Identifying cortical first and second language sites via navigated transcranial magnetic stimulation of the left hemisphere in bilinguals

- rTMS induces naming errors in both languages in the left hemisphere of bilinguals.
- The first (L1) and second language (L2) are partially processed by different cortical areas.
- The distribution of L1 is more stable than that of the language acquired later (L2).

The cortical areas that code for the first (L1) and second language (L2) in bilinguals have still not been sufficiently explored. Thus, this study investigated the left-hemispheric distribution of the L1 and L2 using repetitive navigated transcranial magnetic stimulation (rTMS), in combination with an object-naming task, in 10 healthy, right-handed volunteers.In particular, higher error rates (ERs) were observed in the L1, and there was a statistically significant difference between the ERs of L1 and L2 for no-response errors (L1 mean 11.9 ± 9.0%, L2 mean 6.5 ± 5.2%; p = 0.03). Furthermore, language-specific and shared cortical distribution patterns for the L1 and L2 were observed within the frontal, parietal, and temporal lobes with a trend towards higher occurrence of language-specific spots within posterior regions. Overall, the L1 presented a more stable pattern of language distribution compared to the L2.