Amygdala activation during reading of emotional adjectives--an advantage for pleasant content

Abstract

This event-related functional magnetic resonance imaging (fMRI) study investigated brain activity elicited by emotional adjectives during silent reading without specific processing instructions. Fifteen healthy volunteers were asked to read a set of randomly presented high-arousing emotional (pleasant and unpleasant) and low-arousing neutral adjectives. Silent reading of emotional in contrast to neutral adjectives evoked enhanced activations in visual, limbic and prefrontal brain regions. In particular, reading pleasant adjectives produced a more robust activation pattern in the left amygdala and the left extrastriate visual cortex than did reading unpleasant or neutral adjectives. Moreover, extrastriate visual cortex and amygdala activity were significantly correlated during reading of pleasant adjectives. Furthermore, pleasant adjectives were better remembered than unpleasant and neutral adjectives in a surprise free recall test conducted after scanning. Thus, visual processing was biased towards pleasant words and involved the amygdala, underscoring recent theoretical views of a general role of the human amygdala in relevance detection for both pleasant and unpleasant stimuli. Results indicate preferential processing of pleasant information in healthy young adults and can be accounted for within the framework of appraisal theory.

Fig. 1

(A) Shows brain activity elicited by emotional as compared to neutral adjectives during silent reading. Right panels provide an overview on cortical activation and left panels on amygdala activation for contrasts between neutral adjectives and emotional, pleasant or unpleasant adjectives, respectively. For visualization, functional brain activation maps are superimposed on a rendered brain incorporated in the SPM99 software package and on T1-weighted images from MRIcro software (http://www.sph.sc.edu/comd/rorden/mricro.html). Effects are displayed at a threshold of P < 0.005 uncorrected, (T-score > 3) with a spatial extend threshold of 20 contiguous voxels. For contrasts comparing unpleasant against neutral adjectives, activation is displayed at a more lenient threshold of P = 0.05 uncorrected (T-score > 1.76) to illustrate the general pattern. (B) Amygdala and extrastriate activity obtained from a ROI analysis of the left amygdala and the left extrastriate cortex. Significant correlation (r = 0.66; P < 0.001) between peak signal change in the left amygdala and the left extrastriate cortex (peak at −48 −76 −2) elicited by pleasant adjectives relative to baseline conditions.

Fig. 2

Memory advantage for pleasant adjectives during the surprise free recall test. Bars (±s.e.) represent numbers of correctly remembered pleasant, unpleasant and neutral adjectives. Significant differences are marked with asterisks.