A closer look at how bilingualism can help delay the onset of Alzheimer's disease.
…it delays the onset of Alzheimer’s disease
Sometimes it pays to be stupid. Let me explain. I recently became aware of an article in Neurology that concluded that bilingual individuals may have a delay in the onset of the symptoms of their Alzheimer’s disease for up to four or five years (more on the study results here). Well, since I didn’t have what it takes (especially a respectable GPA) to get into medical school when I graduated college, I spent my first two years of med school in Italy. While there, I noticed that many people did not speak the same language as I did. In fact, since the exams were all oral and in Italian, it behooved me to learn the language. So, now I count myself among the ranks of the bilingual and, as such, perhaps I am more resistant to Alzheimer pathology than those unfortunate smart people who got into medical school in the USA.
The reason bilingual people may not display the effects of the tangles and plaques until their disease is more advanced have to do with a concept called “cognitive reserve.” The older concept of “brain reserve” represented a passive model of describing how neural decline would not vary among individuals. There would be a threshold of neuronal or synaptic loss beyond which a disease state would become symptomatic. Therefore, in PD, a loss of a certain number of cells in the substantia nigra would result in clinically recognized Parkinson symptoms. In Alzheimer’s disease, when a limit of cholinergic neurons were lost, cognitive impairment would manifest.
However, a more active model of cognitive reserve postulates that brains can make adjustments and adaptations to an injury—whether it be degenerative, traumatic, or otherwise induced. Under this model, it is not just a fixed threshold that determines when symptoms occur, but rather the interaction between brain loss and compensatory mechanisms that determine the neurological effects. To summarize:
1. Brain Reserve: Individual differences in the brain itself allow some people to cope better than others with brain pathology. These differences can be quantitative, such as larger brain, more neurons, or more synapses.
2. Cognitive Reserve: Individual differences in how people process tasks allow some to cope better than others with brain pathology.
a. Neural Reserve: Inter-individual variability—perhaps in the form of differing efficiency, capacity, or flexibility—in the brain networks or cognitive paradigms that underlie task performance in the healthy brain.
b.Neural Compensation: Inter-individual variability in the ability to compensate for brain pathology's disruption of standard processingnetworks by using brain structures or networksnot normally used by individuals with intact brains. This compensation may help maintain or improve performance.
Therefore, people with a greater cognitive reserve will display less symptoms of a disease given the same amount of cerebral pathology. This theory is represented with this graph:
It has previously been shown that educational achievement and occupational status are factors that can positively affect your cognitive reserves. However, it had not been previously demonstrated that being bilingual would also afford an individual the type of cognitive reserve that may result in the delay in demonstrating the cognitive impairment at similar degrees of Alzheimer’s pathology.
“Bilingual” was defined as“having spent the majority oflife, at least from early adulthood, regularly using at least 2 languages.” Two groups of AD patients were compared: mono vs. bilingual individuals (about 100 in each group). There was a 5.1-year difference in the age of onset of Alzheimer’s symptoms. Educational level was actually higher in the monolingual group, and so could not account for this remarkable difference. One confusing part of the article reports that immigration status was not shown to be a significant factor, though 75% of the bilingual patients were immigrants whereas the monolingual group had only 25% immigrants. It is not reported whether cultural/genetic factors were investigated. Interestingly, the most common second language was Yiddish, then Polish, Italian, and Hungarian.
So, if you are a middle-aged practitioner, you may want to start getting your affairs in order a little sooner than your bilingual colleagues. As for me, arrivederci. A la prossima volta.