Bilingual Patients With Temporal Lobe Epilepsy Show Higher Network Organization

Bilingualism demonstrated neuroprotective effects in patients with left-sided temporal lobe epilepsy, potentially due to increased neural reserve and higher levels of white matter network organization despite neurologic disease, according to study findings published online in Neurology.

Growing evidence suggests that bilingualism can lead to neuroplasticity and affect neural efficiency, which could result in resistance to neurologic disease. It remains unknown whether bilingualism is relevant to brain health in patients with epilepsy.

Researchers at the University of California in San Diego conducted an observational cohort study in which they analyzed whether bilingualism improved whole-brain structural white matter network organization, providing resistance to neurologic disease among patients with temporal lobe epilepsy.

They recruited 81 healthy control individuals and 29 bilingual and 88 monolingual patients with temporal lobe epilepsy from 2 specialized epilepsy centers. These individuals all underwent diffusion-weighted magnetic resonance imaging (MRI) scans and neuropsychological testing.

Researchers analyzed whole-brain connectomes using diffusion tractography and graph theory. In particular, they studied network integration based on path length and specialization based on transitivity and compared results between the patients with temporal lobe epilepsy and the controls individuals.

Patients with left-sided temporal lobe epilepsy who were bilingual demonstrated higher network organization than those who were monolingual. According to neuropsychological testing results, bilingual patients with left-sided temporal lobe epilepsy demonstrated higher efficiency with frontal executive function performance compared with monolingual individuals with left-sided temporal lobe epilepsy.  

In contrast, bilingual healthy control individuals did not demonstrate increased network organization as seen in the bilingual individuals with left-sided temporal lobe epilepsy, indicating that the neuroprotective effects of bilingualism may only appear in cases where neurologic disease is present.

Researchers suggested that these findings may be due to neural reserve, or the increased number of neurons and synapses that result from consistent training of the brain to maintain 2 different languages at the same time. This requires increased executive function and neural efficiency to constantly switch between the languages, activating one while inhibiting the other.

“Higher structural network organization in bilingual individuals with LTLE [left-sided temporal lobe epilepsy] suggests a neuromodulatory effect of bilingualism on whole-brain connectivity in epilepsy, providing evidence for neural reserve,” the researchers noted. “This may reflect attenuation of or compensation for epilepsy-related dysfunction of the left hemisphere, potentially driven by increased efficiency of frontal-executive networks that mediate dual-language control…[highlighting] a potential role of bilingualism as a protective factor in epilepsy…,” they added.

Study limitations included small sample size for bilingual patients with temporal lobe epilepsy, the cross-sectional study design, the potential effects of brain maintenance due to genetics and lifestyle factors which may have influenced neurological results, and possible alteration of results using other atlases than the 2 that were used for graph theory analysis in this study.