Neural correlates of emotion word processing: the interaction between emotional valence and arousal

Emotion is characterised by two-dimensions: emotional valence describes the extent to which an emotion is positive or negative, and arousal represents its intensity. Emotional content of verbal material affects cognitive processing, although research on word recognition has only recently taken emotion into account, primarily focusing on valence, while neglecting arousal. The present work aimed to disentangle the effects of valence and arousal during a lexical decision task, using reaction times (RTs), event-related potentials (ERPs) and BOLD responses in an event-related fMRI design. These methods were chosen to determine when affective features have an effect, and which neural systems are involved. The material for three experiments was based on a word corpus created by collecting ratings for emotional and lexico-semantic features. A first and novel finding was that arousal interacted with valence. Specifically, lexical decision times were slower for high-arousal positive stimuli (PH) and low-arousal negative ones (NL) compared to low-arousal positive (PL) and high arousal negative (NH) stimuli. ERPs also showed an interaction between 200-300 ms on the early posterior negativity (EPN), a component which is sensitive to emotional stimuli. At this processing stage people access their mental lexicon. Its amplitude was greater for PH and NL words, suggesting a higher processing load for conflicting stimuli. Positive valence and low arousal elicit an approach schema, whereas negative valence and high arousal elicit an avoidance schema (Robinson, Storbeck, Meier & Kirkeby, 2004). BOLD responses showed a similar interaction in the insula bilaterally, with increased activation for PH and NL words. This region is associated with integration of information on visceral states with higher-order cognitive and emotional processing, suggesting higher difficulty in integrating conflicting stimuli. Taken together, these studies indicate that emotion affects word processing during lexical access, and models of word recognition need to take into account both valence and arousal