Simultaneous Processing of Noun Cue and to-be-Produced Verb in Verb Generation Task: Electromagnetic Evidence

Abstract

A long-standing but implicit assumption is that words strongly associated with a presented cue are automatically activated in the memory through rapid spread of activation within brain semantic networks. The current study was aimed to provide direct evidence of such rapid access to words’ semantic representations and to investigate its neural sources using magnetoencephalography (MEG) and distributed source localization technique. Thirty-three neurotypical subjects underwent the MEG recording during verb generation task, which was to produce verbs related to the presented noun cues. Brain responses evoked by the noun cues were examined while manipulating the strength of association between the noun and the potential verb responses. The strong vs. weak noun-verb association led to a greater noun-related neural response at 250–400 ms after cue onset, and faster verb production. The cortical sources of the differential response were localized in left temporal pole, previously implicated in semantic access, and left ventrolateral prefrontal cortex (VLPFC), thought to subserve controlled semantic retrieval. The strength of the left VLPFC’s response to the nouns with strong verb associates was positively correlated to the speed of verbs production. Our findings empirically validate the theoretical expectation that in case of a strongly connected noun-verb pair, successful access to target verb representation may occur already at the stage of lexico-semantic analysis of the presented noun. Moreover, the MEG results suggest that contrary to the previous conclusion derived from fMRI studies left VLPFC supports selection of the target verb representations, even if they were retrieved from semantic memory rapidly and effortlessly. The discordance between MEG and fMRI findings in verb generation task may stem from different modes of neural activation captured by phase-locked activity in MEG and slow changes of blood-oxygen-level-dependent (BOLD) signal in fMRI.

Effortful verb retrieval from semantic memory drives beta suppression in mesial frontal regions involved in action initiation

“…Such motor reactivation may be redundant for verbs strongly associated with their nouns. In this case, a noun-elicited activation propagates across the strong links of preformed purely linguistic associative network, and is sufficient for retrieving the intended verb almost synchronously with semantic processing of the presented noun (Butorina et al, 2017). When noun-verb association is weak, a failure of automatic verb retrieval triggers additional activation of shared motor representations that may play a supportive role in the selection of the weakly associated verbs from semantic memory.…”

“…The nouns were selected using an independent norming study (for details, see Butorina et al, 2017). The nouns were selected using an independent norming study (for details, see Butorina et al, 2017).…”

“…The stimuli list comprised 65 Russian nouns with a single strong verb associate and 60 nouns that were weakly associated with many verbs (see a list of nouns in Supplementary Appendix S1). The nouns were selected using an independent norming study (for details, see Butorina et al, 2017). If the majority of the norming sample (from 58 to 90%) responded with the same verb to a presented noun, the noun was included into the Strong Association (SA) category (e.g., "soloveypoyet/nightingale-sings").…”

Efforful verb recollection drives beta suppression in mesial frontal regions involved in action initiation

“…Specifically, the beta ERD in higher-order motor areas of frontal cortex may represent a partial re-activation of motor circuitry involved in initiating and planning of motor sequence implying by verb meaning. Such motor re-activation may be redundant for verbs strongly associated with their nouns, since in this case fast activation spreading across the strong links of pre-formed purely linguistic associative network is sufficient for retrieving the intended verb synchronously with semantic processing of the presented noun (Butorina et al, 2017). After the failure of automatic verb retrieval, the following additional activation of shared motor representations may play a supportive role in the selection of the weakly associated verbs from semantic memory.…”

“…The stimuli list comprised 65 Russian nouns with a single strong verb associate and 65 nouns that were weakly associated with many verbs. The nouns were selected in an independent norming study (for details see Butorina et al, 2017). If the majority of the norming sample (from 58% to 90%) responded with the same verb to a presented noun, the noun was included into the Strong Association (SA) category (e.g., ''solovey-poyet/nightingale-sings'').…”