Scientists find area in brain that is prewired for reading

From MIT News:

Neuroscientists have long wondered why the brain has a region exclusively dedicated to reading — a skill that is unique to humans and only developed about 5,400 years ago.

Study finds brain connections key to reading

Pathways that exist before kids learn to read may determine development of brain’s word recognition area.

Anne Trafton | MIT News Office
August 8, 2016

A new study from MIT reveals that a brain region dedicated to reading has connections for that skill even before children learn to read.

By scanning the brains of children before and after they learned to read, the researchers found that they could predict the precise location where each child’s visual word form area (VWFA) would develop, based on the connections of that region to other parts of the brain.

Neuroscientists have long wondered why the brain has a region exclusively dedicated to reading — a skill that is unique to humans and only developed about 5,400 years ago, which is not enough time for evolution to have reshaped the brain for that specific task. The new study suggests that the VWFA, located in an area that receives visual input, has pre-existing connections to brain regions associated with language processing, making it ideally suited to become devoted to reading.

“Long-range connections that allow this region to talk to other areas of the brain seem to drive function,” says Zeynep Saygin, a postdoc at MIT’s McGovern Institute for Brain Research. “As far as we can tell, within this larger fusiform region of the brain, only the reading area has these particular sets of connections, and that’s how it’s distinguished from adjacent cortex.”

Saygin is the lead author of the study, which appears in the Aug. 8 issue of Nature Neuroscience. Nancy Kanwisher, the Walter A. Rosenblith Professor of Brain and Cognitive Sciences and a member of the McGovern Institute, is the paper’s senior author.

Specialized for reading

The brain’s cortex, where most cognitive functions occur, has areas specialized for reading as well as face recognition, language comprehension, and many other tasks. Neuroscientists have hypothesized that the locations of these functions may be determined by prewired connections to other parts of the brain, but they have had few good opportunities to test this hypothesis.

Reading presents a unique opportunity to study this question because it is not learned right away, giving scientists a chance to examine the brain region that will become the VWFA before children know how to read. This region, located in the fusiform gyrus, at the base of the brain, is responsible for recognizing strings of letters.

Children participating in the study were scanned twice — at 5 years of age, before learning to read, and at 8 years, after they learned to read. In the scans at age 8, the researchers precisely defined the VWFA for each child by using functional magnetic resonance imaging (fMRI) to measure brain activity as the children read. They also used a technique called diffusion-weighted imaging to trace the connections between the VWFA and other parts of the brain.

The researchers saw no indication from fMRI scans that the VWFA was responding to words at age 5. However, the region that would become the VWFA was already different from adjacent cortex in its connectivity patterns. These patterns were so distinctive that they could be used to accurately predict the precise location where each child’s VWFA would later develop.

Although the area that will become the VWFA does not respond preferentially to letters at age 5, Saygin says it is likely that the region is involved in some kind of high-level object recognition before it gets taken over for word recognition as a child learns to read. Still unknown is how and why the brain forms those connections early in life.

Pre-existing connections

Kanwisher and Saygin have found that the VWFA is connected to language regions of the brain in adults, but the new findings in children offer strong evidence that those connections exist before reading is learned, and are not the result of learning to read, according to Stanislas Dehaene, a professor and the chair of experimental cognitive psychology at the College de France, who wrote a commentary on the paper for Nature Neuroscience.

“To genuinely test the hypothesis that the VWFA owes its specialization to a pre-existing connectivity pattern, it was necessary to measure brain connectivity in children before they learned to read,” wrote Dehaene, who was not involved in the study. “Although many children, at the age of 5, did not have a VWFA yet, the connections that were already in place could be used to anticipate where the VWFA would appear once they learned to read.”

The MIT team now plans to study whether this kind of brain imaging could help identify children who are at risk of developing dyslexia and other reading difficulties.

Read more.

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Visual word form area in visual cortex remembers words as pictures

From Georgetown University Medical School Press Release:

After Learning New Words, Brain Sees Them as Pictures

WASHINGTON (March 24, 2015) — When we look at a known word, our brain sees it like a picture, not a group of letters needing to be processed. That’s the finding from a Georgetown University Medical Center (GUMC) study published in the Journal of Neuroscience, which shows the brain learns words quickly by tuning neurons to respond to a complete word, not parts of it.

Neurons respond differently to real words, such as turf, than to nonsense words, such as turt, showing that a small area of the brain is “holistically tuned” to recognize complete words, says the study’s senior author, Maximilian Riesenhuber, PhD, who leads the GUMC Laboratory for Computational Cognitive Neuroscience.

“We are not recognizing words by quickly spelling them out or identifying parts of words, as some researchers have suggested. Instead, neurons in a small brain area remember how the whole word looks — using what could be called a visual dictionary,” he says.

This small area in the brain, called the visual word form area, is found in the left side of the visual cortex, opposite from the fusiform face area on the right side, which remembers how faces look. “One area is selective for a whole face, allowing us to quickly recognize people, and the other is selective for a whole word, which helps us read quickly,” Riesenhuber says.

The study asked 25 adult participants to learn a set of 150 nonsense words. The brain plasticity associated with learning was investigated with functional magnetic resonance imaging (fMRI), both before and after training.

Using a specific fMRI technique know as fMRI-rapid adaptation, the investigators found that the visual word form area changed as the participants learned the nonsense words.  Before training the neurons responded like the training words were nonsense words, but after training the neurons responded to the learned words like they were real words.  “This study is the first of its kind to show how neurons change their tuning with learning words, demonstrating the brain’s plasticity,“ says the study’s lead author, Laurie Glezer, PhD.

The findings not only help reveal how the brain processes words, but also provides insights into how to help people with reading disabilities, says Riesenhuber. “For people who cannot learn words by phonetically spelling them out — which is the usual method for teaching reading — learning the whole word as a visual object may be a good strategy.”

In fact, after the team’s first groundbreaking study on the visual dictionary was published in Neuron in 2009, Riesenhuber says they were contacted by a number of people who had experienced reading difficulties and teachers helping people with reading difficulties, reporting that learning word as visual objects helped a great deal.  That study revealed the existence of a neural representation for whole written real words — also known as an orthographic lexicon —the current study now shows how novel words can become incorporated after learning in this lexicon.

“The visual word form area does not care how the word sounds, just how the letters of the word look together,” he says. “The fact that this kind of learning only happens in one very small part of the brain is a nice example of selective plasticity in the brain,”

Read more.