words as children,” Postman said.
For his part, Mike was a highly motivated pupil. He and Postman had only two sessions. One month after his stroke, his letter-by-letter reading was greatly improved. After three months, he was reading patient charts and lab values at work—and his morning paper.