After a stroke, many people face communication challenges. Stroke's impact on language and speech can be significant and difficult. Some people have trouble speaking. Some have difficulty understanding words spoken by others. Reading, writing and math skills may also be affected.
In neurological diseases such as stroke, spelling — a core language skill — is commonly affected.
Spelling a word involves the retrieval of information about the word's letters and their order from long-term memory as well as the maintenance and processing of this information by working memory in preparation for serial production by the motor system.
With long-term memory difficulties, people can't remember how to spell words they once knew and tend to make educated guesses. With working memory issues, people know how to spell words but they have trouble choosing the correct letters.
They could probably correctly guess a predictably spelled word like "camp," but with a more unpredictable spelling like "sauce," they might try "soss." In severe cases, people trying to spell "lion" might offer things like "lonp," "lint" and even "tiger."
Now, neuroscientists have pinpointed the parts of the brain that control how we write words and link basic spelling difficulties for the first time with damage to seemingly unrelated regions of the brain, shedding new light on the mechanics of language and memory. The researchers studied 15 years' worth of cases in which 33 people were left with spelling impairments after suffering strokes. Some of the people had long-term memory difficulties, others working-memory issues.
According to lead author Brenda Rapp, a professor in the Department of Cognitive Sciences at Johns Hopkins University in Baltimore, when something goes wrong with spelling, it is not just one thing that happens in the brain. Different things can happen, and they come from different breakdowns in the brain's machinery. So, depending on what part breaks, a person will have different symptoms.
To examine these issues, researchers in this study used a voxel-based mapping approach to analyze the lesion distribution of 27 individuals with dysgraphia subsequent to stroke — who were identified on the basis of their behavioral profiles alone, as suffering from deficits only affecting either orthographic long-term or working memory — as well as six other individuals with deficits affecting both sets of processes.
The findings provide, for the first time, clear evidence of substrates that selectively support orthographic long-term and working memory processes, with orthographic long-term memory deficits centered in either the left posterior inferior frontal region or left ventral temporal cortex, and orthographic working memory deficits primarily arising from lesions of the left parietal cortex centered on the intraparietal sulcus.
In working memory cases, the lesions were primarily also in the left hemisphere but in a different area — in the upper part of the brain toward the back. The researchers were surprised at how distant and distinct the brain regions are that support these two subcomponents of the writing process, especially two subcomponents that are so closely inter-related during spelling. According Rapp, the areas have been thought to be closer together and harder to tease apart.
These findings also contribute to understanding the relationship between the neural instantiation of written language processes and spoken language, working memory and other cognitive skills. The researchers believe the findings could lead to improved behavioral treatments after brain damage and more effective ways to teach spelling.
