WASHINGTON – A key discovery about the impact of stroke on a person's ability to read reveals why a deficit occurs – a finding that presents a possible opportunity for new therapeutic strategies to help people recover one of the most important life skills.
It's long been known that people who experience a stroke can struggle with reading, but researchers weren't clear exactly why. Now, a new study, led by researchers at Georgetown University, reveals that strokes can rob a person's ability to use the meaning of words to help them recognize the words when reading.
"We usually think of reading in our daily lives as a way to gain meaning, but the opposite is also true: we rely on a word's meanings to help us recognize it when reading," says Peter E. Turkeltaub, MD, PhD, director of the Cognitive Recovery Lab at Georgetown University and senior author of the study. "Some people recovering from stroke can't use the meanings of words to help recognize them, making it harder to read."
It's long been known that people who experience a stroke can struggle with reading, but researchers weren't clear exactly why. So, the scientists looked at scanned images of brains damaged by stroke while study participants read aloud. The researchers were then able to pinpoint a part of the brain and related connections that affect how deciphering the meanings of words facilitates reading.
The National Institutes of Health (NIH)-funded study appears August 13 in the journal Brain.
In their study, the researchers found that the reason some stroke survivors can't use meanings of words to read is because they can't map the words they are trying to pronounce back to the ideas behind the words.
Annually, about 800,000 people in the U.S. have strokes, which disproportionately affect marginalized and minoritized people. In this study of 56 left-hemisphere stroke survivors and 68 people who had not had a stroke, processing the meaning of words was much less common and milder than phonological impairment, or the ability to sound out words, which is typical of most stroke patients. The study examined individuals with strokes on the left side of the brain because that is where language processing is located.
The researchers used imageability as a marker of how rich the meaning of a word was, and tested if success at reading words aloud related to their imageability. High imageability words can be easily pictured, such as 'hammer' or 'cow'. Low imageability words are hard to picture: 'justice' may evoke an image of the statue of Lady Justice holding balance scales, but the concept of justice can't really be pictured.
To better understand the impact of imageability, the researchers mapped the extent of the strokes with MRI imaging. The images revealed that damage along the superior temporal sulcus, a brain region that plays a crucial role in speech processing and auditory short-term memory, reduced the advantage of being able to read high imageability over low imageability words, reflecting an inability to use meaning to support reading. They also found an overlapping brain region that was related to impairments in connecting meanings of words to their sounds, or phonology. Together, these results demonstrate that some reading deficits occur in left-hemisphere stroke survivors as a result of an impaired integration of meaning and phonology.
"Our findings clarify the neurobiology of reading and provide the strongest evidence to date for a form of reading disorders that can occur after a left hemisphere stroke," says the study's co-first author Ryan Staples, Ph.D., a postdoctoral fellow in Turkeltaub's lab.
For their next steps, a recent 5-year grant from the NIH to study reading in normal aging compared to people who have had a left-hemisphere stroke should further enhance the understanding of the impact of strokes.
