Authors :
Presenting Author: Alena Stasenko, PhD – UCSD
Erik Kaestner, PhD – UCSD
Adam Schadler, MS – UCSD
Clare Urbanic, BS – UCSD
Anny Reyes, PhD – Cleveland Clinic
Giselle Carollo-Duprey, PhD – UCLA
Daniel Saldana, PhD – MGH/Harvard
Christopher Benjamin, PhD – UCSD
Monika Polczynska, PhD – UCLA
Lucia Cavanagh, PhD – UCLA
Carrie McDonald, PhD – UCSD
Rationale: Bilingualism has been associated with more bilateral language lateralization compared to monolingualism, suggestive of increased neuroplasticity. It is less known how a developmental insult like epilepsy modulates this effect and what factors determine the extent of neuroplasticity of the first (L1) versus second (L2) acquired language networks. Our previous findings suggested increased bilingualism-related neuroplasticity of L2 in the presence of left (but not right) hemisphere seizures. In a larger and independent cohort that completed fMRI language mapping in both languages we aimed to determine: 1) the effect of seizure laterality on language lateralization in L1 and L2, and 2) how this effect interacts with bilingual factors (e.g., proficiency and age of L2 acquisition).
Methods: Twenty-four bilingual and 46 monolingual adults with temporal lobe epilepsy (TLE) completed three fMRI lexical-semantic naming tasks, which bilingual patients completed in L1 and L2. A conjunction map was generated based on the overlap of activation present across all three tasks. The dependent variable was a laterality index based on activations in the left versus right hemisphere.
Results: For L1, bilinguals showed more bilateral activation than monolinguals (
p=.04), which did not interact with seizure laterality (i.e., left versus right TLE). For L2, bilinguals showed more bilateral activation than monolinguals, but only in left TLE (i.e., a significant interaction;
p=.03;
ηp2=.07). Within the bilingual group, whereas L1 lateralization did not vary by seizure laterality, L2 showed more bilateral lateralization in left versus right TLE (
p=0.02), an interaction of a large effect (
p=.04;
ηp2=.18). In a subset of 9 bilinguals with left TLE, a closer proximity between the age of seizure onset and age of L2 acquisition was correlated with more bilateral lateralization (
rho=0.73,
p=.03). Higher L2 proficiency was associated with greater bilateral language representation (
rho= -.51;
p=.04). Finally, language status (i.e., bi-versus monolingual) was a more robust predictor of language lateralization than age of seizure onset, seizure laterality, and handedness.
Conclusions: Bilingualism may result in more bilateral language lateralization, particularly for L2 in the presence of left hemisphere seizures. In addition to seizure laterality, the timing of seizure onset relative to language acquisition appears important for explaining the extent of neuroplasticity. That is, when seizures develop in the language-dominant hemisphere, an adaptive compensatory process might be triggered in the right hemisphere, especially while L2 networks are still developing. These data underscore the importance of considering individual bilingual language factors during pre-surgical planning and evaluating patients in both languages to accurately access risk for post-operative decline. Our findings are consistent with observations from the bilingual stroke and dementia literature showing distinct patterns of L1 vs L2 function and suggest potentially distinct trajectories of L1 versus L2 recovery following epilepsy surgery, warranting further investigation.
Funding: NIH
R01NS124585;
F32NS119285; K01NS124831