Nonemotional features suppress early and enhance late emotional electrocortical responses to negative pictures

Neural processing of emotional pictures is often indexed by two electrocortical responses: the early posterior negativity (EPN) and the late positive potential (LPP). Because emotional pictures vary in nonemotional features (e.g., composition, human content, and spatial frequency), researchers often match pictures on nonemotional features to avoid their confounding effects on the EPN and LPP. However, this matching is tedious and might be unnecessary if the confounding effects could be shown to be negligible. In an item-analysis of mean amplitudes to 400 negative to neutral pictures from the International Affective Picture System (IAPS), nonemotional features had larger effects on EPN than LPP. Picture composition suppressed the relationship between emotion and EPN. Further, data simulations showed that for small picture sets, nonemotional features inflated the correlation between emotion and LPP. Therefore, nonemotional features suppress the EPN and enhance the LPP, particularly so in small picture sets.     

Emotional event-related potentials are reduced if negative pictures presented at fixation are unattended

Viewing of emotional pictures elicits two event-related potentials (ERPs) to emotional versus neutral pictures: an early posterior negativity (EPN) and a late positive potential (LPP). Because it is unresolved whether these indexes of emotional processing are reduced to task-irrelevant pictures at fixation, negative and neutral pictures from the International Affective Picture Set (IAPS) were shown at fixation together with 6 letters that surrounded the pictures. In separate tasks, participants were instructed to attend either the pictures or the letters. When the pictures were task relevant, results showed an EPN and LPP. In contrast, when the pictures were task irrelevant, the EPN was eliminated and the LPP reduced. Performance was high in both tasks (hit rates>87%), but somewhat better when the pictures were relevant. However, analyses showed no relationship between this performance difference and the differences in EPN and LPP between tasks. These results suggest that emotional processing of strong, negative pictures is sensitive to manipulations of attention even if the pictures are shown at fixation.     

The neural processing of fearful faces without attention and consciousness: an event-related potential study

To investigate whether the non-conscious processing of fearful faces exist in unattended condition, event-related potentials (ERPs) were recorded in a facial expression detection task. Participants were asked to discriminate the facial expressions (fearful or neutral) at the attended location. Unattended faces were associated with a response that was either congruent or in conflict with the response to the attended face. ERP results showed that the trials with response conflict between attended and unattended faces enhanced the amplitude of the P3 component when the neutral face was presented at attended location and the fearful face was presented at the unattended location. Our findings imply that the non-conscious fearful faces can be processed in the unattended condition.     

Time course of attentional modulations on automatic emotional processing

In a previous study using event-related potentials (ERPs) [S. Doallo, S. Rodríguez Holguín, F. Cadaveira, Attentional load affects automatic emotional processing: evidence from event-related potentials, Neuroreport 17 (2006) 1797-1801], we reported that differential responses to unattended peripheral affective pictures, as reflected by N1-P2 modulations at posterior regions, are modulated by attentional load at fixation. Here, new analyses of these data were performed to evaluate whether a sustained, broadly distributed, negative shift in the unattended pictures ERP waveforms, which displayed larger amplitudes for emotional stimuli, reflects an additional differential response to the emotional content. Under low-load conditions, unpleasant (versus neutral) pictures elicited greater negativities in the 80-140 ms latency range over frontocentral sites and more centroparietally distributed from 200 to 280 ms. These findings provide further evidence of the time course of emotional processing at unattended locations and its modulation by attentional load.     

Up-regulation of emotional responses to reward-predicting stimuli: An ERP study

Altered reward processing is a hallmark symptom of many psychiatric disorders. It has recently been shown that people are capable of down-regulating reward processing. Here, we examined whether people are capable of up-regulating emotional responses to reward-predicting stimuli. Participants passively viewed colored squares that predicted a reward or no reward, and up- or down-regulated their emotional responses to these reward-predicting stimuli by focusing on the reward meaning or the color of the squares respectively. The amplitude of the late positive potential (LPP) was taken as an objective index of regulation success. The LPP in response to reward-predicting squares was enhanced by up-regulation, suggesting that up-regulation of emotional responses to reward-predicting stimuli using a cognitive strategy is feasible. These results are highly relevant for the treatment of disorders characterized by diminished motivation, and for reward-based decision making in daily life.     

Word frequency modulates the processing of emotional words: convergent behavioral and electrophysiological data

The processing of high frequency (HF) words is speeded as compared to the processing of low frequency (LF) words, which is known as the word frequency effect. This effect has been suggested to occur at either a lexical access or in a decision processing stage. Previous work has shown that word frequency influenced the processing of emotional content at both neural and behavioral levels. However, the results of these studies lead to discrepant findings because some of the variables that have shown to impact the processing of affective information were not always controlled. In order to make a better characterization of frequency effects on emotional word processing, event related potentials (ERPs) and reaction times to HF and LF negative and neutral nouns were measured as participants performed a lexical decision task. Temporal and spatial component analyses were used to detect and quantify, in a reliable way, those components associated with the interaction between word frequency and emotion. LF negative nouns were recognized faster and more accurately than LF neutral nouns whereas no differences were found in the HF word comparison. Also, LF neutral words elicited reduced amplitudes in a late positive component (P450) as compared to LF negative words. These findings might be reflecting a different involvement of attentional mechanisms during the evaluation of lexical information that benefits the processing of LF negative nouns.     

Tonic pain grabs attention, but leaves the processing of facial expressions intact-evidence from event-related brain potentials

Emotion and attention are key players in the modulation of pain perception. However, much less is known about the reverse influence of pain on attentional and especially emotional processes. To this end, we employed painful vs. non-painful pressure stimulation to examine effects on the processing of simultaneously presented facial expressions (fearful, neutral, happy). Continuous EEG was recorded and participants had to rate each facial expression with regard to valence and arousal. Painful stimulation attenuated visual processing in general, as reduced P100 and late positive potential (LPP) amplitudes revealed, but did not interfere with structural encoding of faces (N170). In addition, early perceptual discrimination and sustained preferential processing of emotional facial expressions as well as affective ratings were not influenced by pain. Thus, tonic pain demonstrates strong attention-demanding properties, but this does not interfere with concurrently ongoing emotion discrimination processes. These effects point at partially independent effects of pain on emotion and attention, respectively.     

See no evil: directing visual attention within unpleasant images modulates the electrocortical response

The late positive potential (LPP) is larger for emotional than neutral stimuli, and reflects increased attention to motivationally salient stimuli. Recent studies have shown that the LPP can also be modulated by stimulus meaning and task relevance. The present studies sought to determine whether the magnitude of the LPP can be manipulated by directing attention to more or less arousing aspects within an emotional stimulus. To this end, trials included a passive viewing and directed attention portion. In both Studies 1 and 2, unpleasant compared to neutral images were associated with an increased LPP during passive viewing; additionally, directing attention to non-arousing compared to highly arousing areas of unpleasant images resulted in a decreased LPP. Results are discussed in terms of the utility of using the LPP to understand emotion–cognition interactions, especially with regard to directed visual attention as an emotion regulation strategy.     

Affective picture processing as a function of preceding picture valence: an ERP analysis

Event-related brain potential (ERP) studies consistently revealed that a relatively early (early posterior negativity; EPN) and a late (late positive potential; LPP) ERP component differentiate between emotional and neutral picture stimuli. Two studies examined the processing of emotional stimuli when preceded either by pleasant, neutral, or unpleasant context images. In both studies, distinct streams of six pictures were shown. In Study 1, hedonic context was alternated randomly across the 180 picture streams. In Study 2, hedonic context sequences were blocked, resulting in 60 preceding sequences of pleasant, neutral, and unpleasant context valence, respectively. The main finding was that the valence of the preceding picture sequence had no significant effect on the emotional modulation of the EPN and LPP components. However, previous results were replicated in that emotional stimulus processing was associated with larger EPN and LPP components as compared to neutral pictures. These findings suggest that the prioritized processing of emotional stimuli is primarily driven by the valence of the current picture.     

Healthy aging is associated with increased neural processing of positive valence but attenuated processing of emotional arousal: an fMRI study

Arousal and valence play key roles in emotional perception, with normal aging leading to changes in the neural substrates supporting valence processing. The objective of this study was to investigate normal age-related changes in the neural substrates of emotional arousal processing. Twenty-three young and 23 older, healthy women underwent functional magnetic resonance imaging as they viewed images which were neutral or positive in valence and which varied in arousal level from low to high. Using a parametric modulation approach, we examined how the blood oxygen-level dependent signal varied with single trial subjective ratings of valence and arousal, and whether this differed with age. In accordance with previous studies we found that the older group showed greater activation in response to positive valence, in the left amygdala, left middle temporal gyrus and right lingual gyrus. In contrast however, they showed reduced reactivity to emotional arousal, in occipital and temporal visual cortices bilaterally, the left inferior parietal cortex, and the supplementary motor area bilaterally. This study represents the first of its kind to clearly dissociate how aging affects the neural correlates of emotional arousal and valence. The changes in arousal processing may in part be mediated by the functional reorganization evident in the aging brain, such as reduced activation of the posterior cortices as described by the posterior-anterior shift in ageing (PASA) effect.     

Timing effects of antecedent- and response-focused emotion regulation strategies

Distraction and cognitive reappraisal influence the emotion-generative process at early stages and have been shown to effectively attenuate emotional responding. Inhibiting emotion-expressive behavior is thought to be less beneficial due to later implementation, but empirical results are mixed. Thus, the current study examined the temporal dynamics of these emotion regulation strategies at attenuating the late positive potential (LPP) while participants were shown unpleasant pictures. Results revealed that all strategies successfully reduced the LPP and self-reported negative affect. We confirmed that distraction attenuated the LPP earlier than cognitive reappraisal. Surprisingly, expressive suppression affected emotional responding as early as distraction. This suggests that suppression was used preventively and disrupted the emotion-generative process from the very beginning instead of targeting the emotional response itself. Thus, the obtained results point to the importance of considering the point in time when response-focused emotion regulation strategies are being implemented.     

Probing affective pictures: Attended startle and tone probes

Reflexive eyeblinks to a startle probe vary with the pleasantness of affective pictures, whereas the corresponding P300 varies with emotional arousal. The impact of attention to the probe on these effects was examined by varying task and probe type. Probes were either nonstartling tones or startling noises presented during affective picture viewing. Half the participants performed a task requiring attention to the probes; the other participants were told to ignore the probes. Blinks to the startle probe varied with picture pleasantness for both task and nontask conditions. In contrast, P300 magnitudes for both startle and tone probes were reduced during emotionally arousing pictures, irrespective of pleasantness, in task and nontask conditions. Further, attending to the startle probe prompted an augmentation of N100 during unpleasant pictures. The data suggest that affective modulation of probe responses reflects obligatory processes in picture perception.     

Attentional capture by task-irrelevant fearful faces is revealed by the N2pc component

We measured the N2pc component as an electrophysiological indicator of attentional selection to investigate whether fearful faces can attract attention even when they are entirely task-irrelevant and attention is focused on another demanding visual monitoring task. Participants had to detect infrequent luminance changes of the fixation cross, while ignoring stimulus arrays containing a face singleton (a fearful face among neutral faces, or neutral face among fearful faces) to the left or right of fixation. On trials without a target luminance change, an N2pc was elicited by fearful faces presented next to fixation, irrespective of whether they were singletons or not, demonstrating that irrelevant fearful faces can bias the spatial distribution of attention. The N2pc to fearful faces was attenuated when face arrays were presented simultaneously with a target luminance change, suggesting that concurrent target processing reduces attentional capture by emotional salient events.     

Trait absorption is related to enhanced emotional picture processing and reduced processing of secondary acoustic probes

Trait absorption reflects a propensity to have one's attention drawn to engaging sensory or imaginal experiences. It is related to self‐reported levels of positive and negative emotionality, but little work has examined whether absorption is related to greater levels of basic emotional processing. We used the late positive potential (LPP) to pictures and P3 response to subsequent startle probes during those pictures to examine how absorption was related to initial emotional processing and reactivity to a second stimulus. Across genders, absorption was positively related to LPP amplitude to emotional versus neutral pictures at PZ, and it was negatively related to overall P3 amplitude to startle probes at FZ. Thus, absorption appears to index greater processing of emotional material at the cost of reduced processing of subsequent incoming stimuli.     

Brain potentials and behavioral responses associated with attention to hard- and easy-to-discriminate passive knee joint movements

We investigated event-related brain potentials (ERPs) to passive ramp movements of the knee joint. The knee movements were either attended or unattended and were either very easy or very hard to detect. We used special methods to ensure that movement only activated muscle spindle and joint receptors. The first movement-related ERP started 20 ms after movement onset, and had a contralateral maximum. This initial ERP did not differ as a function of attention and movement discriminability. Signal detection analysis of the behavioral data suggested that hard-to-detect movements could be discriminated above chance level, but were not reported because of a decision bias. At 60-100 ms, an ERP was observed that discriminated detected from undetected hard-to-detect movements. Starting at 80 ms, we found an ERP that was unique to movements that were attended and easy to detect. We discuss that (1) the initial ERP reflects activation of preconscious sensory processors, (2) the second ERP may reflect detection that fails to attract attention, and (3) the third ERP reflects active focusing of attention on the movement.     

Reprint of “Affective picture processing as a function of preceding picture valence: An ERP analysis”

Event-related brain potential (ERP) studies consistently revealed that a relatively early (early posterior negativity; EPN) and a late (late positive potential; LPP) ERP component differentiate between emotional and neutral picture stimuli. Two studies examined the processing of emotional stimuli when preceded either by pleasant, neutral, or unpleasant context images. In both studies, distinct streams of six pictures were shown. In Study 1, hedonic context was alternated randomly across the 180 picture streams. In Study 2, hedonic context sequences were blocked, resulting in 60 preceding sequences of pleasant, neutral, and unpleasant context valence, respectively. The main finding was that the valence of the preceding picture sequence had no significant effect on the emotional modulation of the EPN and LPP components. However, previous results were replicated in that emotional stimulus processing was associated with larger EPN and LPP components as compared to neutral pictures. These findings suggest that the prioritized processing of emotional stimuli is primarily driven by the valence of the current picture.     

Attention modulates emotional expression processing

To investigate the time course of emotional expression processing, we recorded ERPs to facial stimuli. The first task was to discriminate emotional expressions. Enhanced negativity of the face-specific N170 was elicited by emotional as opposed to neutral faces, followed by the occipital negativity (240-340 ms poststimulus). The second task was to classify face gender. Here, N170 was unaffected by the emotional expression. However, emotional expression effect was expressed in the anterior positivity (160-250 ms poststimulus) and subsequent occipital negativity (240-340 ms poststimulus). Results support the thesis that structural encoding relevant to gender recognition and simultaneous expression analysis are independent processes. Attention modulates facial emotion processing 140-185 ms poststimulus. Involuntary differentiation of facial expression was observed later (160-340 ms poststimulus), suggesting unintentional attention capture.     

Somatosensory responses during selective spatial attention: The N120-to-N140 trasition

The somatosensory evoked potential negative components in the 100–150-ms range were studied under conditions where attention was directed either toward or away from the probe stimulus. An N120 component, not sensitive to spatial attention, appeared in all conditions, including the no-task condition. Its distribution was consistent with an origin in the second somatic area. A later N140 response, not recorded in neutral conditions, was highly sensitive to spatial attention and reached its maximum to stimulation of the attended hand; its behavior was consistent with that of a processing negativity. The N140 was bilaterally distributed, but the hemisphere contralateral to stimulation appeared to be involved earlier than the ipsilateral one. Although the exogenous N120 may be influenced by somatosensory awareness and perhaps tactile recognition, the N140 appears linked to the spatial components of attention and results from the activation of several areas in both hemispheres.     

Electrophysiological correlates of decreasing and increasing emotional responses to unpleasant pictures

We examined event-related brain potential (ERP) modulations during the anticipation and processing of unpleasant pictures under instructions to cognitively decrease and increase negative emotion. Instructions to decrease and increase negative emotion modulated the ERP response to unpleasant pictures in the direction of emotional intensity beginning around 400 ms and lasting several seconds. Decrease, but not increase, instructions also elicited enhanced frontal negativity associated with orienting and preparation prior to unpleasant picture onset. Last, ERP modulation by unpleasant pictures began around 300 ms, just prior to regulation effects, suggesting that appraisal of emotion occurs before emotion regulation. Together, the current findings underscore the utility of ERPs in illuminating the time course of emotion modulation and regulation that may help to refine extant theoretical models.     

Physiological arousal and attention during a week of continuous sleep restriction

Waking brain physiology underlying deficits from continuous sleep restriction (CSR) is not well understood. Fourteen good sleepers participated in a 21-day protocol where they slept their usual amount in a baseline week, had their time in bed restricted by 33% in a CSR week, and slept the desired amount in a recovery week. Participants slept at home, completing diaries and wearing activity monitors to verify compliance. Each day participants completed an RT task and mood and sleepiness ratings every 3 h. Laboratory assessment of electrophysiology and performance took place at the end of baseline, three times throughout the CSR week, and at the beginning of recovery. Participants reported less sleep during CSR which was confirmed by activity monitors. Correspondingly, well-being and neurobehavioural performance was impaired. Quantitative EEG analysis revealed significantly reduced arousal between the 1st and 7th days of restriction and linear effects at anterior sites (Fp2, Fz, F8, T8). At posterior sites (P4, P8), reductions occurred only later in the week between the 4th and 7th nights of restriction. Both the immediate linear decline in arousal and precipitous drop later in the week were apparent at central sites (C4, Cz). Thus, frontal regions were affected immediately, while parietal regions showed maintenance of function until restriction was more severe. The P300 ERP component showed evidence of reduced attention by the 7th day of restriction (at Pz, P4). EEG and ERPs deficits were more robust in the right-hemisphere, which may reflect greater vulnerability to sleep loss in the non-dominant hemisphere.