Xianxin Meng

THE VALENCE STRENGTH OF NEGATIVE STIMULI MODULATES VISUAL NOVELTY PROCESSING: ELECTROPHYSIOLOGICAL EVIDENCE FROM AN EVENT-RELATED POTENTIAL STUDY

In natural settings, the occurrence of unpredictable infrequent events is often associated with emotional reactions in the brain. Previous research suggested a special sensitivity of the brain to valence differences in emotionally negative stimuli. Thus, the present study hypothesizes that valence changes in infrequent negative stimuli would have differential effects on visual novelty processing. Event-related potentials (ERPs) were recorded for highly negative (HN), moderately negative (MN) and Neutral infrequent stimuli, and for the frequent standard stimulus while subjects performed a frequent/infrequent categorization task, irrespective of the emotional valence of the infrequent stimuli. The infrequent-frequent difference waves, which index visual novelty processing, displayed larger N2 amplitudes during HN condition than during MN condition which, in turn, elicited greater N2 amplitude than the Neutral condition. Similarly, in the infrequent-frequent difference waves, the frontocentral P3a and parietal LPC (late positive complex) elicited by the HN condition were more negative than those by MN stimuli, which elicited more negative amplitudes than the Neutral condition. This suggests that negative emotions of diverse strength, as induced by negative stimuli of varying valences, are clearly different in their impact on visual novelty processing. Novel stimuli of increased negativity elicited more attentional resources during the early novelty detection, and recruited increased inhibitive and evaluative processing during the later stages of response decision and reaction readiness, relative to novel stimuli of reduced negativity.

The valence strength of unpleasant emotion modulates brain processing of behavioral inhibitory control: neural correlates.

As an ability critical for adaptive social living, behavioral inhibitory control (BIC) is known to be influenced substantially by unpleasant emotion. Nevertheless, how unpleasant emotion of diverse strength influences this control, and the spatiotemporal dynamics underlying this influence, remain undetermined. For this purpose, Event-related potentials (ERPs) were recorded for standard stimulus which required no BIC, and for deviant stimuli that required controlling habitual responses, during highly unpleasant (HU), mildly unpleasant (MU) and Neutral blocks. The results showed delayed response latencies for deviant compared to standard stimuli, irrespective of emotionality. Moreover, there were significant main effects of stimulus type, and significant stimulus type and block interaction effects on the averaged amplitudes of the 230-310 ms and 330-430 ms intervals. In the deviant-standard difference waves which directly index BIC-relevant processing, these interactions were manifested by increased negative potentials as a function of the strength of unpleasant emotion across N2 and P3 components. In addition, these influences are specific to unpleasant emotion, as pleasant emotion of diverse strength produced a similar impact in the control experiment. Therefore, unpleasant emotion of diverse strength is different in impact on brain processing of behavioral inhibitory control. This impact is evident not only in early monitoring of response conflicts, but also in late processing of response inhibition.

The impact of emotion valence on brain processing of behavioral inhibitory control: spatiotemporal dynamics.

Emotion is known to interact with behavioral inhibitory control (BIC), an ability critical for adaptive living. Nevertheless, how emotion valence influences this control, and the spatiotemporal dynamics underlying this influence, remain undetermined. For this purpose, the present study recorded event-related potentials (ERPs) for a standard stimulus which required no BIC, and for deviant stimuli that required controlling habitual responses during pleasant, neutral and unpleasant blocks. Behavioral results showed prolonged reaction times (RTs) and diminished accuracy rates for deviant than for standard stimuli, irrespective of the emotionality of deviants. Moreover, there were significant main effects of stimulus type, and significant stimulus and emotion interaction effects on the averaged amplitudes of the 200-300ms and 300-500ms intervals. Through analyzing the deviant-standard difference ERPs that index BIC directly, we found larger N2 and smaller P3 amplitudes during the unpleasant block than during the neutral block. The pleasant block, in contrast, showed a trend of more pronounced P3 amplitudes than the neutral block. Thus, by synchronizing BIC with emotion induction, we found distinct impact of pleasant and unpleasant emotions on behavioral inhibitory processing, not only in early monitoring of response conflicts but also in the late stage of response inhibition.

Neural mechanisms underlying the higher levels of subjective well-being in extraverts: Pleasant bias and unpleasant resistance

The present study investigated the neural mechanisms that underlie the higher levels of subjective well-being in extraverts. The impact of extraversion on the human sensitivity to pleasant and unpleasant pictures of diverse emotional intensities was examined. We recorded event-related potentials (ERPs) for highly positive (HP), moderately positive (MP), and neutral stimuli in the pleasant session, and for highly negative (HN), moderately negative (MN), and neutral stimuli in the unpleasant session, while subjects (16 extraverts and 16 ambiverts) performed a standard/deviant categorization task, irrespective of the emotionality of the deviant stimuli. The results showed significant emotion effects for HP and MP stimuli at the P2 and P3 components in extraverts, but not in ambiverts. Despite a pronounced emotion effect for HN stimuli across the P2, N2, and P3 components in both samples, ambiverts displayed a significant emotion effect for MN stimuli at the N2 and P3 components that was absent in extraverts. The posterior cingulate cortices, which connect multiple neural regions that are important in interactions of emotion and extraversion, may mediate the extravert-specific emotion effect for pleasant stimuli. Thus, extraverts are less susceptible to unpleasant stimuli of mild intensity than are ambiverts, while extraverts have an additional enhanced sensitivity to pleasant stimuli, regardless of emotion intensity. Consequently, the decreased threshold for pleasant emotion and the increased threshold for unpleasant emotion might be essential neural mechanisms that underlie the higher levels of subjective well-being in extraverts.

Automatic processing of valence differences in emotionally negative stimuli: evidence from an ERP study.

The present study investigated the influence of attention on the human sensitivity to valence differences in emotionally negative stimuli. Event-related potentials were recorded for unattended highly negative (EN), moderately negative (MN) and neutral pictures in Experiment 1 which engaged subjects in an auditory discrimination task; and for EN, MN and neutral pictures in Experiment 2 that required visual classification of pictures. Results of both experiments displayed increased negative deflections during EN than during MN and neutral conditions at 150-250, 250-350, and 350-450 ms intervals post-stimulus. Moreover, MN stimuli elicited larger negativity than did neutral stimuli during 250-350 ms interval in either experiment. This developed our understanding of the human sensitivity to valence differences in negative stimuli, by revealing that the brain sensitivity to the valence strength of negative stimuli exists stably, unaffected by attention access to some extent.

Enhanced brain susceptibility to negative stimuli in adolescents: ERP evidences

Background: Previous studies investigated neural substrates of emotional face processing in adolescents and its comparison with adults. As emotional faces elicit more of emotional expression recognition rather than direct emotional responding, it remains undetermined how adolescents are different from adults in brain susceptibility to emotionally stressful stimuli. Methods: Event-Related Potentials (ERPs) were recorded for highly negative (HN), moderately negative (MN), and neutral pictures in 20 adolescents and 20 adults while subjects performed a standard/deviant distinction task by pressing different keys, irrespective of the emotionality of deviant stimuli. Results: Adolescents exhibited more negative amplitudes for HN vs. neutral pictures in N1 (100–150 ms), P2 (130–190 ms), N2 (210–290 ms), and P3 (360–440 ms) components. In addition, adolescents showed more negative amplitudes for MN compared to neutral pictures in N1, P2, and N2 components. By contrast, adults exhibited significant emotion effects for HN stimuli in N2 and P3 amplitudes but not in N1 and P2 amplitudes, and they did not exhibit a significant emotion effect for MN stimuli at all these components. In the 210–290 ms time interval, the emotion effect for HN stimuli was significant across frontal and central regions in adolescents, while this emotion effect was noticeable only in the central region for adults. Conclusions: Adolescents are more emotionally sensitive to negative stimuli compared to adults, regardless of the emotional intensity of the stimuli, possibly due to the immature prefrontal control system over the limbic emotional inputs during adolescence.

Enhanced sensitivity to rare, emotion-irrelevant stimuli in females: neural correlates.

Numerous studies showed enhanced sensitivity of females to emotional stimuli relative to males using multiple tasks. However, in the present study, two event-related potential (ERP) experiments targeting the impact of gender on rare stimulus processing both showed enhanced sensitivity of females to rare stimulus that is neutral, irrelevant to emotion. Subjects were required to press different keys for standard and rare pictures in Experiment 1, and to do nothing but to passively view the pictures in Experiment 2. Rare pictures elicited more intense pop-out effects in females, at both neuroelectrical (multiple levels of ERP analyses) and behavioral (response latencies and pop-out assessment) levels across experiments. Thus, females are equipped with enhanced sensitivity to rare, emotion-irrelevant stimuli relative to males, probably as a result of evolutionary adaptation. This effect is ought to be considered in studies that use an oddball paradigm.

The impact of extraversion on attentional bias to pleasant stimuli: Neuroticism matters

The present study explored whether neuroticism modulates the impact of extraversion on attention orienting to pleasant and unpleasant pictures of diverse emotional intensities. We measured event-related potentials for highly emotional, mildly emotional, and neutral stimuli in both pleasant and unpleasant blocks, while subjects (16 stable ambiverts, 15 stable extraverts, 17 neurotic ambiverts, and 17 neurotic extraverts) were asked to perform a standard/deviant categorization task, irrespective of the emotionality of the deviants. The results revealed a modulation effect of neuroticism in the impact of extraversion on emotional attention. On the one hand, irrespective of extraversion, emotionally stable samples showed increased N200 amplitudes for highly unpleasant (HN) stimuli relative to mildly unpleasant (MN) and neutral stimuli, while these samples exhibited no significant emotion magnitude effect in the pleasant block. On the other hand, although neurotic samples, both extraverts and ambiverts, showed enhanced N2 amplitudes for HN stimuli than neutral stimuli, neurotic extraverts displayed increased N2 amplitudes for highly pleasant (HP) and mildly pleasant (MP) stimuli than neutral stimuli, which was absent in neurotic ambiverts. These results extend our understanding of the relationship between extraversion and emotion by showing that neuroticism amplifies the positive emotional bias of extraverts.

The impact of emotion intensity on recognition memory: Valence polarity matters

Although the effects of emotion of different emotional intensity on memory have been investigated, it remain unclear whether the influence of emotional intensity on memory varies depending on the stimulus valence polarity (i.e., positive or negative). To address this, event-related potentials were recorded when subjects performed a continuous old/new discrimination task, for highly negative (HN), mildly negative (MN) and neutral pictures in the negative session; and for highly positive (HP), mildly positive (MP) and neutral pictures in the positive session. The results showed that relative to neutral stimuli, both HN and MN stimuli showed increased memory discrimination scores, and enhanced old/new effect in early FN400 (Frontal Negativity), but not late positive component (LPC) amplitudes. By contrast, relative to MP stimuli, HP and neutral stimuli showed increased memory discrimination scores and enhanced old/new effect in LPC but not FN400 amplitudes. Additionally, we observed a significant positive correlation between the memory discrimination score and the old/new effect in the amplitudes of the FN400 and LPC, respectively. These results indicate that both HN and MN stimuli were remembered better than neutral stimuli; whereas the recognition was worse for MP stimuli than Neutral and HP stimuli. In conclusion, in the present study, we observed that the effect of emotion intensity on memory depends on the stimulus valence polarity.

EEG Oscillation Evidences of Enhanced Susceptibility to Emotional Stimuli during Adolescence.

Background: Our recent event-related potential (ERP) study showed that adolescents are more emotionally sensitive to negative events compared to adults, regardless of the valence strength of the events. The current work aimed to confirm this age-related difference in response to emotional stimuli of diverse intensities by examining Electroencephalography (EEG) oscillatory power in time-frequency analysis. Methods: Time-frequency analyses were performed on the EEG data recorded for highly negative (HN), moderately negative (MN) and Neutral pictures in 20 adolescents and 20 adults during a covert emotional task. The results showed a significant age by emotion interaction effect in the theta and beta oscillatory power during the 500–600 ms post stimulus. Results: Adolescents showed significantly less pronounced theta synchronization (ERS, 5.5–7.5 Hz) for HN stimuli, and larger beta desynchronization (ERD; 18–20 Hz) for both HN and MN stimuli, in comparison with neutral stimuli. By contrast, adults exhibited no significant emotion effects in theta and beta frequency bands. In addition, the analysis of the alpha spectral power (10.5–12 Hz; 850–950 ms) showed a main effect of emotion, while the emotion by age interaction was not significant. Irrespective of adolescents or adults, HN and MN stimuli elicited enhanced alpha suppression compared to Neutral stimuli, while the alpha power was similar across HN and MN conditions. Conclusions: These results confirmed prior findings that adolescents are more sensitive to emotionally negative stimuli compared to adults, regardless of emotion intensity, possibly due to the developing prefrontal control system during adolescence.