A new study has revealed why stroke impairs reading, showing survivors lose the ability to use word meanings to recognise words on the page – a finding that may offer new therapeutic approaches.
Researchers found that people who have experienced strokes struggle with reading because they can no longer map the words they are trying to pronounce back to the ideas behind them.
While reading difficulties after stroke have long been observed, the precise mechanism behind this problem had not been fully understood.
The study, led by researchers at Georgetown University, analysed brain scans from 56 people who had left-hemisphere strokes and 68 without strokes while they read aloud.
They found that damage to the superior temporal sulcus – a brain region important for speech processing and short-term memory of sounds – prevented survivors from using word meaning to support reading.
This area and its connections affect how people link words they are pronouncing back to the ideas behind them.
The researchers also identified an overlapping brain region related to impairments in connecting meanings of words to their sounds, or phonology.
Peter E. Turkeltaub, MD, PhD is director of the Cognitive Recovery Lab at Georgetown University and senior author of the study.
He said: “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 recognise it when reading.”
Some people recovering from stroke can’t use the meanings of words to help recognise them, making it harder to read.
The researchers tested this by comparing how well participants read words with high imageability (easily pictured words such as ‘hammer’ or ‘cow’) with words of low imageability (abstract ideas such as ‘justice’ that are harder to visualise).
The study focused on left-hemisphere strokes, as this side of the brain is responsible for language processing.
Processing word meanings was found to be less common and milder than phonological impairment – difficulty sounding out words – which affects most stroke patients.
Phonology refers to the sound system of language.
Co-first author Ryan Staples, PhD, a postdoctoral fellow in Turkeltaub’s lab, said: “Our findings clarify the neurobiology of reading and provide the strongest evidence to date for a form of reading disorder that can occur after a left hemisphere stroke.”
