“A larger proportion of bilinguals had normal cognition compared with monolinguals (40.5% versus 19.6%; P<0.0001), whereas the reverse was noted in patients with cognitive impairment, including vascular dementia and vascular mild cognitive impairment (monolinguals 77.7% versus bilinguals 49.0%; P<0.0009). There were no differences in the frequency of aphasia (monolinguals 11.8% versus bilinguals 10.5%; P=0.354). Bilingualism was found to be an independent predictor of poststroke cognitive impairment."
Impact of Bilingualism on Cognitive Outcome After Stroke.
Alladi S, Bak TH, Mekala S, Rajan A, Chaudhuri JR, Mioshi E, Krovvidi R, Surampudi B, Duggirala V, Kaul S.Stroke. 2016 Jan;47(1):258-61. doi: 10.1161/STROKEAHA.115.010418. Epub 2015 Nov 19.