Differential effects of glucose on modulation of emotional and nonemotional spatial memory tasks

Research examining the memory-enhancing effects of glucose in humans has been limited to mnemonic tasks lacking affective components, even though glucose may be a mechanism for emotioninduced memory enhancement. This limitation does not permit analysis of interactions between the enhancing properties of emotional stimuli and glucose. Participants were administered either glucose or saccharin 15 min prior to completing a neutral or emotional spatial memory task. Performance under three glycemic conditions (100 mg/kg or 50 g glucose, or placebo) for the two sets of emotional stimuli revealed a significant interaction. Both 100-mg/kg and 50-g doses of glucose resulted in impaired performance for emotional stimuli. For neutral stimuli, a 100-mg/kg dose enhanced memory, whereas a 50-g dose showed no effect. Results indicate that the enhancing effects of emotional stimuli may be attenuated by the consumption of glucose and suggest that recent food consumption should be considered in paradigms examining memory.     

Effects of pre-learning stress on memory for neutral, positive and negative words: Different roles of cortisol and autonomic arousal

Stress can have enhancing or impairing effects on memory. Here, we addressed the effect of pre-learning stress on subsequent memory and asked whether neutral and emotionally valent information are differentially affected by specific stress components, autonomic arousal and stress-induced cortisol. Ninety-six healthy men and women underwent either a stressor (modified cold pressor test) or a control warm water exposure. During stress, participants showed comparable autonomic arousal (heart rate, blood pressure), while 60 percent showed an increase of cortisol (responders vs. 40 percent non-responders). Ten minutes after the cold pressor test neutral, positive and negative words were presented. Free recall was tested 1 and 24 h later. Overall, positive and negative words were better recalled than neutral words. Stress enhanced the recall of neutral words independently of cortisol response. In contrast, the free recall of negative words was enhanced in cortisol responders in the 1-h but not 24-h test which might suggest different effects of cortisol on consolidation and reconsolidation processes. Recall for positive words was unaffected by stress-induced cortisol. To summarize, (i) pre-learning stress can enhance memory for neutral words independently of cortisol and (ii) stress effects on memory for negative words appear to rely on stress-induced cortisol elevations, the absence of this effect for positive words might be at least partly due to differences in arousal evoked by positive vs. negative words.     

Immediate and prolonged effects of cortisol, but not propranolol, on memory retrieval in healthy young men

BackgroundWhile acute cortisol administration has been found to impair retrieval of emotional memories in healthy subjects, the duration of this memory impairment is still unknown. Propranolol, on the other hand, may impair the reconsolidation of emotional memories during reactivation, although human studies examining such effects are scarce. The present investigation was therefore undertaken to examine the immediate and prolonged effects of a single administered dose of cortisol or propranolol on memory retrieval in a double-blind placebo controlled design.MethodsEighty-five healthy male participants were asked to retrieve previously learned emotional and neutral information after ingestion of 35 mg cortisol, 80 mg propranolol or placebo. After a washout period of 1 week, recall was again tested.ResultsMemory retrieval of neutral and emotional information was impaired by a single dose of cortisol compared to placebo. The memory impairment due to cortisol remained, even after a washout period of 1 week. No immediate or prolonged effects of propranolol on memory retrieval were found, despite significant reductions in sympathetic arousal.ConclusionsThese results lend support to the hypothesis that cortisol is able to attenuate (emotional) memory recall in men over longer time spans and may therefore augment the treatment of disorders like post-traumatic stress disorder and phobias, but do not clarify the mechanism(s) through which propranolol exerts its therapeutic effects.     

Emotional distraction in boys with ADHD: Neural and behavioral correlates

Although, in everyday life, patients with attention deficit hyperactivity disorder (ADHD) are frequently distracted by goal-irrelevant affective stimuli, little is known about the neural and behavioral substrates underlying this emotional distractibility. Because some of the most important brain responses associated with the sudden onset of an emotional distracter are characterized by their early latency onset and short duration, we addressed this issue by using a temporally agile neural signal capable of detecting and distinguishing them. Specifically, scalp event-related potentials (ERPs) were recorded while 20 boys with ADHD combined type and 20 healthy comparison subjects performed a digit categorization task during the presentation of three types of irrelevant, distracting stimuli: arousing negative (A−), neutral (N) and arousing positive (A+). Behavioral data showed that emotional distracters (both A− and A+) were associated with longer reaction times than neutral ones in the ADHD group, whereas no differences were found in the control group. ERP data revealed that, compared with control subjects, boys with ADHD showed larger anterior N2 amplitudes for emotional than for neutral distracters. Furthermore, regression analyses between ERP data and subjects’ emotional ratings of distracting stimuli showed that only in the ADHD group, emotional arousal (ranging from calming to arousing) was associated with anterior N2: its amplitude increased as the arousal content of the visual distracter increased. These results suggest that boys with ADHD are more vulnerable to the distracting effects of irrelevant emotional stimuli than control subjects. The present study provides first data on the neural substrates underlying emotional distractibility in ADHD.     

The effects of emotional stimuli on target detection: indirect and direct resource costs

The present study was designed to explore the performance costs of negative emotional stimuli in a vigilance task. Forty participants (20 women) performed a vigilance task in two conditions: one with task-irrelevant negative-arousing pictures and one with task-irrelevant neutral pictures. In addition to performance, we measured subjective state (energetic arousal, tense arousal, task-related and task-unrelated thoughts) and frontal cerebral activity with near infrared spectroscopy. Overall performance in the negative picture condition was lower than in the neutral picture condition and the negative picture condition had elevated levels of energetic arousal, tense arousal and task-related thoughts. Moreover, there was a significant relationship between the impact of the negative pictures on tense arousal and task-related thoughts and the impact of the negative pictures on performance (in comparison to the neutral picture stimuli task). These results provide support for indirect cost models of negative emotional stimuli on target detection performance.     

Films for eliciting emotional states in children

Standardized sets of films have been shown to be effective for eliciting emotional states in adults, but no comparable validated stimuli are available for children. We therefore examined the effects of three pre-selected film clips each of 3-min duration in eliciting a pleasant, neutral and unpleasant emotional state in 297 children aged between 6 and 12 years. After the films were presented on a video projector, affective ratings were obtained with the Self-Assessment-Manikin on the emotional dimensions of valence and arousal. Increasing pleasure ratings were observed from the unpleasant to the neutral to the pleasant film. Associated arousal ratings were stronger for the unpleasant and pleasant films compared to the neutral film. Overall, results showed successful elicitation of targeted emotional states only marginally influenced by age, gender or prior experience with the films. The use of these films is therefore suggested for future studies on emotions in children.     

Electrophysiological differences in the processing of affective information in words and pictures

It is generally assumed that affective picture viewing is related to higher levels of physiological arousal than is the reading of emotional words. However, this assertion is based mainly on studies in which the processing of either words or pictures has been investigated under heterogenic conditions. Positive, negative, relaxing, neutral, and background (stimulus fragments) words and pictures were presented to subjects in two experiments under equivalent experimental conditions. In Experiment 1, neutral words elicited an enhanced late positive component (LPC) that was associated with an increased difficulty in discriminating neutral from background stimuli. In Experiment 2, high-arousing pictures elicited an enhanced early negativity and LPC that were related to a facilitated processing for these stimuli. Thus, it seems that under some circumstances, the processing of affective information captures attention only with more biologically relevant stimuli. Also, these data might be better interpreted on the basis of those models that postulate a different access to affective information for words and pictures.     

Emotion and Motor Control: Movement Attributes Following Affective Picture Processing

The authors investigated the impact of emotion on the performance of a square-tracing task after participants (N = 40) were exposed to pleasant (P), unpleasant (U), and neutral (N) pictures. Physiological and self-report measures indexed affective valence and arousal. In Experiment 1, greater error followed exposure to 4 consecutive U images than exposure to 4 consecutive P images. Speed of performance did not vary as a function of valence. In Experiment 2, participants viewed 1 slide per trial within a modified exposure protocol. Speed of performance varied as a function of valence; faster performance followed U relative to P stimuli. Accuracy of performance did not vary between conditions. Corresponding self-report and physiological measures generally corroborated previous evidence. Findings collectively indicated that the length of exposure to affective stimuli mediates speed and accuracy of motor performance; compared with P stimuli, U stimuli led to either increased error (short exposure) or increased speed (multiple exposures). The authors conclude that brief and extended exposures to affective pictures have direct behavioral consequences, and they discuss the implications of that finding.     

Emotion and motor control: movement attributes following affective picture processing

The authors investigated the impact of emotion on the performance of a square-tracing task after participants (N = 40) were exposed to pleasant (P), unpleasant (U), and neutral (N) pictures. Physiological and self-report measures indexed affective valence and arousal. In Experiment 1, greater error followed exposure to 4 consecutive U images than exposure to 4 consecutive P images. Speed of performance did not vary as a function of valence. In Experiment 2, participants viewed 1 slide per trial within a modified exposure protocol. Speed of performance varied as a function of valence; faster performance followed U relative to P stimuli. Accuracy of performance did not vary between conditions. Corresponding self-report and physiological measures generally corroborated previous evidence. Findings collectively indicated that the length of exposure to affective stimuli mediates speed and accuracy of motor performance; compared with P stimuli, U stimuli led to either increased error (short exposure) or increased speed (multiple exposures). The authors conclude that brief and extended exposures to affective pictures have direct behavioral consequences, and they discuss the implications of that finding.     

Impulsivity,neuroticism, and caffeine: Do they have additive effects on arousal?

The personality dimensions of impulsivity and neuroticism have been linked to differences in basal arousal. The hypothesis tested was whether these personality variables and caffeine have additive effects on arousal. All subjects received three paired-associate trials on each of two neutral control lists, two lists with semantically similar stimuli, and two lists with acoustically similar stimuli. Half of the subjects received caffeine and half placebo. Although significant interactions with personality and drug condition were obtained, the ordering of the conditions was inconsistent with the assumption that the arousal performance curve is single peaked. Further, S. Schwartz's (Journal of Research in Personality, 1975, 9, 217–225) hypothesis that in paired-associate learning high arousal and low arousal subjects process semantic and physical information differentially was not supported. The general issue of how to determine whether individual differences in performance are caused by differences in arousal is discussed.     

Emotional modulation of attention affects time perception: Evidence from event-related potentials

Emotional effects on human time perception are generally attributed to arousal speeding up or slowing down the internal clock. The aim of the present study is to investigate the less frequently considered role of attention as an alternative mediator of these effects with the help of event-related potentials (ERPs). Participants produced short intervals (0.9, 1.5, 2.7, and 3.3 s) while viewing high arousal images with pleasant and unpleasant contents in comparison to neutral images. Behavioral results revealed that durations were overproduced for the 0.9 s interval whereas, for 2.7 and 3.3 s intervals, underproduction was observed. The effect of affective valence was present for the shorter durations and decreased as the target intervals became longer. More specifically, the durations for unpleasant images were less overproduced in the 0.9 s intervals, and for the 1.5 s trials, durations for unpleasant images were slightly underproduced, compared to pleasant images, which were overproduced. The analysis of different ERP components suggests possible attention processes related to the timing of affective images in addition to changes in pacemaker speed. Early Posterior Negativity (EPN) was larger for positive than for negative images, indicating valence-specific differences in activation of early attention mechanisms. Within the early P1 and the Late Positive Potential (LPP) components, both pleasant and unpleasant stimuli exhibited equal affective modulation. Contingent Negative Variation (CNV) remained independent of both timing performance and affective modulation. This pattern suggests that both pleasant and unpleasant stimuli enhanced arousal and captured attention, but the latter effect was more pronounced for pleasant stimuli. The valence-specificity of affective attention revealed by ERPs combined with behavioral timing results suggests that attention processes indeed contribute to emotion-induced temporal distortions, especially for longer target intervals.     

The insula and evaluative processes

The insula has been implicated as a component of central networks subserving evaluative and affective processes. This study examined evaluative valence and arousal ratings in response to picture stimuli in patients with lesions of the insula and two contrast groups: a control-lesion group (the primary contrast group) and an amygdala-lesion group. Patients rated the positivity and negativity of picture stimuli (from very unpleasant to very pleasant) and how emotionally arousing they found the pictures to be. Compared with patients in the control-lesion group, patients with insular lesions reported reduced arousal in response to both unpleasant and pleasant stimuli, as well as marked attenuation of valence ratings. In contrast, the arousal ratings of patients with amygdala lesions were selectively attenuated for unpleasant stimuli, and these patients' positive and negative valence ratings did not differ from those of the control-lesion group. Results support the view that the insular cortex may play a broad role in integrating affective and cognitive processes, whereas the amygdala may have a more selective role in affective arousal, especially for negative stimuli.     

Eye color and responsiveness to arousing stimuli.

The hypothesis was advanced that dark-eyed subjects are more responsive to arousing stimuli than light-eyed subjects. 40 subjects listened to neutral and arousing auditory stimuli and viewed scenes which were neutral, violent, or sexual in nature. The dependent measure of arousal was a score derived from a combination of physiological responses recorded on a polygraph. Scores were significantly higher for dark-eyed than light-eyed subjects. Significant sex differences were also found, females having higher scores than males. Implications for future research and application were discussed.     

Endogenous cortisol level interacts with noradrenergic activation in the human amygdala

Animal studies show that high cortisol levels exert their effect on stressful task performance via modulation of the amygdala. Availability of noradrenaline in this brain region appears to be a critical prerequisite for this effect. This relationship between noradrenaline and cortisol is explained by an animal model where the amygdala constitutes a crucial region for this interaction. In humans this model has not been extensively tested so far. In a previously reported study human subjects (aged 20.93+/-2.38) were scanned using fMRI when watching sets of emotional and neutral pictures after taking the beta-adrenergic antagonist propranolol or placebo. Stimulus sets consisted of 92 pictures, divided in four emotional categories that ranged from neutral scenes of domestic objects (CAT1) to extremely negative scenes of mutilation or accidents (CAT4). Confrontation with arousing emotional pictures, accompanied by increased noradrenaline levels, evoked increased amygdala activation under placebo but not under betablocker condition. This new and additional analysis of this data set was carried out to determine the effect of differential endogenous cortisol levels on amygdala activation. Cortisol levels during scanning were determined using salivary samples and subjects were post hoc divided in a High (n=14) and Low cortisol group (n=14). When subjects were watching emotional stimuli, presumably associated with enhanced noradrenaline (NA) levels, amygdala activation was contrasted between the two cortisol groups. We hypothesized that emotional stimuli would elicit more amygdala activation in the High than in the Low cortisol group. Here we demonstrate indeed a significant interaction effect of the endogenous cortisol level with increasing activation in the amygdala under placebo but not under betablocker condition, thereby extending the rodent based model of a synergistic effect of the two stress hormones to the human.     

Perceptual asymmetries reflect developmental changes in the neuropsychological mechanisms of emotion recognition

To study how perceptual asymmetries in the recognition of emotion reflect developmental changes in processing affective information, a fused rhyming dichotic word test with positive, negative, and neutral stimuli was administered to adults and children. Results suggested that the hemisphere in which affective information is initially processed affects the strength of perceptual asymmetry and that children's perceptual processing of emotional information is constrained by limited computational resources. Another experiment ruled out effects of volitional shifting of attention to emotional stimuli. These data further confirm that emotional processing involves integration of neural systems across brain regions, including distributed systems that support arousal and recognition. General developmental factors, such as processing capacity, contribute to the coordination of multiple systems responsible for processing emotional information.     

Situation selection across adulthood: the role of arousal

In this study, we investigated age differences in situation selection to understand the role stimulus arousal plays in motivating age differences in this type of emotion regulation. Participants freely selected from a set of affective videos using information about the valence and arousal of each stimulus. There were age differences both in the valence and arousal of selected stimuli. Older adults selected more neutral and low-arousal stimuli while younger adults selected more negative and high-arousal stimuli. We consider these results in light of recent theoretical models and conclude that studies of age differences in emotion regulation must consider both valence and arousal.     

Insular activity during passive viewing of aversive stimuli reflects individual differences in state negative affect

People differ with regard to how they perceive, experience, and express negative affect. While trait negative affect reflects a stable, sustained personality trait, state negative affect represents a stimulus limited and temporally acute emotion. So far, little is known about the neural systems mediating the relationship between negative affect and acute emotion processing. To address this issue we investigated in a healthy female sample how individual differences in state negative affect are reflected in changes in blood oxygen level-dependent responses during passive viewing of emotional stimuli. To assess autonomic arousal we simultaneously recorded changes in skin conductance level. At the psychophysiological level we found increased skin conductance level in response to aversive relative to neutral pictures. However, there was no association of state negative affect with skin conductance level. At the neural level we found that high state negative affect was associated with increased left insular activity during passive viewing of aversive stimuli. The insula has been implicated in interoceptive processes and in the integration of sensory, visceral, and affective information thus contributing to subjective emotional experience. Greater recruitment of the insula in response to aversive relative to neutral stimuli in subjects with high state negative affect may represent increased processing of salient aversive stimuli.     

Modelling audiovisual integration of affect from videos and music

Two experiments examined how affective values from visual and auditory modalities are integrated. Experiment 1 paired music and videos drawn from three levels of valence while holding arousal constant. Experiment 2 included a parallel combination of three levels of arousal while holding valence constant. In each experiment, participants rated their affective states after unimodal and multimodal presentations. Experiment 1 revealed a congruency effect in which stimulus combinations of the same extreme valence resulted in more extreme state ratings than component stimuli presented in isolation. An interaction between music and video valence reflected the greater influence of negative affect. Video valence was found to have a significantly greater effect on combined ratings than music valence. The pattern of data was explained by a five parameter differential weight averaging model that attributed greater weight to the visual modality and increased weight with decreasing values of valence. Experiment 2 revealed a congruency effect only for high arousal combinations and no interaction effects. This pattern was explained by a three parameter constant weight averaging model with greater weight for the auditory modality and a very low arousal value for the initial state. These results demonstrate key differences in audiovisual integration between valence and arousal.     

Effects of age on detection of emotional information

Age differences were examined in affective processing, in the context of a visual search task. Young and older adults were faster to detect high arousal images compared with low arousal and neutral items. Younger adults were faster to detect positive high arousal targets compared with other categories. In contrast, older adults exhibited an overall detection advantage for emotional images compared with neutral images. Together, these findings suggest that older adults do not display valence-based effects on affective processing at relatively automatic stages.