Influences of disgust sensitivity on hemodynamic responses towards a disgust-inducing film clip.

The major goal of the present functional magnetic resonance imaging study was to investigate the influence of disgust sensitivity on hemodynamic responses during disgust induction. Fifteen subjects viewed three different film excerpts (duration: 135 s each) with disgust-evoking, threatening and neutral content. The films were presented in a block design with four repetitions of each condition. Afterwards, subjects gave affective ratings for the films and answered the questionnaire for the assessment of disgust sensitivity (QADS, []). The subjects' overall disgust sensitivity was positively related to their experienced disgust, as well as to their prefrontal cortex activation during the disgust condition. Further, there was a positive correlation between subjects' scores on the QADS subscale spoilage/decay and their amygdala activation (r=0.76). This was reasonable since the disgust film clip depicted a cockroach-invasion and the subscale spoilage/decay contains, among others, an item asking for disgust towards cockroaches. The study stresses, in accordance to previous studies, the importance of considering personality traits when studying affective responses in fMRI studies.     

Addressing the specificity of affective startle modulation: fear versus disgust.

Previous research is equivocal regarding whether startle reflex eyeblink is specifically sensitive to the emotion of fear, or is more generally influenced by the valence dimension of emotion. Thirty-five undergraduate participants (17 male) viewed 60 pictures from five affective categories (pleasant, neutral, fear, disgust-blood, and disgust-other). Bilateral eyeblink EMG responses to acoustic startle probes were assessed during 2/3 of picture presentations, and 1/3 of intertrial intervals. Left corrugator and levator EMG responses to no-startle pictures were also examined. Supporting an emotional valence model of affective startle modulation, the startle potentiation effect was not specific to fear materials. In fact, women, but not men, had larger startles during disgust compared with fear pictures. Both corrugator and levator EMG responses were greater to disgust than fear stimuli. These findings limit the generalizability of corrugator as an index of all negative emotions and extend evidence for the specificity of levator to disgust.     

Sympathetic and parasympathetic responses to a core disgust video clip as a function of disgust propensity and disgust sensitivity

It is generally assumed that disgust is accompanied by increased activation of the parasympathetic nervous system (PNS). However, empirical support for the role of PNS in disgust is scarce. This study tested whether (i) activation of the PNS is indeed involved in disgust and (ii) disgust-induced autonomic activation is especially pronounced in individuals with high disgust propensity or enhanced disgust sensitivity. Participants (N = 60) viewed a 5 min disgust-inducing video clip. Participants showed increased parasympathetic activity of both the cardiac and the digestive components of the autonomic nervous system (ANS), together with increased sympathetic activation of the cardiac system. ANS responses were independent of subjective disgust and individuals’ habitual disgust propensity or sensitivity. Results support the hypothesis that PNS activation is involved in disgust. The absence of a relationship between subjective and physiological indices of disgust indicates that both types of responses reflect independent phenomena.     

Sympathetic and parasympathetic responses to a core disgust video clip as a function of disgust propensity and disgust sensitivity

It is generally assumed that disgust is accompanied by increased activation of the parasympathetic nervous system (PNS). However, empirical support for the role of PNS in disgust is scarce. This study tested whether (i) activation of the PNS is indeed involved in disgust and (ii) disgust-induced autonomic activation is especially pronounced in individuals with high disgust propensity or enhanced disgust sensitivity. Participants (N=60) viewed a 5 min disgust-inducing video clip. Participants showed increased parasympathetic activity of both the cardiac and the digestive components of the autonomic nervous system (ANS), together with increased sympathetic activation of the cardiac system. ANS responses were independent of subjective disgust and individuals' habitual disgust propensity or sensitivity. Results support the hypothesis that PNS activation is involved in disgust. The absence of a relationship between subjective and physiological indices of disgust indicates that both types of responses reflect independent phenomena.     

Stimulus contrast and visual cortical lesions

Summary Intact animals can make fine orientation discriminations over a wide range of contrasts. After ablation of area 17 deficits in orientation discrimination are observed only at low contrast. The relevance of this finding for the design of sensitive ablation experiments is discussed.     

Anteromedial temporal lobe damage blocks startle modulation by fear and disgust

The acoustic startle reflex (ASR) is potentiated during negative emotion, but attenuated during positive emotional experience. The modulation of the ASR by fear depends critically on the amygdala. The authors investigated ASR modulation to fearful, disgusting, pleasant, and neutral stimuli in 12 patients with unilateral damage to the anteromedial temporal lobe including the amygdala (6 left, 6 right), 1 patient with bilateral temporal lobe damage including the amygdala, and 12 comparison participants. Both groups with unilateral damage, as well as the subject with bilateral damage, showed a complete lack of ASR potentiation to both fear and disgust stimuli. The findings suggest that potentiation of the ASR by disgust and fear depends on the integrity of the anteromedial temporal lobe.     

Hemodynamic responses of the amygdala, the orbitofrontal cortex and the visual cortex during a fear conditioning paradigm.

Functional magnetic resonance imaging (fMRI) studies consistently demonstrate an enhanced activation of the visual cortex in reaction to emotionally salient visual stimuli. This increase of activation is probably modulated by top-down processes, that are initiated in emotion processing structures, specifically the amygdala and the orbitofrontal cortex. In the present fMRI study, a differential fear conditioning paradigm was applied to investigate this assumed modulation. Hemodynamic responses towards a neutral visual stimulus (CS+) predicting an electrical stimulation (UCS) were compared with responses towards a neutral and unpaired stimulus (CS-). Thereby, particularly the time courses of neural responses were considered. Skin conductance measures were concurrently recorded. Our results show that the differentiation between CS+ and CS- within the amygdala and the extended visual cortex was accomplished during a late acquisition phase. In the orbitofrontal cortex the differentiation occurred at an earlier stage and was then sustained throughout acquisition. It is suggested that these altering activation patterns are reflecting different phases of learning, integrating the analyzed regions to varying degrees. Additionally, the results indicate that statistical analyses comprising a temporal variation of hemodynamic responses are more likely to detect amygdala activation.     

Endothelial function and hemodynamic responses during mental stress.

OBJECTIVE: The hemodynamic basis of blood pressure responses during psychological stress shows striking individual differences that share an interesting similarity with risk for cardiovascular disease. Factors accounting for these individual differences are poorly understood. The present study examined the relationship of vascular endothelial function to stress-induced hemodynamic responses. METHODS: Subjects were 40 healthy men and women, aged 25 to 44 years. Hemodynamic responses were assessed during exposure to a battery of four diverse laboratory stressors. Endothelium-dependent arterial dilation (EDAD) was measured by ultrasound imaging of the brachial artery in response to reactive hyperemia. RESULTS: High EDAD response was associated with lower resting systolic (p < .01) and diastolic blood pressure (p < .05). EDAD response was unrelated to blood pressure responses during stress. However, systemic vascular resistance responses during laboratory stress were significantly greater (p < .02) for individuals with low EDAD responses. CONCLUSIONS: Exaggerated systemic vascular resistance responses during stress may reflect endothelial dysfunction. This association may help explain the growing evidence of a relationship between stress hemodynamics and cardiovascular disease risk. The nature of this association is discussed in terms of a possible interplay between the sympathetic nervous system and the endothelium in regulation of vascular tone.     

Propensity and sensitivity measures of fear and disgust are differentially related to emotion-specific brain activation

Neuroimaging studies on individual differences in experiencing disgust and fear have indicated that disgust propensity and trait anxiety are able to moderate brain activity. The moderating role of disgust sensitivity and anxiety sensitivity has not been investigated thus far. Both sensitivity traits refer to the tendency of a person to perceive harmful consequences of experiencing fear and disgust. Eighteen female subjects viewed and subsequently rated pictures for the elicitation of disgust, fear and a neutral affective state. The viewing of the aversive pictures was associated with activation of visual processing areas, the amygdala, the insula and the orbitofrontal cortex (OFC). In the disgust condition, disgust propensity was positively correlated with activation of attention-related areas (parietal cortex, anterior cingulate cortex (ACC)) and brain regions involved in valence and arousal processing (OFC, insula). For the fear condition, we observed positive correlations between trait anxiety and activation of the ACC, the insula, and the OFC. Correlations between brain activity and sensitivity measures were exclusively negative and concerned areas crucial for emotion regulation, such as the medial and dorsolateral prefrontal cortex (MPFC, DLPFC). Thus, individuals high in disgust/anxiety sensitivity might have difficulties to successfully control the specific affective experience.     

Neuroticism and brain responses to anticipatory fear

Personality is known to influence cognitive and affective functioning as well as the risk of psychiatric disorders. Exploration of the neurobiological correlates of personality traits has the potential to enhance understanding of their significance in development of related psychopathological states. The authors examined the association between individual differences in neuroticism and brain activity in response to threat of electric shocks. Fourteen right-handed healthy men underwent functional MRI during a 5-min experiment that involved repeated presentations of two 30-s alternating conditions. In 1 of these conditions, subjects were told to expect mild but painful electric shocks; there was no possibility of receiving shocks in the other condition. The results revealed that neuroticism correlated positively with the ratings of fear of shock and negatively (indicating suppression) with brain activity from safe to shock conditions in the anterior and posterior cingulate, superior/middle temporal gyrus extending to the hippocampus, precuneus, putamen, thalamus, and middle occipital gyrus. The observations support recent psychophysiological research that has demonstrated reduced processing of pain in subjects with higher levels of neuroticism, especially the anxiety component of this trait.     

"Stimulus generalization" between differentiated visual, auditory, and central stimuli.

Cats were trained to discriminate between two different repetition rates of flicker and of click. Both approach-approach and avoidance-avoidance discriminations were used. After substantial overtraining, transfer of frequency discrimination was initiated to stimulation of the reticular formation using bursts of electrical pulses at the same two repetition rates. Significant levels of discriminated performance were obtained in all cats very quickly, indicating good cross-modal transfer between the peripheral discriminanda and the central stimuli. The literature on stimulus generalization and cross-modal transfer is reviewed and the findings of this experiment are discussed in that context. Certain conditions are defined which, if satisfied, justify the interpretation that stimulus generalization or rapid cross-modal transfer indicate that facilitation of subsequent tasks in a training sequence can be attributed to mediation by a specific neuronal mechanism established by training on a previous task. The present experiment was designed in view of such criteria. The evidence of good cross-modal transfer is interpreted to mean that brain mechanisms storing memories about discriminations between visual or auditory stimuli with different repetition rates can be effectively activated by gross electrical stimuli at the same repetition rates. Conflict trials were then carried out in which flicker or click at either frequency was contradicted by concurrent RF stimuli at the other frequency. As the current level of RF stimuli was parametrically increased, it was found that the central stimuli achieved almost complete control over the behavioral outcome in most cases. Concurrent transfer of training, using a counterbalanced training sequence, was then carried out to stimulation of the visual cortex, lateral geniculate, medial geniculate, and the intralaminar nuclei of the thalamus. In each case, rapid transfer was displayed by at least one animal. Once performance to brain stimulation at a given repition rate was established, little change was observed when the fine structure of the stimulus was altered by changing parameters of the stimulus burst. These findings are interpreted as providing support for a statistical theory of memory, since they constitute evidence that previously learned discriminative behavior can readily be elicited by compelling large ensembles of neurons in various brain regions to discharge with particular temporal patterns. It is difficult to reconcile these results with theories which postulate that learning establishes new synaptic pathways in which discharge must occur for memories to be retrieved.     

Pattern-motion responses in human visual cortex.

Physiological models of visual motion processing posit that 'pattern-motion cells' represent the direction of moving objects independent of their particular spatial pattern. We performed fMRI experiments to identify neuronal activity in the human brain selective for pattern motion. A protocol using adaptation to moving 'plaid' stimuli allowed us to separate pattern-motion responses from other types of motion-related activity within the same brain structures, and revealed strong pattern-motion selectivity in human visual area MT+. Reducing the perceptual coherence of the plaids yielded a corresponding decrease in pattern-motion responsivity, providing evidence that percepts of coherent motion are closely linked to the activity of pattern-motion cells in human MT+.     

Stimulus specificity and temporal dynamics of working memory for visual motion

When asked to compare two moving stimuli separated by a delay, observers must not only identify stimulus direction but also store it in memory. We examined the properties of this storage mechanism in two macaque monkeys by sequentially presenting two random-dot stimuli, sample and test, in opposite hemifields and introducing a random-motion mask during the delay. The mask interfered with performance only at the precise location of the test, 100-200 ms after the start of the delay, and when its size and speed matched those of the remembered sample. This selective interference suggests that the representation of the motion stimulus in memory preserves its direction, speed, and size and is most fragile shortly after the completion of the encoding phase of the task. This precise preservation of sensory attributes of the motion stimulus suggests that the neural mechanisms involved in the processing of visual motion may also be involved in its storage.     

Stimulus dynamics increase the self-administration of compound visual and auditory stimuli

Animals will acquire an operant task using sensory stimuli as a primary reinforcer. Many operant tasks use sensory stimuli as cues that are paired with other primary reinforcers. Recent studies have called attention to this potential confound, but there has not been a parametric assessment of the effect of stimulus variability on operant responding. We found that stimulus variability increased the amount of operant responding exhibited by mice, a phenomenon observed under both fixed- and progressive-ratio schedules.     

Stimulus rise time, intensity and the elicitation of unconditioned cardiac and electrodermal responses.

In recent discussions on the differentiation of orienting, startle and defense responses, the importance of stimulus rise time for the elicitation of different cardiac response patterns was re-emphasized. Especially, it has been claimed that phasic accelerative heart rate (HR) responses-interpreted as indicators of startle-might not only be evoked by auditory stimuli with instantaneous rise times and high intensities, but also by low to moderate stimulus intensities with sudden onsets. The present study examined this question by manipulating rise time (instantaneous vs. 50 ms) and intensity (60 vs. 95 dB). Subjects (N = 120) were randomly assigned to one of the four independent groups. They performed a habituation experiment in which 12 tones of 1000 Hz with a constant interstimulus interval of 90 s were presented. On trial 13, a change in rise time was introduced by reversing the rise time condition in each group (i.e., from instantaneous to 50 ms and vice versa). Examination of HR changes across 4 poststimulus seconds, of maximal HR deceleration and acceleration, as well as examination of magnitude of skin conductance responses (SCRs) indicated clear intensity effects. Rise time, on the other hand, had no effects on HR and SC that could be interpreted as indicative of startle. Thus, it could neither be observed that instantaneous rise time led to stronger accelerative HR responses nor that the combination of instantaneous rise time and high intensity elicited anything but a dominant accelerative response pattern. These findings were also obtained when the first four trials were analyzed separately. As a consequence of stimulus change, larger SCRs as well as larger decelerative HR responses were observed without, however, being affected by the direction of the change in rise time. In sum, the present study suggests that the role attributed to rise time with respect to eliciting qualitatively different cardiac response patterns has been exaggerated. The consequences for the differentiation of different unconditioned responses are briefly addressed.     

Skin conductance responses to visual sexual stimuli.

Previous research showed that the asymmetrical direction of bilateral skin conductance responses (SCRs) remains constant regardless of task (with larger left SCRs in men and larger right SCRs in women). However, SCRs are controlled ipsilaterally by structures also associated with sexual arousal, hence it could be expected that larger right SCRs are specifically elicited by sexual stimuli. In order to test the two competing hypotheses, left and right SCR magnitude to three stimulus categories (sexually explicit, sexually non-explicit and neutral) were compared in 54 subjects (27 females). The direction of the asymmetry remained constant across stimulus types, however, unexpected sex differences occurred, as males had larger right SCRs and there was no lateralization in females. Interestingly, this interaction disappeared after controlling for indicators of subjective sexual arousal, suggesting that a specific (not previously hypothesized) processing of sexual information could take place.