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Bilingualism and cognitive recovery after stroke

by on 2015/12/04

In the past few years, there’s been increasing interest in understanding how knowing more than one language might protect our thinking skills against the ageing process. We reported on one of those studies a couple of years ago, “Can learning a second language delay dementia?”, and new research from the same team suggests that knowing more than one language may also aid recovery after a stroke. The findings were widely reported, for example on BBC News “Bilingual skills enhance stroke recovery, study finds”, and in the Telegraph “Bilingual people twice as likely to recover from a stroke”. So, let’s take a closer look at the research behind those headlines.

What did the researchers actually do?

The new study, published in the journal Stroke, comes from a team of researchers based in Hyderabad, India, and Cambridge and Edinburgh in the UK. Hyderabad provides an excellent area to study the effects of bilingualism on different outcomes, as many people speak more than one language, but there is less confounding of this with immigration status.

The researchers reviewed patients admitted for stroke between 2006-13, who completed assessments of cognitive function and whether they had dementia between 3 and 24 months after their stroke. Participants were also rated on their bilingualism status, which the researchers defined as “the ability to communicate in 2 or more languages in interaction with other speakers of these same languages”. In total, 608 people who had been admitted for a stroke were included in the study; just over 30% developed a form of dementia linked to stroke and about one quarter were said to be cognitively impaired (where scores on some of their thinking tests were lower than would be predicted for their age and educational level, but not so impaired to be diagnosed with dementia). About 30% of the participants were rated as being ‘cognitively normal’, that is, when assessed after their stroke their cognitive functions did not seem to be lower than would be expected.

The proportion of those in these different outcome groups were then compared in the bilinguals versus monolinguals. The findings suggested that 40.5% of the bilinguals were rated as cognitively normal after stroke, versus only 19.6% of the monolinguals. Conversely, cognitive impairment or dementia was present in 77.7% of the monolinguals versus 49.0% of the bilinguals. In short, the bilinguals were doing better, at least in terms of their cognitive function status, between 3 and 24 months after having had a stroke. In further analysis, the researchers suggested the protective effect of bilingualism remained even after accounting for other known risk factors, including age and hypertension, for example.

As this is the first study examining the associations between bilingualism and stroke recovery, there’s still a lot more that needs to be explored to fully understand what it is that might account for the protective effect. However, the researchers suggested that in this population at least, there were no differences in the presence of the other risk factors (for example, hypertension or smoking history) before stroke in the bilingual versus monolinguals, “suggesting that the observed differences are not because of a healthier lifestyle among bilinguals”. As a tentative suggestion for what might account for bilingualism’s protective effects, the researchers suggest it might not be purely about language per se, but rather a lifetime of switching between languages which involves higher-order “executive functions”.

What did the media say?

While the first part of the Daily Mail’s headline is a shade misleading “Being bilingual ‘beats strokes’”, as all those in the study had had a stroke, the remainder was actually very informative, reading:“40% of people who speak multiple languages recover full mental functions compared to 20% who only speak one“. It’s rare to see such detailed figures in a headline, and rarer still to see them so carefully worded.

Indeed the piece itself gives a brief but clear overview of the study, including a quote from one of the study co-authors, Thomas Bak from the University of Edinburgh: “Bilingualism makes people switch from one language to another, so while they inhibit one language, they have to activate another to communicate. This switching offers practically constant brain training which may be a factor in helping stroke patients recover.”

The media reports cited above were equally clear in their coverage, and perhaps one of the only issues to raise would be the sense of recovery from stroke being suggested as a single entity. The current study looked at the cognitive aspects of stroke recovery, but, for many people, there are also physical impairments immediately post-stroke, that recover to varying extents over the subsequent months. It may be that bilingualism affects this physical recovery too via some neurological mechanism, and we’d certainly be interested in knowing that. For now though, it’s clearer to focus on the results of the study that assessed cognitive status, and indeed, the second part of the Daily Mail headline did just that.

The bottom line.

The results from this new study are interesting, and add to a growing body of literature on the potentially protective effects of knowing more than one language. As carefully pointed out, it is the first study to look at this, meaning that we need other researchers to examine the same things in different samples to confirm the findings. It’s also important to remember that the current study was observational, so it can’t make causal inferences. While a number of factors were accounted for, it’s still possible that bilingualism is a marker for some other factor or group of factors, and it’s these other things that account for the protective effect (of course, studying the lifetime accrued effect of bilingualism isn’t something we can easily do in a fully controlled trial!). The question for many might also be, would learning a language in midlife or old age reduce the risk of stroke, or aid post-stroke recovery? On that, I’m sure there’ll be more to come…

Alladi, S. et al. (2016). Impact of Bilingualism on Cognitive Outcome After Stroke. Stroke. DOI: 10.1161/STROKEAHA.115.010418

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