English-speaking and bilingual Mexican Americans make a better recovery from strokes than their counterparts who speak Spanish alone, according to a new study. Whether the improved outcomes reflect changes language makes to the brain, or if other differences in the samples were responsible, remains uncertain. However, the findings raise the possibility that the way languages shape our brain could be much more important than is usually acknowledged.

A month ago, the most powerful evidence yet was published for the influence of native languages on brain development. A comparison of native German and Arabic speakers found greater connections between the two hemispheres for Arabic speakers. Meanwhile, those who speak German apparently have more developed language networks in their left hemispheres. It is thought the differences reflect the contrast in the demands the two tongues place on the brain.

That study didn’t investigate whether such differences affect capacities beyond those needed for the languages themselves. However, work now published in a new paper suggests the impact may be real and substantial, at least for those unfortunate enough to suffer a stroke at some point in their life.

Previous studies have found the consequences of stroke are worse for Mexican Americans than non-Hispanic white Americans. There are many possible explanations for this, ranging from genetic factors to unequal medical treatment. Dr Lewis Morgenstern of the University of Michigan in Ann Arbor sought to test the possibility that language is a contributing factor.

Morgenstern and co-authors studied the recoveries of 1,096 Mexican Americans in Corpus Christi, Texas, taking out some of the other potential influences. All those in the study were tested three months after the stroke. The authors compared their results in three areas: neurologic – covering aspects such as muscle strength, speech, and coordination – thinking and memory skills, and ability to perform daily tasks. Testing was done by certified bilingual staff.

“Our study found that Mexican American people who spoke only Spanish had worse neurologic outcomes three months after having a stroke than Mexican American people who spoke only English or were bilingual,” Morgenstern said in a statement. There were no significant differences on the other two measures, but the neurologic gap was substantial. The Spanish speakers had an average score of seven on a 44-point scale for stroke affectedness, while English and bilingual speakers averaged four.

Even though the population chosen for the study is relatively homogenous, the sample groups were not identical. Spanish-only speakers were older and less educated than those who spoke English. On the other hand, they were less likely to smoke. After the authors controlled for these differences the gap in neurologic recovery shrank to 1.9 points, but remained significant. 

The authors acknowledge a larger sample of Spanish-only speakers would improve confidence in the conclusions. There could also be some unidentified difference, such as income, between the groups they were not controlled for – this is certainly not a topic that can be tested by randomized controlled trials.

“We conducted an earlier study in this same community finding that the language people spoke was not associated with any delay in their getting to the hospital or using emergency medical services after an ischemic stroke, so we definitely need more information to determine what is driving the differences in outcomes between these two groups,” Morgenstern said.

Spanish and English are more similar to each other than Arabic and German, so if the difference really does relate to language-induced brain changes there is potential for even larger variation among those with other native tongues. 

The study is published in Neurology.