Cortical Dynamics of Semantic Processing during Sentence Comprehension: Evidence from Event-Related Optical Signals

Jian Huang,Shiwei Jia,Hsuan-Chih Chen,Deyuan Mo,Suiping Wang,Vincent M Reid

doi:10.1371/journal.pone.0070671

Abstract

Using the event-related optical signal (EROS) technique, this study investigated the dynamics of semantic brain activation during sentence comprehension. Participants read sentences constituent-by-constituent and made a semantic judgment at the end of each sentence. The EROSs were recorded simultaneously with ERPs and time-locked to expected or unexpected sentence-final target words. The unexpected words evoked a larger N400 and a late positivity than the expected ones. Critically, the EROS results revealed activations first in the left posterior middle temporal gyrus (LpMTG) between 128 and 192 ms, then in the left anterior inferior frontal gyrus (LaIFG), the left middle frontal gyrus (LMFG), and the LpMTG in the N400 time window, and finally in the left posterior inferior frontal gyrus (LpIFG) between 832 and 864 ms. Also, expected words elicited greater activation than unexpected words in the left anterior temporal lobe (LATL) between 192 and 256 ms. These results suggest that the early lexical-semantic retrieval reflected by the LpMTG activation is followed by two different semantic integration processes: a relatively rapid and transient integration in the LATL and a relatively slow but enduring integration in the LaIFG/LMFG and the LpMTG. The late activation in the LpIFG, however, may reflect cognitive control.

Highlights

Semantic processing during sentence comprehension involves retrieving the meanings of individual words and integrating those meanings into a larger semantic unit [1±4]
Previous fMRI studies have frequently shown that the left inferior frontal gyrus (LIFG) plays a significant role in semantic integration [4,13,15], other imaging studies on auditory language comprehension [17±19] have revealed that the anterior temporal lobe (ATL), especially the left anterior temporal lobe (LATL), is recruited during semantic integration
event-related optical signal (EROS) Results As shown in Table 2 and Figure 4, the left posterior middle temporal gyrus (LpMTG) activation that occurred between 128 and 192 ms was significantly larger in the unexpected condition than in the expected condition

Summary

Introduction

Semantic processing during sentence comprehension involves retrieving the meanings of individual words and integrating those meanings into a larger semantic unit [1±4]. There is no consistent evidence for the exact time point at which lexical-semantic retrieval and semantic integration occur in sentence processing. A large number of studies have consistently shown that various semantic variables could affect a relatively late ERP component, i.e. N400, which leads to the well-known conclusion that semantic processing occurs in the N400 time window typically between 300 to 500ms [12±15]. Studies using techniques with high spatial resolution such as PET and fMRI have consistently shown that the left posterior middle temporal gyrus (LpMTG) is engaged in lexical-semantic retrieval [14,15,16]. The roles of the LIFG and the LATL in semantic integration during language comprehension have not yet been conclusively determined

Results

Discussion

Conclusion