Health Scan: Blind people use the same brain region as sighted people when reading words in Braille.
By JUDY SIEGEL-ITZKOVICH
The part of the brain responsible for visual reading doesn’t require vision at all, according to a new study by researchers from the Hebrew University of Jerusalem and France. Brain imaging studies of blind people as they read words in Braille show activity in exactly the same brain region that lights up when sighted people read. The researchers said their findings challenge the textbook notion that the brain is divided into regions that are specialized for processing information coming in via one sense or another.“The brain is not a sensory machine, although it often looks like one; it is a task machine,” explained HU brain scientist and research team leader Dr. Amir Amedi, whose work on the topic is reported in the latest issue of Current Biology. “A particular area fulfills a unique function, in this case reading, regardless of sensory input modality,”he said. Amedi is affiliated with the university’s Institute for Medical Research Israel-Canada and the Edmond and Lily Safra Center for Brain Sciences.Unlike other tasks the brain performs, reading is a recent invention – only about 5,400 years old, and Braille has been in use for less than two centuries. “That’s not enough time for evolution to have shaped a brain module for reading,” Amedi said.Nevertheless, brain scans have shown that a very specific part of the brain known as the Visual Word Form Area (VWFA) – first discovered in sighted people by co-author Dr. Laurent Cohen of Paris – has been coopted for this purpose. But no one knew what might happen in the brains of blind people who learn to read despite the fact that they’ve had no visual experience.In the new study, Amedi’s team, which included doctoral student Lior Reich, used functional magnetic resonance imaging (fMRI) to measure the neural activity in eight people who had been blind since birth while they read Braille words or nonsense Braille. If the brain were organized around processing sensory information, one might expect that Braille reading would depend on regions dedicated to processing tactile information, Amedi explained. If instead the brain is task-oriented, you’d expect to find the peak of activity across the entire brain in the VWFA, right where it occurs in sighted readers – and that is what the researchers saw.Further comparison of brain activity in the blind and sighted readers showed that the patterns in the VWFA were indistinguishable between the two.“The main functional properties of the VWFA as identified in sighted are present as well in the blind, and are thus independent of the sensory-modality of reading and even more surprisingly do not require any visual experience,”the researchers wrote. “To the best of our judgment, this provides the strongest support so far for the metamodal theory of brain function,” which suggests that brain regions are defined by the computations they perform. The researchers suggest that the VWFA is a multisensory integration area that binds simple features into more elaborate shape descriptions, making it ideal for the relatively new task of reading. Amedi said he and his research team will study brain activity in people while they learn to read Braille to find out how rapidly this takeover happens. “What we want to find out is how does the brain change to process information in words and is it instantaneous.”HEARING AFFECTS DEMENTIA Older people who suffer from hearing loss are significantly more likely to develop dementia over time than those who retain their hearing, according to a study by Johns Hopkins University School of Medicine and US National Institute on Aging researchers. The findings could lead to new ways to combat dementia – a condition that affects millions of people worldwide, the scientists said.Although the reason for the link between the two conditions is unknown, the investigators suggest that a common pathology may underlie both, or that the strain of decoding sounds over the years may overwhelm the brains of people with hearing loss, leaving them more vulnerable to dementia. They also speculate that hearing loss could lead to dementia by making individuals more socially isolated – a known risk factor for cognitive disorders. Whatever the cause, the scientists report, their finding may offer a starting point for interventions – even as simple as hearing aids – that could delay or prevent dementia.
“Researchers have looked at what affects hearing loss, but few have looked at how hearing loss affects cognitive brain function,” said study leader Prof. Frank Lin of the otology division at Johns Hopkins.“There hasn’t been much crosstalk between otologists and geriatricians, so it’s been unclear whether hearing loss and dementia are related.”To make the connection, Lin and his colleagues used data from the Baltimore Longitudinal Study on Aging, launched 52 years ago by the national institute and which has tracked various health factors in thousands of men and women over decades.The new study, published in the February Archives of Neurology, included 639 people whose hearing and cognitive abilities were tested between 1990 and 1994. While about a quarter of the volunteers had some hearing loss at the start of the study, none had dementia. These volunteers were then closely followed with repeat examinations every one to two years, and by 2008, 58 of them had developed dementia.The researchers found that study participants with hearing loss at the beginning of the study were much more likely to develop dementia by the end.Compared with volunteers who had normal hearing, those with mild, moderate, and severe hearing loss had twofold, threefold, and fivefold risk of developing dementia over time. Even after the researchers took into account other factors that are associated with risk of dementia, including diabetes, high blood pressure, age, sex and race, Lin explains, hearing loss and dementia were still strongly connected.“A lot of people ignore hearing loss because it’s such a slow and insidious process,” Lin said.“Even if people feel as if they are not affected, we’re showing that it may well be a more serious problem.”