N400-like Magnetoencephalography Responses Modulated by Semantic Context, Word Frequency, and Lexical Class in Sentences

Abstract

Words have been found to elicit a negative potential at the scalp peaking at ϳ400 ms that is strongly modulated by semantic context. The current study used whole-head magnetoencephalography (MEG) as male subjects read sentences ending with semantically congruous or incongruous words. Compared with congruous words, sentence-terminal incongruous words consistently evoked a large magnetic field over the left hemisphere, peaking at ϳ450 ms. Source modeling at this latency with conventional equivalent current dipoles (ECDs) placed the N400m generator in or near the left superior temporal sulcus. A distributed solution constrained to the cortical surface suggested a sequence of differential activation, beginning in Wernicke's area at ϳ250 ms, spreading to anterior temporal sites at ϳ270 ms, to Broca's area by ϳ300 ms, to dorsolateral prefrontal cortices by ϳ320 ms, and to anterior orbital and frontopolar cortices by ϳ370 ms. Differential activity was exclusively left-sided until >370 ms, and then involved right anterior temporal and orbital cortices. At the peak of the N400m, activation in the left hemisphere was estimated to be widespread in the anterior temporal, perisylvian, orbital, frontopolar, and dorsolateral prefrontal cortices. In the right hemisphere, the orbital, as well as, weakly, the right anterior temporal cortices were activated. Similar but weaker field patterns were evoked by intermediate words in the sentences, especially to low-frequency words occurring in early sentence positions where there is little preceding context. The locations of the N400m sources identified with the distributed solution correspond well with those previously demonstrated with direct intracranial recordings, and suggested by functional magnetic resonance imaging (fMRI). These results help identify a distributed cortical network that supports online semantic processing. © 2002 Elsevier Science (USA)

A Neurocomputational Model of the N400 and the P600 in Language Processing

“…What is more, the lpMTG is the only region that is active at both short and long stimulus onset asynchronies in lexical semantic priming studies (see Lau et al., 2008, for a large‐scale review), supporting the idea that it plays a crucial role in the generation of the N400 component. This is consistent with source localization of the N400m, the magnetic field equivalent of the N400, which also points to the lpMTG as its main generator (Halgren et al., 2002). Finally, the lpMTG shows a particularly rich pattern of connectivity, both structurally and functionally, to frontal, parietal, and temporal regions of both hemispheres (Turken & Dronkers, 2011; see also Binder et al., 2009; Buckner et al., 2009; Koyama et al., 2010), supporting its role as a memory epicenter that retrieves and binds together conceptual knowledge from the association cortices, across which it is stored in a distributed manner.…”

Event-Related Brain Potentials in the Study of Inhibition: Cognitive Control, Source Localization and Age-Related Modulations

“…As Debruille's inhibition hypothesis did not refer to a specific N400, as opposed to the N400 linked to semantic integration, we briefly address 45 the results of source localization studies conducted with paradigms that did not directly address the inhibition hypothesis. These studies used MEG (Halgren et al 2002;Lau et al 2009) and high density EEG (Silva-Pereyra et al 2003;Kuperberg et al 2003) and identified generators for the N400 effect in temporal (i.e., Wernicke's area and anterior temporal cortex) and frontal (i.e., dorsolateral, orbital and anterior prefrontal cortices) areas.…”

Localizing the distributed language network responsible for the N400 measured by MEG during auditory sentence processing

“…Data from more superficial intracranial recordings, however, suggest that the superior temporal sulcus and additional frontal areas are involved in the generation of the N400 (Halgren et al, 1994a,b). A spatially more global approach is the use of whole-head MEG recording (Marinkovic et al, 2003;Halgren et al, 2002;Helenius et al, 1998Helenius et al, , 2002 to identify the generators of the N400. Several studies reported structures in the "immediate vicinity of the auditory cortex" to be implicated most consistently with the processing of semantically anomalous sentences using equivalent current dipole analysis (Helenius et al, 2002;Mäkelä et al, 2001;Halgren et al, 2002).…”

“…Recently, distributed source modeling has been applied to MEG data to specify the areas involved in the generation of the N400 during reading semantically incongruent sentences (Halgren et al, 2002). The analysis identified quite a number of structures involved in processes reflected by the N400, namely, the left planum temporale, the left superior and inferior temporal sulci, the left temporal pole and the rhinal sulcus, the left insula, and the collateral sulcus at the occipitotemporal junction, the left prefrontal cortex (gyrus rectus, inferior frontal gyrus, dorsolateral prefrontal, and frontopolar cortices), as well as the right orbital cortex.…”