Brain and Language 97 (2006) 279–293 www.elsevier.com/locate/b&l 0093-934X/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.bandl.2005.11.003 Neural localization of semantic context eVects in electromagnetic and hemodynamic studies Cyma Van Petten a,¤ , Barbara J. Luka b a Department of Psychology, University of Arizona, Tucson, AZ 85721, USA b Bard College, USA Accepted 3 November 2005 Available online 15 December 2005 Abstract Measures of electrical brain activity (event-related potentials, ERPs) have been useful in understanding language processing for sev- eral decades. Extant data suggest that the amplitude of the N400 component of the ERP is a general index of the ease or diYculty of retrieving stored conceptual knowledge associated with a word, which is dependent on both the stored representation itself, and the retrieval cues provided by the preceding context. Recordings from patients with brain damage, intracranial recordings, and magnetoen- cephalographic data implicate a (probably large portion of) the left temporal lobe as the largest source of the N400 semantic context eVect, with a substantial but lesser contribution from the right temporal lobe. Event-related functional magnetic resonance (fMRI) studies using semantic context manipulations are dominated by observations of greater hemodynamic activity for incongruent sentence comple- tions or semantically unrelated words than congruent or related words, consistent with the direction of the ERP eVect. The locations of the hemodynamic eVects show some variability across studies, but one commonly identiWed region is the left superior temporal gyrus, which is compatible with the electrophysiological results. A second commonly identiWed region in the fMRI studies is the left inferior frontal gyrus, which does not appear to make a substantial contribution to the N400 eVect.  2005 Elsevier Inc. All rights reserved. Keywords: Event-related potential; N400; Magnetoencephalography; Functional magnetic resonance imaging; Brain damage; Aphasia; Semantic context 1. Introduction Event-related brain potentials (ERPs) are small Xuctua- tions in voltage, typically recorded noninvasively from the scalp, as participants process external stimuli and/or make overt motor responses. ERPs are the summation of synap- tic potentials that are time-locked (synchronized) with stim- ulus presentation or motor responses. These synaptic potentials are almost exclusively cortical in origin, and are likely to arise primarily from the principal cell type of the cerebral cortex, pyramidal cells (Allison, Wood, & McCar- thy, 1986; Regan, 1989; Nunez, 1981). In cognitive ERP research, the continuously varying waveform of voltage across time is conventionally carved up into “components” deWned by their polarity (positive- or negative-going), latency, spatial distribution across the scalp, and functional sensitivity to experimental manipulation. Many distinct components of the ERP have proven use- ful for understanding diVerent aspects of language process- ing (see Kutas, Van Petten, & Kluender, in preparation for a more extensive review). For instance, components reXect- ing motor programming and response inhibition have been applied to speech production (the Lateralized Readiness Potential and no-go N2; Schmitt, Schlitz, Zaake, Kutas, & Münte, 2001; van Turennout, Hagoort, & Brown, 1998). A component that indexes the perceptual familiarity of audi- tory patterns (Mismatch Negativity) has been useful in understanding how the processing of phonemes from one’s native language diVers from processing phonemes of an unknown language, and in tracking the acquisition of the phonological patterns of a Wrst or second language (Cheour et al., 1998; Näätänen et al., 1997). Distinct ERP components that may or may not be speciWc to morpholog- * Corresponding author. E-mail address: vanpettc@u.arizona.edu (C. Van Petten).