Inhalation of 7.5% carbon dioxide increases threat processing in humans

Hypercapnia Reduces Perceived Heat Pain in Healthy Subjects

BACKGROUND

Danger signals modulate pain perception. Both amplification and attenuation of perceived pain are observed in healthy subjects exposed to danger signals, such as transient threats of an imminent electrical shock. However, exposure to danger signals in real life typically is not transient but constant over minutes to hours. Here, this was experimentally achieved by administering hypercapnic air (7.5% CO2). The primary objective was to investigate whether perceived heat pain would be differentially modulated during this intervention compared to regular air administration. The secondary objective assessed the potential differences of such a modulation with respect to heat intensity level.

METHODS

Thirty-eight participants (19 women) received two air mixtures (hypercapnic and regular air) for 13 min each, during which 18 (6 × 3) noxious heat stimuli of three different intensities were applied to the calf and rated on two scales (intensity and pleasantness/unpleasantness). Psychological and physiological states were compared between conditions using the body sensations questionnaire, self-assessment manikins, heart rate, and galvanic skin response. Statistical analyses were performed using Bayesian estimation testing.

RESULTS

Between-condition differences were statistically meaningful for all heat intensity levels, always showing reduced pain perception during hypercapnia compared to normocapnia. The magnitude of the observed hypoalgesia did not depend on heat intensity levels.

CONCLUSIONS

The presence of a continuous physiological danger signal results in hypoalgesia. Future studies need to determine whether the present results only hold for hypercapnia in healthy subjects or are generalisable to interactions between pain perception and continuous physiological danger signals in clinical pain populations.

SIGNIFICANCE STATEMENT

It was shown that hypercapnia leads to reduced perception of noxious heat stimuli. If confirmed by neural data in future studies this could help to better understand the interaction of pain perception and continuous physiological danger signals in clinical pain conditions, potentially allowing for improved treatment of affected individuals.

Placebo Effects Are Small on Average in the 7.5% CO2 Inhalational Model of Generalized Anxiety

BACKGROUND

Anxiety disorders are highly prevalent and socio-economically costly. Novel pharmacological treatments for these disorders are needed because many patients do not respond to current agents or experience unwanted side effects. However, a barrier to treatment development is the variable and large placebo response rate seen in trials of novel anxiolytics. Despite this, the mechanisms that drive placebo responses in anxiety disorders have been little investigated, possibly due to low availability of convenient experimental paradigms. We aimed to develop and test a novel protocol for inducing placebo anxiolysis in the 7.5% CO2 inhalational model of generalized anxiety in healthy volunteers.

METHODS

Following a baseline 20-minute CO2 challenge, 32 healthy volunteers were administered a placebo intranasal spray labelled as either the anxiolytic "lorazepam" or "saline." Following this, participants surreptitiously underwent a 20-minute inhalation of normal air. Post-conditioning, a second dose of the placebo was administered, after which participants completed another CO2 challenge.

RESULTS

Participants administered sham "lorazepam" reported significant positive expectations of reduced anxiety (P = .001), but there was no group-level placebo effect on anxiety following CO2 challenge post-conditioning (Ps > .350). Surprisingly, we found many participants exhibited unexpected worsening of anxiety, despite positive expectations.

CONCLUSIONS

Contrary to our hypothesis, our novel paradigm did not induce a placebo response, on average. It is possible that effects of 7.5% CO2 inhalation on prefrontal cortex function or behavior in line with a Bayesian predictive coding framework attenuated the effect of expectations on subsequent placebo response. Future studies are needed to explore these possibilities.

Interoceptive Awareness Among the General Public in Saudi Arabia: A Cross-Sectional Study

Background Interoception refers to the cognitive process of perceiving internal bodily states. This encompasses various physiological indicators, including heart rate fluctuations, stomach distention, internal temperature, hydration levels, sensory input from free nerve terminals in the fascia and muscles, as well as hormonal, stretch, and pain receptors. This study aimed to examine the interoceptive awareness among the general public in Saudi Arabia. Methods A cross-sectional online survey was undertaken in Saudi Arabia to investigate the level of interoceptive awareness within the overall population of the country in October 2023. This research used a previously developed questionnaire named the Multidimensional Assessment of Interoceptive Awareness, version 2 (MAIA-2). In a binary logistic regression analysis, the mean interoceptive awareness score of the participants was utilized as the dummy variable to determine the variables that influence interoceptive awareness. Results A total of 814 participants were involved in this study. Overall, the study participants demonstrated a marginal level of interoceptive awareness with a mean score of 94.3 (standard deviation (SD): 29.3) out of 185 (representing 51.0% of the maximum attainable score). The mean interoceptive score was not consistent across different subscales and ranged between 37.7% and 63.3%. The highest mean interoceptive score was observed for the Trusting subscale (9.5 (SD: 4.5) out of 15) (representing 63.3% of the maximum attainable score for this subscale). The lowest mean interoceptive score was observed for the Not-Distracting subscale (11.3 (SD: 6.9) out of 30) (representing 37.7% of the maximum attainable score for this subscale). Binary logistic regression analysis did not identify any statistically significant difference in the likelihood of having a higher level of interoceptive awareness among the participants based on their demographic characteristics (p>0.05). Conclusion The participants in our research demonstrated a modest degree of interoceptive awareness. The study's results suggest that the participants demonstrated a heightened inclination towards internal experiences rather than being attentive to their bodily sensations. Further investigation is required to examine interoceptive awareness across various cohorts.

Interoceptive awareness in a Norwegian population: psychometric properties of the Multidimensional Assessment of Interoceptive Awareness (MAIA) 2

BACKGROUND

Interoception plays a vital role in human cognition and emotion and is an increasingly important part of clinical studies of mind-body approaches and mental health. Interoceptive awareness (IA) encompasses numerous mind-body components and can be assessed by employing a self-report measure such as the Multidimensional Assessment of Interoceptive Awareness (MAIA), which has been adapted and validated across several countries and is used in experimental and clinical settings. In this study, the MAIA-2, which was developed due to the psychometric shortages of MAIA, was thoroughly translated, and its psychometric features were examined in a sample of 306 Norwegian-speaking participants (81% females, ages 16 through 66 plus).

METHODS

The participants completed the MAIA-2 Norwegian version (MAIA-2-N) and the COOP/WONCA Functional Assessment Charts measuring psychological, physical, and overall health. The following psychometric qualities of the MAIA-2 were investigated: factor structure, internal consistency, and the moderating role of gender.

RESULTS

Confirmatory Factor Analysis (CFA) revealed that an 8-factor model of MAIA-2-N provided the best fit. Also, a bifactor model revealed a proper fit. Good internal consistency and a moderating role of gender, age, and education on the relationships between certain MAIA-2-N factors and health were observed.

CONCLUSIONS

The MAIA-2-N is an adequate measure of IA in Norwegian-speaking individuals. The factor-structure corresponds with the original MAIA-2 and it shows good internal consistency. Some moderating effects of gender were observed, particularly related to the relationship between IA and physical and psychological state, with the physical state/fitness more closely linked to IA in males and psychological state in females.

The impact of anxiety on postural control: CO2 challenge model

Anxiety and balance and postural control are linked via common neural pathways, such as the parabrachial nucleus network. A laboratory-based model of general anxiety disorder (GAD) using the CO₂ challenge, has potential to be used to observe this relationship, potentially mimicking subjective, autonomic, and neuropsychological features of GAD. The current feasibility study used the CO₂ challenge to explore postural control changes in healthy adults. It was predicted that during the CO₂ condition, participants would show increased postural sway path length and decreased sway stability, compared with a normal air breathing condition. To assess this, heart and breathing rate, quiet standing postural sway path length, sway dynamic stability, and subjective measures of emotion were measured either before and after or during and after the inhalation conditions. Results demonstrated that CO₂ inhalation led to both an increase in sway path length and reduced sway stability compared to the air breathing conditions; the effect on sway path lasted after the inhalation of CO₂ had ceased. Additionally, replication of HR and subjective measures of emotion were observed when comparing air and CO₂ conditions. This provides experimental evidence that CO₂ inhalation can affect balance, suggestive of shared mechanisms between anxiety and balance performance, as well as indicating that the CO₂ model of GAD is suitable to look at changes in balance performance in healthy adults. Future use of this model to explore factors that can reduce the influence of GAD on balance would be beneficial as would a more detailed exploration of the neural pathways associated with the associated comorbidity.

Experimentally induced and real-world anxiety have no demonstrable effect on goal-directed behaviour

BACKGROUND

Goal-directed control guides optimal decision-making and it is an important cognitive faculty that protects against developing habits. Previous studies have found some evidence of goal-directed deficits when healthy individuals are stressed, and in psychiatric conditions characterised by compulsive behaviours and anxiety. Here, we tested if goal-directed control is affected by state anxiety, which might explain the former results.

METHODS

We carried out a causal test of this hypothesis in two experiments (between-subject N = 88; within-subject N = 50) that used the inhalation of hypercapnic gas (7.5% CO2) to induce an acute state of anxiety in healthy volunteers. In a third experiment (N = 1413), we used a correlational design to test if real-life anxiety-provoking events (panic attacks, stressful events) are associated with impaired goal-directed control.

RESULTS

In the former two causal experiments, we induced a profoundly anxious state, both physiologically and psychologically, but this did not affect goal-directed performance. In the third, correlational, study, we found no evidence for an association between goal-directed control, panic attacks or stressful life eventsover and above variance accounted for by trait differences in compulsivity.

CONCLUSIONS

In sum, three complementary experiments found no evidence that anxiety impairs goal-directed control in human subjects.

Baseline Differences in Anxiety Affect Attention and tDCS-Mediated Learning

Variable responses to transcranial direct current stimulation (tDCS) protocols across individuals are widely reported, but the reasons behind this variation are unclear. This includes tDCS protocols meant to improve attention. Attentional control is impacted by top-down and bottom-up processes, and this relationship is affected by state characteristics such as anxiety. According to Attentional Control Theory, anxiety biases attention towards bottom-up and stimulus-driven processing. The goal of this study was to explore the extent to which differences in state anxiety and related measures affect visual attention and category learning, both with and without the influence of tDCS. Using discovery learning, participants were trained to classify pictures of European streets into two categories while receiving 30 min of 2.0 mA anodal, cathodal, or sham tDCS over the rVLPFC. The pictures were classifiable according to two separate rules, one stimulus and one hypothesis-driven. The Remote Associates Test (RAT), Profile of Mood States, and Attention Networks Task (ANT) were used to understand the effects of individual differences at baseline on subsequent tDCS-mediated learning. Multinomial logistic regression was fit to predict rule learning based on the baseline measures, with subjects classified according to whether they used the stimulus-driven or hypothesis-driven rule to classify the pictures. The overall model showed a classification accuracy of 74.1%. The type of tDCS stimulation applied, attentional orienting score, and self-reported mood were significant predictors of different categories of rule learning. These results indicate that anxiety can influence the quality of subjects' attention at the onset of the task and that these attentional differences can influence tDCS-mediated category learning during the rapid assessment of visual scenes. These findings have implications for understanding the complex interactions that give rise to the variability in response to tDCS.

Effects of 7.5% Carbon Dioxide and Nicotine Administration on Latent Inhibition

Stratified medicine approaches have potential to improve the efficacy of drug development for schizophrenia and other psychiatric conditions, as they have for oncology. Latent inhibition is a candidate biomarker as it demonstrates differential sensitivity to key symptoms and neurobiological abnormalities associated with schizophrenia. The aims of this research were to evaluate whether a novel latent inhibition task that is not confounded by alternative learning effects such as learned irrelevance, is sensitive to (1) an in-direct model relevant to psychosis [using 7.5% carbon dioxide (CO₂) inhalations to induce dopamine release via somatic anxiety] and (2) a pro-cognitive pharmacological manipulation (via nicotine administration) for the treatment of cognitive impairment associated with schizophrenia. Experiment 1 used a 7.5% CO₂ challenge as a model of anxiety-induced dopamine release to evaluate the sensitivity of latent inhibition during CO₂ gas inhalation, compared to the inhalation of medical air. Experiment 2 examined the effect of 2 mg nicotine administration vs. placebo on latent inhibition to evaluate its sensitivity to a potential pro-cognitive drug treatment. Inhalation of 7.5% CO₂ raised self-report and physiological measures of anxiety and impaired latent inhibition, relative to a medical air control; whereas administration of 2 mg nicotine, demonstrated increased latent inhibition relative to placebo control. Here, two complementary experimental studies suggest latent inhibition is modified by manipulations that are relevant to the detection and treatment of schizophrenia. These results suggest that this latent inhibition task merits further investigation in the context of neurobiological sub-groups suitable for novel treatment strategies.

Effects of state anxiety on gait: a 7.5% carbon dioxide challenge study

We used the 7.5% carbon dioxide (CO₂) model of anxiety induction to investigate the effects of state anxiety on normal gait and gait when navigating an obstacle. Healthy volunteers (n = 22) completed a walking task during inhalations of 7.5% CO₂ and medical air (placebo) in a within-subjects design. The order of inhalation was counterbalanced across participants and the gas was administered double-blind. Over a series of trials, participants walked the length of the laboratory, with each trial requiring participants to navigate through an aperture (width adjusted to participant size), with gait parameters measured via a motion capture system. The main findings were that walking speed was slower, but the adjustment in body orientation was greater, during 7.5% CO₂ inhalation compared to air. These findings indicate changes in locomotor behaviour during heightened state anxiety that may reflect greater caution when moving in an agitated state. Advances in sensing technology offer the opportunity to monitor locomotor behaviour, and these findings suggest that in doing so, we may be able to infer emotional states from movement in naturalistic settings.

Understanding rat emotional responses to CO2

The aim of this review is to summarize evidence regarding rat emotional experiences during carbon dioxide (CO₂) exposure. The studies reviewed show that CO₂ exposure is aversive to rats, and that rats respond to CO₂ exposure with active and passive defense behaviors. Plasma corticosterone and bradycardia increased in rats exposed to CO₂. As with anxiogenic drugs, responses to CO₂ are counteracted by the administration of anxiolytics, SRIs, and SSRI's. Human studies reviewed indicate that, when inhaling CO₂, humans experience feelings of anxiety fear and panic, and that administration of benzodiazepines, serotonin precursors, and SSRIs ameliorate these feelings. In vivo and in vitro rat studies reviewed show that brain regions, ion channels, and neurotransmitters involved in negative emotional responses are activated by hypercapnia and acidosis associated with CO₂ exposure. On the basis of the behavioral, physiological, and neurobiological evidence reviewed, we conclude that CO₂ elicits negative emotions in rats.

Fossil Fuel Combustion Is Driving Indoor CO2 Toward Levels Harmful to Human Cognition

Human activities are elevating atmospheric carbon dioxide concentrations to levels unprecedented in human history. The majority of anticipated impacts of anthropogenic CO2 emissions are mediated by climate warming. Recent experimental studies in the fields of indoor air quality and cognitive psychology and neuroscience, however, have revealed significant direct effects of indoor CO2 levels on cognitive function. Here, we shed light on this connection and estimate the impact of continued fossil fuel emissions on human cognition. We conclude that indoor CO2 levels may indeed reach levels harmful to cognition by the end of this century, and the best way to prevent this hidden consequence of climate change is to reduce fossil fuel emissions. Finally, we offer recommendations for a broad, interdisciplinary approach to improving such understanding and prediction.

Brain Functional Connectivity Correlates of Response in the 7.5% CO2 Inhalational Model of Generalized Anxiety Disorder: A Pilot Study

BACKGROUND

The 7.5% CO2 inhalational model can be used to explore potential treatments for generalized anxiety disorder. However, it is unknown how inter-individual variability in the functional architecture of negative affective valence systems might relate to anxiogenic response in this model.

METHODS

A total of 13 healthy volunteers underwent functional magnetic resonance imaging during a passive emotional face perception task. We explored task-evoked functional connectivity in the potential threat system through generalized psychophysiological interaction analysis. Within 7 days, these participants underwent prolonged 7.5% CO2 inhalation, and results from the generalized psychophysiological interaction analysis were correlated with CO2 outcome measures.

RESULTS

Functional connectivity between ventromedial prefrontal cortex and right amygdala positively correlated with heart rate and subjective anxiety, while connectivity between midcingulate cortex and left amygdala negatively correlated with anxiety during CO2 challenge.

CONCLUSIONS

Response to CO2 challenge correlated with task-evoked functional connectivity in the potential threat system. Further studies should assess whether this translates into clinical populations.

Acute anxiety and autonomic arousal induced by CO2 inhalation impairs prefrontal executive functions in healthy humans

Acute anxiety impacts cognitive performance. Inhalation of air enriched with carbon dioxide (CO2) in healthy humans provides a novel experimental model of generalised anxiety, but has not previously been used to assess cognition. We used inhalation of 7.5% CO2 to induce acute anxiety and autonomic arousal in healthy volunteers during neuropsychological tasks of cognitive flexibility, emotional processing and spatial working memory in a single-blind, placebo-controlled, randomized, crossover, within-subjects study. In Experiment 1 (n = 44), participants made significantly more extra-dimensional shift errors on the Cambridge Neuropsychological Test Automated Battery (CANTAB) Intra-Extra Dimensional Set Shift task under CO2 inhalation compared with 'normal' air. Participants also had slower latencies when responding to positive words and made significantly more omission errors for negative words on the CANTAB Affective Go/No-go task. In Experiment 2 (n = 28), participants made significantly more total errors and had poorer heuristic search strategy on the CANTAB Spatial Working Memory task. In both experiments, CO2 inhalation significantly increased negative affect; state anxiety and fear; symptoms of panic; and systolic blood pressure/heart rate. Overall, CO2 inhalation produced robust anxiogenic effects and impaired fronto-executive functions of cognitive flexibility and working memory. Effects on emotional processing suggested a mood-congruent slowing in processing speed in the absence of a negative attentional bias. State-dependent effects of anxiety on cognitive-emotional interactions in the prefrontal cortex warrant further investigation.

Modeling anxiety in healthy humans: a key intermediate bridge between basic and clinical sciences

Animal models of anxiety disorders are important for elucidating neurobiological defense mechanisms. However, animal models are limited when it comes to understanding the more complex processes of anxiety that are unique to humans (e.g., worry) and to screen new treatments. In this review, we outline how the Experimental Psychopathology approach, based on experimental models of anxiety in healthy subjects, can mitigate these limitations and complement research in animals. Experimental psychopathology can bridge basic research in animals and clinical studies, as well as guide and constrain hypotheses about the nature of psychopathology, treatment mechanisms, and treatment targets. This review begins with a brief review of the strengths and limitations of animal models before discussing the need for human models of anxiety, which are especially necessary to probe higher-order cognitive processes. This can be accomplished by combining anxiety-induction procedures with tasks that probe clinically relevant processes to identify neurocircuits that are potentially altered by anxiety. The review then discusses the validity of experimental psychopathology and introduces a methodological approach consisting of five steps: (1) select anxiety-relevant cognitive or behavioral operations and associated tasks, (2) identify the underlying neurocircuits supporting these operations in healthy controls, 3) examine the impact of experimental anxiety on the targeted operations in healthy controls, (4) utilize findings from step 3 to generate hypotheses about neurocircuit dysfunction in anxious patients, and 5) evaluate treatment mechanisms and screen novel treatments. This is followed by two concrete illustrations of this approach and suggestions for future studies.

State anxiety and information processing: A 7.5% carbon dioxide challenge study

We used the 7.5% carbon dioxide model of anxiety induction to investigate the effects of state anxiety on simple information processing. In both high- and low-anxious states, participants (n = 36) completed an auditory–visual matching task and a visual binary categorization task. The stimuli were either degraded or clear, so as to investigate whether the effects of anxiety are greater when signal clarity is compromised. Accuracy in the matching task was lower during CO₂ inhalation and for degraded stimuli. In the categorization task, response times and indecision (measured using mouse trajectories) were greater during CO₂ inhalation and for degraded stimuli. For most measures, we found no evidence of Gas × Clarity interactions. These data indicate that state anxiety negatively impacts simple information processing and do not support claims that anxiety may benefit performance in low-cognitively-demanding tasks. These findings have important implications for understanding the impact of state anxiety in real-world situations.

State anxiety and emotional face recognition in healthy volunteers

High trait anxiety has been associated with detriments in emotional face processing. By contrast, relatively little is known about the effects of state anxiety on emotional face processing. We investigated the effects of state anxiety on recognition of emotional expressions (anger, sadness, surprise, disgust, fear and happiness) experimentally, using the 7.5% carbon dioxide (CO2) model to induce state anxiety, and in a large observational study. The experimental studies indicated reduced global (rather than emotion-specific) emotion recognition accuracy and increased interpretation bias (a tendency to perceive anger over happiness) when state anxiety was heightened. The observational study confirmed that higher state anxiety is associated with poorer emotion recognition, and indicated that negative effects of trait anxiety are negated when controlling for state anxiety, suggesting a mediating effect of state anxiety. These findings may have implications for anxiety disorders, which are characterized by increased frequency, intensity or duration of state anxious episodes.

Pharmacotherapy in Generalized Anxiety Disorder: Novel Experimental Medicine Models and Emerging Drug Targets

Many pharmacological and psychological approaches have been found efficacious in patients with generalized anxiety disorder (GAD), but many treatment-seeking patients will not respond and others will relapse despite continuing with interventions that initially had beneficial effects. Other patients will respond but then stop treatment early because of untoward effects such as sexual dysfunction, drowsiness, and weight gain. There is much scope for the development of novel approaches that could have greater overall effectiveness or acceptability than currently available interventions or that have particular effectiveness in specific clinical subgroups. 'Experimental medicine' studies in healthy volunteers model disease states and represent a proof-of-concept approach for the development of novel therapeutic interventions: they determine whether to proceed to pivotal efficacy studies and so can reduce delays in translating innovations into clinical practice. Investigations in healthy volunteers challenged with the inhalation of air 'enriched' with 7.5% carbon dioxide (CO₂) indicate this technique provides a validated and robust experimental medicine model, mirroring the subjective, autonomic, and cognitive features of GAD. The anxiety response during CO₂ challenge probably involves both central noradrenergic neurotransmission and effects on acid-base sensitive receptors and so may stimulate development of novel agents targeted at central chemosensors. Increasing awareness of the potential role of altered cytokine balance in anxiety and the interplay of cytokines with monoaminergic mechanisms may also encourage the investigation of novel agents with modulating effects on immunological profiles. Although seemingly disparate, these two approaches to treatment development may pivot on a shared mechanism in exerting anxiolytic-like effects through pharmacological effects on acid-sensing ion channels.

Biological markers for anxiety disorders, OCD and PTSD: A consensus statement. Part II: Neurochemistry, neurophysiology and neurocognition

OBJECTIVE

Biomarkers are defined as anatomical, biochemical or physiological traits that are specific to certain disorders or syndromes. The objective of this paper is to summarise the current knowledge of biomarkers for anxiety disorders, obsessive-compulsive disorder (OCD) and posttraumatic stress disorder (PTSD).

METHODS

Findings in biomarker research were reviewed by a task force of international experts in the field, consisting of members of the World Federation of Societies for Biological Psychiatry Task Force on Biological Markers and of the European College of Neuropsychopharmacology Anxiety Disorders Research Network.

RESULTS

The present article (Part II) summarises findings on potential biomarkers in neurochemistry (neurotransmitters such as serotonin, norepinephrine, dopamine or GABA, neuropeptides such as cholecystokinin, neurokinins, atrial natriuretic peptide, or oxytocin, the HPA axis, neurotrophic factors such as NGF and BDNF, immunology and CO2 hypersensitivity), neurophysiology (EEG, heart rate variability) and neurocognition. The accompanying paper (Part I) focuses on neuroimaging and genetics.

CONCLUSIONS

Although at present, none of the putative biomarkers is sufficient and specific as a diagnostic tool, an abundance of high quality research has accumulated that should improve our understanding of the neurobiological causes of anxiety disorders, OCD and PTSD.

Acute anxiety and social inference: An experimental manipulation with 7.5% carbon dioxide inhalation

BACKGROUND

Positive self-bias is thought to be protective for mental health. We previously found that the degree of positive bias when learning self-referential social evaluation decreases with increasing social anxiety. It is unclear whether this reduction is driven by differences in state or trait anxiety, as both are elevated in social anxiety; therefore, we examined the effects on the state of anxiety induced by the 7.5% carbon dioxide (CO2) inhalation model of generalised anxiety disorder (GAD) on social evaluation learning.

METHODS

For our study, 48 (24 of female gender) healthy volunteers took two inhalations (medical air and 7.5% CO2, counterbalanced) whilst learning social rules (self-like, self-dislike, other-like and other-dislike) in an instrumental social evaluation learning task. We analysed the outcomes (number of positive responses and errors to criterion) using the random effects Poisson regression.

RESULTS

Participants made fewer and more positive responses when breathing 7.5% CO2 in the other-like and other-dislike rules, respectively (gas × condition × rule interaction p = 0.03). Individuals made fewer errors learning self-like than self-dislike, and this positive self-bias was unaffected by CO2. Breathing 7.5% CO2 increased errors, but only in the other-referential rules (gas × condition × rule interaction p = 0.003).

CONCLUSIONS

Positive self-bias (i.e. fewer errors learning self-like than self-dislike) seemed robust to changes in state anxiety. In contrast, learning other-referential evaluation was impaired as state anxiety increased. This suggested that the previously observed variations in self-bias arise due to trait, rather than state, characteristics.

A Good Death? Report of the Second Newcastle Meeting on Laboratory Animal Euthanasia

Simple Summary

Millions of laboratory animals are killed each year worldwide. However, there is a lack of consensus regarding what methods of killing are humane for many species and stages of development. This report summarises research findings and discussions from an international meeting of experts and stakeholders, with recommendations to inform good practice for humane killing of mice, rats and zebrafish. It provides additional guidance and perspectives for researchers designing projects that involve euthanasing animals, researchers studying aspects of humane killing, euthanasia device manufacturers, regulators, and institutional ethics or animal care and use committees that wish to review local practice.

Abstract

Millions of laboratory animals are killed each year worldwide. There is an ethical, and in many countries also a legal, imperative to ensure those deaths cause minimal suffering. However, there is a lack of consensus regarding what methods of killing are humane for many species and stages of development. In 2013, an international group of researchers and stakeholders met at Newcastle University, United Kingdom to discuss the latest research and which methods could currently be considered most humane for the most commonly used laboratory species (mice, rats and zebrafish). They also discussed factors to consider when making decisions about appropriate techniques for particular species and projects, and priorities for further research. This report summarises the research findings and discussions, with recommendations to help inform good practice for humane killing.

Dynamic Dazzle Distorts Speed Perception

Static high contrast (‘dazzle’) patterns, such as zigzags, have been shown to reduce the perceived speed of an object. It has not escaped our notice that this effect has possible military applications and here we report a series of experiments on humans, designed to establish whether dynamic dazzle patterns can cause distortions of perceived speed sufficient to provide effective defence in the field, and the extent to which these effects are robust to a battery of manipulations. Dynamic stripe patterns moving in the same direction as the target are found to increase the perceived speed of that target, whilst dynamic stripes moving in the opposite direction to the target reduce the perceived speed. We establish the optimum position for such dazzle patches; confirm that reduced contrast and the addition of colour do not affect the performance of the dynamic dazzle, and finally, using the CO₂ challenge, show that the effect is robust to stressful conditions.

Anxiety sensitivity and trait anxiety are associated with response to 7.5% carbon dioxide challenge

The 7.5% carbon dioxide (CO2) inhalation model is used to provoke acute anxiety, for example to investigate the effects of anxiety on cognitive processes, or the efficacy of novel anxiolytic agents. However, little is known about the relationship of baseline anxiety sensitivity or trait anxiety (i.e., anxiety proneness), with an individual's response to the 7.5% CO2 challenge. We examined data from a number of 7.5% CO2 challenge studies to determine whether anxiety proneness was related to subjective or physiological response. Our findings indicate anxiety proneness is associated with greater subjective and physiological responses. However, anxiety-prone individuals also have a greater subjective response to the placebo (medical air) condition. This suggests that anxiety-prone individuals not only respond more strongly to the 7.5% CO2 challenge, but also to medical air. Implications for the design and conduct of 7.5% CO2 challenge studies are discussed.

Measuring inhibitory processes for alcohol-related attentional biases: introducing a novel attentional bias measure

INTRODUCTION

Attentional biases for alcohol related information (AB) have often been reported for heavy drinkers. These attentional biases have been found to have predictive value regarding relapse in abstaining alcoholics. Similarly impaired inhibitory processes have also been found to be associated with heavy drinkers. This paper describes a new experimental paradigm that can be utilised to investigate attentional bias towards alcohol-related visual stimuli, specifically the ability to inhibit the orientation of initial and sustained attention, towards peripherally appearing stimuli. In this way we hope to study a novel aspect of attentional biases and how they relate to substance abuse.

METHODS

We used a novel eye-tracking task which aims to measure inhibitory processes for AB. The experiment utilised a gaze contingency paradigm to measure the compulsion to process or attend to alcohol stimuli. 86 undergraduate participants were recruited (31 males; 55 females), aged 18-49 years (m = 20.88; sd = 4.52). A 'break frequency' variable was computed for each participant. This was the number of times that participants tried to look at peripheral stimuli. We argue that this variable is a direct measure of how distracting peripheral stimuli were.

RESULTS

It was found that reported alcohol use was associated with the eye-tracking break frequency measure of inhibitory control. Thus, heavy drinking may be associated with decreased inhibitory control and increased attentional bias.

CONCLUSIONS

Results suggest that attentional bias is not just a process of stimuli becoming prioritised, but also stimuli becoming compulsory to attend and process.

Early effects of duloxetine on emotion recognition in healthy volunteers

The serotonin-noradrenaline reuptake inhibitor (SNRI) duloxetine is an effective treatment for major depression and generalised anxiety disorder. Neuropsychological models of antidepressant drug action suggest therapeutic effects might be mediated by the early correction of maladaptive biases in emotion processing, including the recognition of emotional expressions. Sub-chronic administration of duloxetine (for two weeks) produces adaptive changes in neural circuitry implicated in emotion processing; however, its effects on emotional expression recognition are unknown. Forty healthy participants were randomised to receive either 14 days of duloxetine (60 mg/day, titrated from 30 mg after three days) or matched placebo (with sham titration) in a double-blind, between-groups, repeated-measures design. On day 0 and day 14 participants completed a computerised emotional expression recognition task that measured sensitivity to the six primary emotions. Thirty-eight participants (19 per group) completed their course of tablets and were included in the analysis. Results provide evidence that duloxetine, compared to placebo, may reduce the accurate recognition of sadness. Drug effects were driven by changes in participants' ability to correctly detect subtle expressions of sadness, with greater change observed in the placebo relative to the duloxetine group. These effects occurred in the absence of changes in mood. Our preliminary findings require replication, but complement recent evidence that sadness recognition is a therapeutic target in major depression, and a mechanism through which SNRIs could resolve negative biases in emotion processing to achieve therapeutic effects.

Effects of 7.5% carbon dioxide (CO2) inhalation and ethnicity on face memory

The ability to accurately verify facial identity has important forensic implications, but this ability is fallible. Research suggests that anxiety at the time of encoding can impair subsequent recall, but no studies have investigated the effects of anxiety at the time of recall in an experimental paradigm. This study addresses this gap using the carbon dioxide (CO₂) model of anxiety induction. Thirty participants completed two inhalations: one of 7.5% CO₂-enriched air and one of medical air (i.e., placebo). Prior to each inhalation, participants were presented with 16 facial images (50% own-ethnicity, 50% other-ethnicity). During the inhalation they were required to identify which faces had been seen before from a set of 32 images (16 seen-before and 16 novel images). Identification accuracy was lower during CO₂ inhalation compared to air (F[1,29] = 5.5, p = .026, η_p² = .16), and false alarm rate was higher for other-ethnicity faces compared to own-ethnicity faces (F[1,29] = 11.3, p = .002, η_p² = .28). There was no evidence of gas by ethnicity interactions for accuracy or false alarms (ps > .34). Ratings of decision confidence did not differ by gas condition, suggesting that participants were unaware of differences in performance. These findings suggest that anxiety, at the point of recognition, impairs facial identification accuracy. This has substantial implications for eyewitness memory situations, and suggests that efforts should be made to attenuate the anxiety in these situations in order to improve the validity of identification.

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Use of carbon dioxide challenge to investigate acute anxiety effects on face memory

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Investigation of the “own-ethnicity” effect and its interaction with acute anxiety

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Results show decreased accuracy for face memory during acutely anxious states.

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Results show increased false identifications when viewing other ethnicity faces.

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Efforts should be made to attenuate anxiety in eye witness situations.

Evaluating psychological interventions in a novel experimental human model of anxiety

Inhalation of 7.5% carbon dioxide increases anxiety and autonomic arousal and provides a novel experimental model of anxiety with which to evaluate pharmacological and psychological treatments for anxiety. To date several psychotropic drugs including benzodiazepines, SSRIs and SNRIs have been evaluated using the 7.5% CO2 model; however, it has yet to be used to evaluate psychological interventions. We compared the effects of two core psychological components of mindfulness-meditation (open monitoring and focused attention) against general relaxation, on subjective, autonomic and neuropsychological outcomes in the 7.5% CO2 experimental model. 32 healthy screened adults were randomized to complete 10 min of guided open monitoring, focused attention or relaxation, immediately before inhaling 7.5% CO2 for 20 min. During CO2-challenge participants completed an eye-tracking measure of attention control and selective attention. Measures of subjective anxiety, blood pressure and heart rate were taken at baseline and immediately following intervention and CO2-challenge. OM and FA practice reduced subjective feelings of anxiety during 20-min inhalation of 7.5% CO2 compared to relaxation control. OM practice produced a strong anxiolytic effect, whereas the effect of FA was more modest. Anxiolytic OM and FA effects occurred in the absence of group differences in autonomic arousal and eye-movement measures of attention. Our findings are consistent with neuropsychological models of mindfulness-meditation that propose OM and FA activate prefrontal mechanisms that support emotion regulation during periods of anxiety and physiological hyper-arousal. Our findings complement those from pharmacological treatment studies, further supporting the use of CO2 challenge to evaluate future therapeutic interventions for anxiety.

Interactions of CO2with various functional molecules

We report the CO₂-interactions with diverse functional molecules. Useful functional molecules such as melamine showing very large adsorption enthalpy for CO₂are reported.

Defensive eye-blink startle responses in a human experimental model of anxiety

Inhalation of low concentrations of carbon dioxide (CO2) triggers anxious behaviours in rodents via chemosensors in the amygdala, and increases anxiety, autonomic arousal and hypervigilance in healthy humans. However, it is not known whether CO2 inhalation modulates defensive behaviours coordinated by this network in humans. We examined the effect of 7.5% CO2 challenge on the defensive eye-blink startle response. A total of 27 healthy volunteers completed an affective startle task during inhalation of 7.5% CO2 and air. The magnitude and latency of startle eye-blinks were recorded whilst participants viewed aversive and neutral pictures. We found that 7.5% CO2 increased state anxiety and raised concurrent measures of skin conductance and heart rate (HR). CO2 challenge did not increase startle magnitude, but slowed the onset of startle eye-blinks. The effect of CO2 challenge on HR covaried with its effects on both subjective anxiety and startle latency. Our findings are discussed with reference to startle profiles during conditions of interoceptive threat, increased cognitive load and in populations characterised by anxiety, compared with acute fear and panic.

Effects of 7.5% carbon dioxide inhalation on anxiety and mood in cigarette smokers

Cigarette smoking is associated with elevated risk of anxiety and mood disorder. Using the 7.5% carbon dioxide (CO2) inhalation model of anxiety induction, we examined the effects of smoking status and abstinence from smoking on anxiety responses. Physiological and subjective responses to CO2 and medical air were compared in smokers and non-smokers (Experiment One) and in overnight abstinent and non-abstinent smokers (Experiment Two). CO2 induced greater increases in blood pressure in non-smokers compared with smokers (ps < 0.043), and greater increases in anxiety (p = 0.005) and negative affect (p = 0.054) in non-abstinent compared with abstinent smokers. CO2 increased physiological and subjective indices of anxiety. There were differences across smoking groups indicating that the CO2 inhalation model is a useful tool for examining the relationship between smoking and anxiety. The findings suggested that both acute smoking and acute abstinence may protect against anxious responding. Further investigation is needed in long-term heavy smokers.

The effect of focused attention and open monitoring meditation on attention network function in healthy volunteers

Mindfulness meditation techniques are increasingly popular both as a life-style choice and therapeutic adjunct for a range of mental and physical health conditions. However, little is known about the mechanisms through which mindfulness meditation and its constituent practices might produce positive change in cognition and emotion. Our study directly compared the effects of Focused Attention (FA) and Open-Monitoring (OM) meditation on alerting, orienting and executive attention network function in healthy individuals. Participants were randomized to three intervention groups: open-focused meditation, focused attention, and relaxation control. Participants completed an emotional variant of the Attention Network Test (ANT) at baseline and post-intervention. OM and FA practice improved executive attention, with no change observed in the relaxation control group. Improvements in executive attention occurred in the absence of change in subjective/self-report mood and cognitive function. Baseline levels of dispositional/trait mindfulness were positively correlated with executive control in the ANT at baseline. Our results suggest that mindfulness meditation might usefully target deficits in executive attention that characterise mood and anxiety disorders.

Acute Anxiety Impairs Accuracy in Identifying Photographed Faces

We investigated whether acutely induced anxiety modifies the ability to match photographed faces. Establishing the extent to which anxiety affects face-matching accuracy is important because of the relevance of face-matching performance to critical security-related applications. Participants ( N = 28) completed the Glasgow Face Matching Test twice, once during a 20-min inhalation of medical air and once during a similar inhalation of air enriched with 7.5% CO2, which is a validated method for inducing acute anxiety. Anxiety degraded performance, but only with respect to hits, not false alarms. This finding provides further support for the dissociation between the ability to accurately identify a genuine match between faces and the ability to identify the lack of a match. Problems with the accuracy of facial identification are not resolved even when viewers are presented with a good photographic image of a face, and identification inaccuracy may be heightened when viewers are experiencing acute anxiety.

Attention control in mood and anxiety disorders: evidence from the antisaccade task

The antisaccade task (in which participants must suppress a reflexive saccade towards a sudden, peripheral stimulus and generate a volitional saccade in the opposite direction) is considered a measure of cognitive inhibition. The task has been used to examine cognitive control deficits in several neuropsychiatric conditions, most notably schizophrenia. This commentary summarizes recent evidence from antisaccade tasks in mood and anxiety disorders, with reference to neuropsychological models and psychopharmacological mechanisms.

Inhalation of 7.5% carbon dioxide increases alerting and orienting attention network function

RATIONALE

The development of experimental models that readily translate between animals and humans is required to better integrate and clarify the biological, behavioural and cognitive mechanisms that underlie normal fear and pathological anxiety. Inhalation of low concentrations of carbon dioxide (CO(2)) increases anxiety and autonomic arousal in humans, triggers related behaviours in small animals, and increases selective attention to threat in healthy humans. However the effects on broader cognitive (non-emotional) processes that characterize anxiety are not known.

OBJECTIVES

To examine the effect of 7.5 % CO(2) inhalation (vs. air) on the efficiency of discrete attention networks implicated in anxiety: alerting (maintaining an alert state), orienting (the selection of information from sensory input) and executive control (resolving cognitive conflict).

METHODS

Twenty-three healthy human participants completed a computerized Attention Network Test (ANT) during inhalation of 7.5 % CO(2) enriched and normal/medical air. Gas was administered blind to participants with inhalation order counterbalanced across participants. Measures of heart rate, blood pressure and subjective mood/anxiety were obtained at baseline and following each inhalation period.

RESULTS

CO(2) inhalation increased anxiety, autonomic arousal and the efficiency of alerting and orienting attention network function. Autonomic response to CO(2) correlated with increased orienting; and CO(2)-induced anxiety, autonomic arousal and orienting network function increased with chronic (trait) anxiety.

CONCLUSIONS

Evidence that CO(2) modulates attention mechanisms involved in the temporal detection and spatial location of salient stimuli converges with evidence that CO(2) triggers fear behaviour in animals via direct innervation of a distributed neural network that facilitates environmental hypervigilance.

Acutely induced anxiety increases negative interpretations of events in a closed-circuit television monitoring task

In two experiments we measured the effects of 7.5% CO₂ inhalation on the interpretation of video footage recorded on closed circuit television (CCTV). As predicted, inhalation of 7.5% CO₂ was associated with increases in physiological and subjective correlates of anxiety compared with inhalation of medical air (placebo). Importantly, when in the 7.5% CO₂ condition, participants reported the increased presence of suspicious activity compared with placebo (Experiment 1), a finding that was replicated and extended (Experiment 2) with no concomitant increase in the reporting of the presence of positive activity. These findings support previous work on interpretative bias in anxiety but are novel in terms of how the anxiety was elicited, the nature of the interpretative bias, and the ecological validity of the task.

Attentional control moderates fearful responding to a 35% CO(2) challenge

Attentional control (AC) is an individual difference variable indexing the ability to voluntarily focus attention and shift attention when desired. AC is thought to impact the experience of fear by facilitating the disengagement of attention from threat and promoting the deployment of attentional resources toward regulatory or coping strategies. Whereas previous research has focused on visual threat cues, in the current study we examined whether this model also applies to interoceptive threat by evaluating the extent to which individual differences in AC moderated the relationship between trait anxiety and self-reported fear in response to a single vital capacity inhalation of a 35% CO(2), 65% balanced O(2) gas mixture. The sample comprised a large nonclinical group of young adults (N=128). Results indicated that AC moderated the relationship between trait anxiety and fearful responding to the challenge. Findings suggest that AC plays a significant and clinically important role in modulating self-reported fear.

The effects of 7.5% carbon dioxide inhalation on task performance in healthy volunteers

Studies have shown that anxiety can positively or negatively affect performance with respect to focusing of attention or distractibility, subjective workload and effort (Humphreys and Revelle, 1984). The inhalation of carbon dioxide (CO(2)) is associated with physiological and psychological effects of anxiety (Bailey et al., 2005) but its effects on performance have rarely been reported. The studies reported here looked at the effects of CO(2) inhalation on physiological and subjective measures and performance on two tasks. Eight healthy male participants completed a tracking task with a reaction time component, and 12 healthy participants (six male) completed a complex target identification task. Tasks were performed during 20-min inhalations of 7.5% CO(2)/21% O(2)/71.5% N(2) mixture or medical air. Continuous heart rate and blood pressure measures were taken, in addition to subjective measures of mood and workload. In comparison with air, CO(2) increased heart rate and blood pressure, increased subjective scores of panic, anxiety, fear, and tension, and reduced subjective scores of relaxation and happiness. Attention was focussed when inhaling CO(2) during the simple task, and central demand was greater when inhaling CO(2) during the complex task. Therefore, inhalation of 7.5% CO(2) produces effects on task performance which are consistent with anxiety.

Emotional processing and antidepressant action

Negative affective schema and associated biases in information processing have long been associated with clinical depression. Such an approach has guided the development of successful psychological therapies for this and other emotional disorders. However, until quite recently, there has been a large chasm between the practitioners and scientists working with this approach and those working on the neurobiological basis of depression and its treatment. Recent research, however, has started to bridge this gap and our understanding of the neural processes underpinning these cognitive processes has progressed markedly over the past decade. Moreover, rather than representing separate targets for psychological and biological treatments, novel findings suggest that pharmacological interventions for depression also modify these psychological maintaining factors early in treatment and may be involved in the later emergence of clinically relevant change. Such findings offer the possibility of greater integration between psychological and pharmacological conceptualisations of psychiatric illness and provide an experimental medicine model to generate and test specific predictions. Such a model could be applied to improve treatment development, stratification and combination approaches for patients with depression and provide a framework for considering and overcoming treatment nonresponse.