Incidental effects of emotional valence in single word processing: An fMRI study Lars Kuchinke, a, * Arthur M. Jacobs, a Claudia Grubich, b,c Melissa L.-H. Vo ˜, a Markus Conrad, a and Manfred Herrmann b,c a Department of Psychology, Free University of Berlin, Habelschwerdter Allee 45, 14195 Berlin, Germany b Department of Neuropsychology and Behavioral Neurobiology, Bremen University, Germany c Center for Advanced Imaging, Bremen, Germany Received 14 April 2005; revised 27 June 2005; accepted 28 June 2005 Available online 8 August 2005 The present study aimed at identifying the neural responses associated with the incidental processing of the emotional valence of single words using event-related functional magnetic resonance imaging (fMRI). Twenty right-handed participants performed a visual lexical decision task, discriminating between nouns and orthographically and phono- logically legal nonwords. Positive, neutral and negative word categories were matched for frequency, number and frequency of orthographic neighbors, number of letters and imageability. Response times and accuracy data differed significantly between positive and neutral, and positive and negative words respectively, thus, replicating the findings of a pilot study. Words showed distributed, mainly left hemisphere activations, indicating involvement of a neural network responsible for semantic word knowledge. The neuroimaging data further revealed areas in left orbitofrontal gyrus and bilateral inferior frontal gyrus with greater activation to emotional than to neutral words. These brain regions are known to be involved in processing semantic and emotional information. Furthermore, distinct activations associated with positive words were observed in bilateral middle temporal and superior frontal gyrus, known to support semantic retrieval, and a distributed network, namely anterior and posterior cingulate gyrus, lingual gyrus and hippocampus when comparing positive and negative words. The latter areas were previously associated with explicit and not incidental processing of the emotional meaning of words and emotional memory retrieval. Thus, the results are discussed in relation to models of processing semantic and episodic emotional information. D 2005 Elsevier Inc. All rights reserved. Keywords: Emotional valence; Positive, neutral, negative words; Lexical Decision Task; Semantic Memory; fMRI; Neuroimaging Introduction The last decade has produced many neuroimaging studies investigating the fundamental functions of memory and emotion. Most of these studies focused on effects of episodic memory during encoding and recognition of emotional contents. Both, recent event-related potential (ERP) studies and neuroimaging experiments revealed a number of cortical regions or electro- physiological correlates associated with the processing of the emotional valence of pictures (Anders et al., 2004; Lane et al., 1999; Smith et al., 2004; Taylor et al., 1998), sentences (Maratos et al., 2001; Maratos and Rugg, 2001) or words (Cato et al., 2004; Crosson et al., 1999; Dolcos et al., 2004; Hamann and Mao, 2002, Windmann and Kutas, 2001). For example, having subjects process verbal information during a word generation task, Cato et al. (2004) found activity in rostral frontal and retrosplenial cortical areas for both positive and negative stimuli using event-related fMRI design. The authors suggest that these findings correspond to the processing of emotional connotations as a semantic attribute. Taken together, these studies show an enhanced processing of emotional information in both hemispheres involving the inferior frontal gyrus and a cortico-limbic circuit including the amygdala, the hippocampal formation and the posterior cingulate gyrus (LeDoux, 1995; for reviews, see: Dolan, 2002; Hamann, 2001; Wager et al., 2003). Beyond this functionality and connectivity of the explicit memory system for different stimulus types, relatively little is known about the cortical network responsible for emotional effects in word recognition. While most of the above mentioned studies investigated attentional processing of affective valence, the question occurs, whether emotional valence effects of verbal stimuli can be seen when the meaning of the experimental stimuli is processed incidentally? Some researchers claimed that in situations where previously encoded information is subsequently processed without any conscious recollection subjects’ performance is not affected by the emotional valence of words (Danion et al., 1995; Nugent and Mineka, 1994; Parrot et al., 2005). One prominent paradigm for investigating this issue is the lexical decision task (LDT). In the LDT, subjects categorize stimuli as words or nonwords. Although they do not have to explicitly process the meaning of the words, it can be shown that different semantic features influence reaction 1053-8119/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.neuroimage.2005.06.050 * Corresponding author. E-mail address: kuchinke@zedat.fu-berlin.de (L. Kuchinke). Available online on ScienceDirect (www.sciencedirect.com). www.elsevier.com/locate/ynimg NeuroImage 28 (2005) 1022 – 1032