Abstract
In the present study we investigate the communication of different large scale brain sites during an overt language production task with state of the art methods for the estimation of EEG functional connectivity. Participants performed a semantic blocking task in which objects were named in semantically homogeneous blocks of trials consisting of members of a semantic category (e.g., all objects are tools) or in heterogeneous blocks, consisting of unrelated objects. The classic pattern of slower naming times in the homogeneous relative to heterogeneous blocks is assumed to reflect the duration of lexical selection. For the collected data in the homogeneous and heterogeneous conditions the imaginary part of coherency (ImC) was evaluated at different frequencies. The ImC is a measure for detecting the coupling of different brain sites acting on sensor level. Most importantly, the ImC is robust to the artifact of volume conduction. We analyzed the ImC at all pairs of 56 EEG channels across all frequencies. Contrasting the two experimental conditions we found pronounced differences in the theta band at 7 Hz and estimated the most dominant underlying brain sources via a minimum norm inverse solution based on the ImC. As a result of the source localization, we observed connectivity between occipito-temporal and frontal areas, which are well-known to play a major role in lexical-semantic language processes. Our findings demonstrate the feasibility of investigating interactive brain activity during overt language production.
Highlights
Electroencephalographic measures have long played only a minor role in the investigation of language production
In the present study we investigate the communication of different large scale brain sites during an overt language production task with state of the art methods for the estimation of EEG functional connectivity
In the blocking paradigm participants name objects that are presented in blocks of trials that consist of a homogeneous group of category members or blocks that consist of semantically unrelated objects
Summary
Electroencephalographic measures have long played only a minor role in the investigation of language production. Semantic context effects in classic speech production paradigms such as the picture-wordinterference (PWI) paradigm (Hirschfeld et al, 2008), the semantic blocking paradigm (Aristei et al, 2011, see Maess et al, 2002 for evidence from magnetoencephalography) or the cumulative semantic interference paradigm (Costa et al, 2009) have been shown to elicit modulations in the event-related brain potential (ERP) within a latency range of well-below 300 ms post-stimulus onset. When the pictures are repeatedly named (but typically not when they are named for the first time), a semantic interference effect is observed that reflects slower naming times in the homogeneous relative to the heterogeneous condition. Aristei et al (2011) reported ERPs elicited by semantic contexts around 200 ms after stimulus onset at occipito-temporal and frontal scalp regions (see Costa et al, 2009 for similar findings)
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