The Neuroscience of Reading: Using Research to Understand Reading Acquisition and Disorders

This summer I was lucky enough to attend the week-long Learning and the Brain conference entitled “The Neuroscience of Reading: Using Research to Understand Reading Acquisition and Disorders” at Boston University. I am so glad I went! I have long been interested in the science of the reading brain and fascinated by the remarkable feat that is reading, or as neuroscientist Dr. John Gabrieli put it during the first lecture, “language made visible.” It continues to amaze me that our brains are wired for speech but not print yet somehow our brains can develop the neural pathways necessary for reading.

We covered a lot over the course of the week, but I’ve synthesized the information I found most interesting below, and at some point, I’d love to find a way to share this with my colleagues:

There are three neural pathways for reading: two slower, analytic ones, the parieto-temporal and frontal, that are used mainly by beginning readers, for slowly sounding out words, and an express route, the occipito-temporal, relied on by experienced, skilled readers. Skilled readers activate highly interconnected neural systems that encompass regions in the back and front of the left side of the brain. Beginning readers must first analyze a word; skilled readers identify a word instantaneously. The parieto-temporal system works for the novice reader: slow and analytic, its function seems to be in the early stages of learning to read, that is, in initially analyzing a word, pulling it apart, and linking its letters to their sounds. In contrast, the occipito-temporal region is the express pathway to reading and is the one used by skilled readers. The more skilled the reader, the more they activate this region. It responds very rapidly (faster than a heartbeat) to seeing a word; instead of analyzing a word, the occipito-temporal area reacts almost instantaneously to the whole word as a pattern. One brief glance and the word is automatically identified on sight. The occipito-temporal region is referred to as the word form area or system.

After a child has analyzed and correctly read a word several times, they form an exact neural model of that specific word; the model (word form), reflecting the words spelling, its pronunciation, and its meaning, is now permanently stored in the occipito-temporal system. Subsequently, just seeing the word in print immediately activates the word form area and all the relevant information about that word. It all happens automatically, without conscious thought or effort. Readers shift from reliance on the temporoparietal region to the visual word form region, consistent with a shift from effortful phonological decoding to automatic word recognition as reading proficiency increases. As skilled readers speed through the text, the word form area is in full gear, instantly recognizing one word after another. There is a strong link between reading skill and reliance on the word form area.

The early learning of letters is as much a spatial problem as it is a language problem. The left hemisphere processes language and the right hemisphere is where visual spatial information is processed. There's a shift from right-hemisphere to left-hemisphere brain pathways for reading as children grow older. The right hemisphere is involved in early reading when the brain is focused on the spatial decoding of letters but once a child becomes a fluent reader they jump directly from print to meaning and it's no longer visual-spatial but a direct path to language and meaning. This early reliance on the right hemisphere explains why letter reversals are so common in beginning readers/writers: to recognize objects in the world, it’s helpful to generalize over left/right percepts, i.e., being able to recognize a tiger (or any threat) whether its left or right side is facing you is important; however, this generalization is not helpful for recognizing letters (e.g., letters such as b/d p/q.) Letter reversals are NOT an indicator of dyslexia. A chair is a chair no matter what, and children see letters the same way.

Units of written language vary across languages: alphabetic languages are ones where graphemes correspond to phonemes; regular languages approach one to one mapping. This is called orthographical transparency–how much a single letter or group of letters represents a single sound. Italian and Spanish are highly transparent, with nearly a 1:1 ratio of graphemes to phonemes, that is if you see how a word is spelled you know how to say it aloud. For example, in Italian, the ratio is 33 to 25 meaning there are 33 ways to write 25 sounds and children can become skilled readers in one year. English has poor transparency because it's full of exceptions (such as the silent s in island) with an average of nearly 30 alternative pronunciations for each grapheme. By contrast, English has 44 phonemes (sounds) but hundreds of ways to represent these sounds in writing: Consider the long u sound, which can be made in multiple ways: u (unicorn); u_e (cube); ou (you); eau (beauty); iew (view); eu (feud); yu (yule); ew (few); eue (queue)! Not surprisingly, it can take children 3 years to become skilled readers of English.

Dyslexia often arises from impaired phonological awareness which is the auditory analysis of spoken language that relates the sounds of language to print, or the auditory processing of the sounds of language. 5 to 17% of children have developmental dyslexia which is a persistent difficulty in learning to read that is not explained by sensory deficits, cognitive deficits, lack of motivation or lack of adequate reading instruction. Outside of school in fifth grade a good reader may read as many words in 2 days as a poor reader does in an entire year. Dyslexia is persistent: a student who fails to read adequately in first grade has a 90% probability of reading poorly in fourth grade and a 75% probability of reading poorly in high school.It’s characterized by difficulties in accurate and/or fluent word recognition and by poor spelling and decoding abilities; deficit in the phonological component of language; unexpected in relation to other cognitive abilities and the provision of effective classroom instruction; secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge; you need to be able to exclude cultural, educational, environmental, or other disabilities in order to diagnose it. The language itself drives the difficulties themselves. For example, in Spanish-speaking kids with dyslexia will likely have an easier time with spelling b/c language is phonetic but more challenges with fluent reading. The best predictors of future reading difficulty in pre-readers are challenges with phonological awareness w/ spoken language, rapid naming, and letter knowledge. Newborns from families with versus without familial risk for dyslexia exhibit differences in ERP responses to language sounds within hours or days of birth. (ERP stands for event-related potential and measures the brain’s electrical activity in response to a specific sensory, cognitive or motor event.) ERP responses to speech sounds within 36 hours of birth discriminated with over 81% accuracy those infants who would go on to become dyslexic readers at age 8. These studies indicate that brain differences are present near the time of birth that greatly enhance the risk for and underscore the developmental nature of dyslexia