Difference in gamma-band phase synchronization during semantic processing of visually presented words from primary and secondary languages

The difference in cortical mechanisms underlying processing different languages has been of great interest. Exploration of local and global functional connections between neuronal activities originating from task-relevant areas can contribute to a more complete understanding on these processes. Semantic processing is known to involve frontal and parietal activities, and thus, functional connection between anterior-posterior regions is expected during semantic processing of visually presented words. The major purpose of this study is to investigate whether a substantial difference in gamma-band phase synchronization (GBPS) is observed during semantic processing of visually presented words from primary (Korean) and secondary (English) languages. Conventional ERP component and evoked gamma-band activity (eGBA) analyses were also performed. Word pairs with closely-related or unrelated meanings were presented to 14 Korean subjects so that N400 event-related potential (ERP) component was evoked. Other components, such as P1, N1, and late positive component, could also be identified. The N1 was shown to be larger for Korean. Response times and N400 latencies were significantly faster for Korean. eGBAs were significantly smaller in response to English at ~ 100 ms poststimulus, and latencies were considerably delayed. We verified significant GBPS from anterior-posterior electrode pairs, and substantial difference between the two languages emerged in the GBPS pattern during the 200-350 ms period where significant GPBS was observed from more electrode pairs for Korean. This finding indicates that differences in cortical activities due to language differences are more evident in inter-regional connectivity during semantic analysis than during other stages, such as orthographic processing.