Affective modulation of autonomic reactions to noxious stimulation.

Research suggests that emotion modulates spinal nociception and pain; however, there is limited evidence that other objective, nociceptive reactions are modulated. This study examined the impact of affective picture-viewing on autonomic reactions (skin conductance response, heart rate acceleration) resulting from noxious electric stimulations to the sural nerve. Pictures varying in affective valence (unpleasant, neutral, pleasant) were presented during which noxious stimulations were delivered. Skin conductance response and short-latency heart rate acceleration following each stimulation was calculated and averaged by picture valence. Results suggested that autonomic reactions were modulated in parallel. Specifically, reactions were smaller during pleasant pictures than unpleasant pictures, although unpleasant pictures did not result in significant facilitation relative to neutral pictures. The valence linear trend explained 26% of the variance in the multivariate combination of the reactions, suggesting emotion does modulate autonomic reactions to nociception. These results suggest that SCR and HR acceleration are outcomes that can be assessed together with NFR and pain report during picture-viewing to study affective modulation of spinal (NFR), supraspinal (SCR, HR acceleration), and subjective (pain report) nociceptive reactions.     

Examining emotional modulation of pain and spinal nociception in Native Americans: A preliminary investigation

Pain problems are more prevalent in Native Americans than in any other group in the U.S., and this might result from group differences in pain modulation. This study was designed to examine emotional modulation of pain and spinal nociception in healthy, pain-free Native Americans (n = 21) relative to non-Hispanic Whites (n = 20). To assess emotional modulation of pain and the nociceptive flexion reflex (NFR, a physiological measure of spinal nociception), participants underwent a well-validated emotional picture-viewing paradigm during which suprathreshold pain stimuli were delivered to the ankle. Compared to Whites, Native Americans reported less pleasure to erotic pictures and failed to show corrugator reactivity to mutilation pictures. Unlike Whites, Native Americans only evidenced pain inhibition in response to erotica, but no pain facilitation (disinhibition) to mutilation pictures. Emotional modulation of NFR was similar in both groups. These preliminary findings suggest that Native Americans failed to disinhibit pain, perhaps due to over-activation of pain inhibitory mechanisms. Chronic over-activation of this system could ultimately exhaust it, thus putting Native Americans at future risk for chronic pain.     

Affective modulation of nociception at spinal and supraspinal levels

This study was designed to examine the effect of emotion on the nociceptive flexion reflex and pain ratings. To do so, 28 participants viewed pictures varying in emotional valence (unpleasant, neutral, pleasant) and electric stimulations were delivered during and in between pictures. Biceps femoris EMG resulting from the stimulations was used to quantify the nociceptive flexion reflex (spinal nociception), and pain ratings to the stimulations were used as an evaluative measure of supraspinal nociception. Manipulation checks suggested that pictures effectively manipulated emotion. Moreover, nociceptive flexion reflex magnitudes and pain ratings were modulated in a parallel manner. Specifically, viewing unpleasant pictures enhanced the nociceptive flexion reflex and pain, whereas viewing pleasant pictures inhibited the reflex and pain. Analyses suggested that emotional valence, but not arousal, mediated the effects of pictures.     

Temporal course of emotional startle modulation in schizophrenia patients.

The temporal course of startle reflex modulation to emotional pictures was investigated in 49 relatively asymptomatic schizophrenia outpatients and 46 normal controls. Participants viewed pleasant, neutral and unpleasant pictures, which were presented for 6 s and acoustic startle probes were delivered at five different times after picture onset. Replicating previous findings schizophrenia patients showed the same affective modulation of the startle reflex as healthy controls when probes were presented later during the picture-viewing period (3800 ms). For the early probe times (300 and 800 ms), affective pictures proved to be the effective prepulse stimuli resulting in a clear Prepulse inhibition (PPI) effect in both groups. In contrast to previous findings, the PPI of startle response was not stronger during processing emotional stimuli relative to neutral stimuli. For control subjects, blink reflexes were larger for unpleasant pictures compared with neutral and pleasant pictures, representing an early activation of motivational systems. Schizophrenia patients on the other hand, did not show this early affective modulation of the acoustic startle reflex.     

The psychophysiology of social anxiety: Emotional modulation of the startle reflex during socially-relevant and -irrelevant pictures

The present study examined affective processes of social anxiety (SA) through emotional modulation of the startle reflex. Eighty-four high and low trait socially anxious undergraduates viewed socially-relevant and socially-irrelevant pleasant, neutral, and unpleasant pictures, and acoustic startle probes were presented during pictures and the inter-trial interval. Startle was potentiated during unpleasant compared to pleasant stimuli, but this valence modulation did not reliably vary between groups or socially-relevant and -irrelevant stimuli. However, when participants were categorized based on public-speaking fears rather than general SA symptoms, the high fear group demonstrated reliable valence modulation, whereas the low fear group did not. These findings are interpreted within the context of the broader literature suggesting that the specificity of fear in SA may influence psychophysiological reactivity.     

Affective startle modulation in anticipation and perception

Startle modulation was investigated as participants first anticipated and then viewed affective pictures in order to determine whether affective modulation of the startle reflex is similar in these different task contexts. During a 6-s anticipation period, a neutral light cue signaled whether the upcoming picture would portray snakes, erotica, or household objects; at the end of the anticipatory period, a picture in the signaled category was viewed for 6 s. Male participants highly fearful of snakes were recruited to maximize emotional arousal during anticipation and perception. Results indicated that the startle reflex was potentiated when anticipating either unpleasant (phobic) or pleasant (erotic) pictures, compared to neutral stimuli, whereas during perception, reflexes were potentiated when viewing unpleasant stimuli, and reduced when viewing pleasant pictures. The startle reflex is modulated by hedonic valence in picture perception, and by emotional arousal in a task context involving picture anticipation.     

Emotional modulation of pain-related evoked potentials

To investigate whether cortical processing of trigeminal nociception is modulated by emotion, the N2 and P2 components of the pain-related evoked potential (PREP) were recorded in response to noxious stimulation of the supraorbital nerve while participants viewed neutral, pleasant and unpleasant pictures. The nerve was stimulated at 125% of pain threshold via a nociceptive-specific concentric electrode to selectively activate A-delta pain fibres. The N2 and P2 pain-related evoked potentials were similarly influenced by emotional priming: the amplitude of both potentials decreased monotonically from viewing neutral to pleasant to unpleasant pictures. These findings show that cortical processing of trigeminal nociception is modulated by emotion. We explain our findings in terms of the effects of picture viewing on attention.     

Do sex hormones influence emotional modulation of pain and nociception in healthy women?

Sex hormones may contribute to inter- and intra-individual differences in pain by influencing emotional modulation of pain and nociception. To study this, a well-validated picture-viewing paradigm was used to assess emotional modulation of pain and the nociceptive flexion reflex (NFR; physiologic measure of nociception) during mid-follicular, ovulatory, and late-luteal phases of the menstrual cycle in healthy normally cycling women (n = 40). Salivary estradiol, progesterone, and testosterone were assessed at each testing session. Emotional modulation of pain/NFR did not differ across menstrual phases, but low estradiol was associated with weaker emotional modulation of NFR (during all phases) and emotional modulation of pain (ovulatory and late-luteal phases). Given evidence that a failure to emotionally modulate pain might be a risk factor for chronic pain, low estradiol may promote chronic pain via this mechanism. However, future research is needed to extend these findings to women with disturbances of pain, emotion, and/or sex hormones.     

Intentional modulation of emotional responding to unpleasant pictures: an ERP study

Intentionally altering responses to unpleasant stimuli affects physiological and hemodynamic activity associated with emotional and cognitive processing. In the present experiment, we measured the late-positive potential (LPP) of the visually evoked event-related brain potential to examine the effects of intentional emotion modulation on electrophysiological correlates of emotional and cognitive processing. Seventeen participants received instructions to view, suppress, and enhance emotional responses to unpleasant stimuli. Results revealed significantly decreased electrophysiological activity during suppression of emotional responses beginning around 250 ms poststimulus and lasting several hundred milliseconds. These data suggest that ERPs are sensitive to emotion modulation/regulation processes.     

Affective modulation and prepulse inhibition of startle among undergraduates high and low in behavioral inhibition and approach

Valence modulation and prepulse inhibition of startle were examined among 80 undergraduates scoring in the upper and lower quartiles of self-report measures of behavioral inhibition (BIS) and behavioral approach (BAS). Participants viewed a series of pleasant, neutral, and unpleasant pictures. Acoustic startle probes (102 dB) were presented during most pictures and during intertrial intervals, and a prepulse (120-ms SOA) preceded half of the probes. Valence modulation on no-prepulse trials was greater among high-BAS than low-BAS participants. Consistent with theory regarding behavioral approach, post hoc tests demonstrated robust inhibition during pleasant versus neutral pictures among high-BAS participants, but not low-BAS participants. Valence modulation was reliable among high-BIS but not low-BIS participants, but the group difference was not significant. Contrary to our prediction, prepulse inhibition tended to be greater among high-BAS than low-BAS participants. The present data call attention to the role of individual differences in pleasant affective experience in startle modification.     

Revisiting the James versus Cannon debate on emotion: startle and autonomic modulation in patients with spinal cord injuries

James' hypothesis that impaired peripheral physiology in patients with spinal cord injuries (SCI) impairs emotional processing, as manifested in the modulation of physiological responses and in the subjective component of emotions, was examined in the present study. A pilot study confirmed the utility of Lang's picture viewing paradigm in a group of 78 students using the Spanish norms of the International Affective Picture System. In the main study, 19 patients with SCI and 19 well controls matched for sex, age and education were examined. Results showed: (1) no differences between SCI and control participants in the valence and arousal ratings of the pictures; (2) similar heart rate modulation in both groups, i.e. the unpleasant pictures produced greater deceleration than the pleasant ones; and (3) no decrease in emotional experience in the SCI group compared with the control group. The implications of the results for the James versus Cannon controversy on the theory of emotions are discussed.     

Neural response to emotional pictures is unaffected by concurrent task difficulty: an event-related potential study

The late positive potential (LPP) is an event-related potential that is enhanced when viewing arousing (pleasant and unpleasant) pictures compared to neutral pictures. The affective modulation of the LPP is believed to reflect the increased attention to, and perceptual processing of, emotional stimuli. The present study examined whether concurrent task difficulty (performing mathematics) would modulate the LPP while participants viewed emotionally arousing stimuli. Results indicated that the LPP was larger following pleasant and unpleasant stimuli than it was following neutral stimuli; moreover, the magnitude of this increase was not influenced by concurrent task difficulty. This finding suggests that the affective modulation of neural activity during picture viewing is relatively automatic and is insusceptible to competing task demands. Results are further discussed in terms of the LPP's role in motivated attention and implications for research on emotion regulation.     

The effects of affective picture stimuli on blink modulation in adults and children

Two experiments examined blink modulation during viewing of pleasant, neutral and unpleasant picture stimuli in non-selected adults (N = 21) and children (N = 60) and children with anxiety disorders (N = 12). Blink reflexes were elicited by a white noise probe of 105 dB at lead stimulus intervals of 60, 240, 3500, and 5000 ms and during intertrial intervals. Blink modulation during unpleasant pictures was significantly different from blink modulation during neutral pictures at the 60 ms lead interval in children whereas adults showed no significant differences. Picture content had no differential effect on the extent of blink modulation for adults or children at the 240 ms lead interval. At the long lead intervals, blink modulation during unpleasant and pleasant pictures was significantly larger than during neutral pictures in adults. Picture valence did not differentially affect the extent of blink modulation at long lead intervals in children. Comparing the extent of blink modulation in anxious and non-selected children, blinks were significantly modulated during unpleasant pictures at the 60 ms lead interval for both groups. However, the extent of blink modulation was larger overall at this very short lead interval in anxious children. Children did not differ at other lead intervals.     

The effects of contextual threat and anxiety on affective startle modulation

The startle reflex is attenuated and potentiated when participants are viewing pleasant and unpleasant images, respectively. Research demonstrates that threatening contexts also potentiate startle, but it remains unclear how a threatening context might impact startle modulation to emotional images, especially as a function of trait anxiety. The present study measured startle reactivity while 43 participants viewed pleasant, unpleasant, and neutral images across conditions of threat-of-shock and safety (i.e., no shock). Compared to neutral images, startle was potentiated during unpleasant images and attenuated during pleasant images. Threat-of-shock potentiated startle during all picture types, suggesting that threat-of-shock broadly sensitized the defensive system but did not change affective modulation of startle. Lastly, higher levels of trait anxiety were associated with less startle potentiation during unpleasant images across both conditions—a finding in line with previous research demonstrating deficient threat mobilization in response to unpleasant stimuli among highly anxious individuals.     

Loss of emotional experience after traumatic brain injury: findings with the startle probe procedure

The authors used affective modulation of the eyeblink startle response to examine the impact of traumatic brain injury (TBI) on emotional reactions to pictures. Participants were 13 individuals with severe TBI and 24 controls. Participants were presented with pictures that differed in affective valence (e.g., mutilated bodies, erotic couples, and household objects) while the eyeblink startle response to an acoustic probe was measured. Startle amplitude was used to assess valence of emotional response, and startle latency was used to index interest in the pictures. Subjective ratings of the affect and arousal elicited by the various pictures were also obtained. TBI impaired startle potentiation to unpleasant pictures but not startle attenuation to pleasant pictures. Further, subjective ratings indicated that TBI participants found unpleasant pictures less arousing than did controls. The results are consistent with recent evidence of differential impairment in negative versus positive emotions after TBI and are discussed in relation to 2 competing explanations of startle modulation.     

Modulation of spinal reflexes: Arousal, pleasure, action

The human startle reflex is reliably modulated by the affective valence of foreground pictures, with larger reflexes elicited when viewing unpleasant relative to pleasant scenes. If this modulation is due to priming of the defensive startle reflex by an aversive foreground, a different pattern should occur for a reflex that is not inherently defensive in nature. In the current study, affective modulation was investigated using the spinal tendinous (T) reflex, which is well documented as sensitive to differences in arousal and is involved in actions that are both appetitively and defensively motivated. As such, T reflexes elicited during unpleasant pictures were not expected to be augmented relative to those elicited in the context of pleasant pictures. Results showed that T reflexes were facilitated during processing of arousing stimuli – either pleasant or unpleasant relative to low-arousal neutral materials. These effects of emotional stimuli on T-reflex amplitude are consistent with the hypothesis that motivational priming underlies affective reflex modulation.     

Arousal and valence effects on event-related P3a and P3b during emotional categorization

Due to the adaptive value of emotional situations, categorizing along the valence dimension may be supported by critical brain functions. The present study examined emotion–cognition relationships by focusing on the influence of an emotional categorization task on the cognitive processing induced by an oddball-like paradigm. Event-related potentials (ERPs) were recorded from subjects explicitly asked to categorize along the valence dimension (unpleasant, neutral or pleasant) deviant target pictures embedded in a train of standard stimuli. Late positivities evoked in response to the target pictures were decomposed into a P3a and a P3b and topographical differences were observed according to the valence content of the stimuli. P3a showed enhanced amplitudes at posterior sites in response to unpleasant pictures as compared to both neutral and pleasant pictures. This effect is interpreted as a negativity bias related to attentional processing. The P3b component was sensitive to the arousal value of the stimulation, with higher amplitudes at several posterior sites for both types of emotional pictures. Moreover, unpleasant pictures evoked smaller amplitudes than pleasant ones at fronto-central sites. Thus, the context updating process may be differentially modulated by the affective arousal and valence of the stimulus. The present study supports the assumption that, during an emotional categorization, the emotional content of the stimulus may modulate the reorientation of attention and the subsequent updating process in a specific way.     

Affective modulation of eyeblink reactions to noxious sural nerve stimulation: a supraspinal measure of nociceptive reactivity?

Research suggests affective picture-viewing modulates subjective and physiological reactions to noxious stimulation (pain report, heart rate acceleration, skin conductance response, nociceptive flexion reflex). Because the nociceptive flexion reflex (a spinal reflex) is modulated by picture-viewing, this suggests affective processes are able to modulate afferent nociception at spinal levels. This highlights the importance of assessing nociceptive reactivity from physiological measures mediated at different levels of the neuraxis (spinal vs. supraspinal) to help elucidate the mechanisms associated with pain regulation. The present study examined whether affective pictures modulate eyeblink reactions (a supraspinal reflex) to noxious stimulation. Healthy men and women (N=23) were recruited from the psychology subject pool to participate. Pictures (attack, loss, neutral, food, erotica) that manipulated affective valence and arousal were presented and noxious electrodermal stimulations were delivered to the sural nerve. Picture duration (500-ms vs. 6-s) was also manipulated, balanced across picture content. Results suggested affective valence and arousal contributed to the modulation of eyeblinks. Eyeblinks were larger during highly arousing unpleasant pictures (attack) than highly arousing pleasant pictures (erotica), but low arousal pictures (loss, food) did not lead to significant modulation. Affective modulation was independent of picture duration or the perceived painfulness of noxious stimulation. This study suggests eyeblink reactions can serve as a supraspinal outcome in procedures used to study affective modulation of pain and nociception.     

Affective modulation of eyeblink reactions to noxious sural nerve stimulation: A supraspinal measure of nociceptive reactivity?

Research suggests affective picture-viewing modulates subjective and physiological reactions to noxious stimulation (pain report, heart rate acceleration, skin conductance response, nociceptive flexion reflex). Because the nociceptive flexion reflex (a spinal reflex) is modulated by picture-viewing, this suggests affective processes are able to modulate afferent nociception at spinal levels. This highlights the importance of assessing nociceptive reactivity from physiological measures mediated at different levels of the neuraxis (spinal vs. supraspinal) to help elucidate the mechanisms associated with pain regulation. The present study examined whether affective pictures modulate eyeblink reactions (a supraspinal reflex) to noxious stimulation. Healthy men and women (N = 23) were recruited from the psychology subject pool to participate. Pictures (attack, loss, neutral, food, erotica) that manipulated affective valence and arousal were presented and noxious electrodermal stimulations were delivered to the sural nerve. Picture duration (500-ms vs. 6-s) was also manipulated, balanced across picture content. Results suggested affective valence and arousal contributed to the modulation of eyeblinks. Eyeblinks were larger during highly arousing unpleasant pictures (attack) than highly arousing pleasant pictures (erotica), but low arousal pictures (loss, food) did not lead to significant modulation. Affective modulation was independent of picture duration or the perceived painfulness of noxious stimulation. This study suggests eyeblink reactions can serve as a supraspinal outcome in procedures used to study affective modulation of pain and nociception.     

State anxiety and affective physiology: effects of sustained exposure to affective pictures

Effects of sustained exposure to emotional stimuli on affective reactions and their recovery were examined to determine whether increasing exposure to a specific emotional content (e.g., unpleasant) cumulatively affects physiological responses; and whether motivational activation persists following sustained exposure. Participants viewed pleasant, neutral, and unpleasant IAPS pictures, presented in blocks separated by an inter-block interval. With increasing exposure to unpleasant pictures, startle magnitude showed greater potentiation, and corrugator EMG activity increased. Both affective startle and corrugator modulation persisted following exposure to unpleasant pictures. The cumulative effects of sustained exposure to unpleasant pictures were enhanced for those reporting higher state anxiety, consistent with the hypothesis that sustained aversive exposure leads to increased defensive activation. These findings suggest sustained exposure to unpleasant pictures may induce a short-term mood state, and may be a useful paradigm to study individuals who vary in symptoms of anxiety.