Effects of overshadowing on conditioned and unconditioned nausea in a rotation paradigm with humans

Antihistamines for motion sickness

BACKGROUND

Motion sickness is a syndrome that occurs as a result of passive body movement in response to actual motion, or the illusion of motion when exposed to virtual and moving visual environments. The most common symptoms are nausea and vomiting. Antihistamines have been used in the management of motion sickness for decades, however studies have shown conflicting results regarding their efficacy.

OBJECTIVES

To assess the effectiveness of antihistamines in the prevention and treatment of motion sickness in adults and children.

SEARCH METHODS

The Cochrane ENT Information Specialist searched the Cochrane ENT Register; Central Register of Controlled Trials; Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished trials. The date of the search was 7 December 2021.

SELECTION CRITERIA

Randomised controlled trials (RCTs) in susceptible adults and children in whom motion sickness was induced under natural conditions such as air, sea and land transportation. We also included studies in which motion sickness was induced under experimental conditions (analysed separately). Antihistamines were included regardless of class, route or dosage and compared to no treatment, placebo or any other pharmacological or non-pharmacological interventions.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were 1) the proportion of susceptible participants who did not experience any motion sickness symptoms; 2) the proportion of susceptible participants who experienced a reduction or resolution of existing symptoms. Secondary outcomes were 1) physiological measures (heart rate, core temperature and gastric tachyarrhythmia (electrogastrography)) and 2) adverse effects (sedation, impaired cognition, blurred vision). We used GRADE to assess the certainty of the evidence for each outcome.

MAIN RESULTS

We included nine RCTs (658 participants). Studies were conducted across seven countries, with an overall age range of 16 to 55 years. Motion sickness was induced naturally in six studies and experimentally in four studies (rotating chair). All the naturally induced studies only evaluated first-generation antihistamines (cinnarizine and dimenhydrinate). Risk of bias across the studies varied, with mostly low risk for random sequence generation and allocation concealment, and mostly high risk for selective reporting. Only the experimentally induced studies measured physiological parameters and only the naturally induced studies evaluated adverse effects. There were no studies that clearly assessed the paediatric population. Antihistamines versus placebo or no treatment Antihistamines are probably more effective than placebo at preventing motion sickness symptoms under natural conditions (symptoms prevented: 25% placebo; 40% antihistamines) (risk ratio (RR) 1.81, 95% confidence interval (CI) 1.23 to 2.66; 3 studies; 240 participants) (moderate-certainty). The evidence is very uncertain about the effect of antihistamines on preventing motion sickness under experimental conditions (standardised mean difference (SMD) 0.32, 95% CI -0.18 to 0.83; 2 studies; 62 participants) (very low-certainty). No studies reported results on the resolution of existing motion sickness symptoms. Antihistamines may result in little or no difference in gastric tachyarrhythmia under experimental conditions (mean difference (MD) -2.2, 95% CI -11.71 to 7.31; 1 study; 42 participants) (low-certainty). No studies reported results for any other physiological measures. When compared to placebo, antihistamines may be more likely to cause sedation (sedation: 44% placebo; 66% antihistamines) (RR 1.51, 95% CI 1.12 to 2.02; 2 studies; 190 participants) (low-certainty); they may result in little or no difference in blurred vision (blurred vision: 12.5% placebo; 14% antihistamines) (RR 1.14, 95% CI 0.53 to 2.48; 2 studies; 190 participants) (low-certainty); and they may result in little or no difference in terms of impaired cognition (impaired cognition: 33% placebo; 29% antihistamines) (RR 0.89, 95% CI 0.58 to 1.38; 2 studies; 190 participants) (low-certainty). Antihistamines versus scopolamine The evidence is very uncertain about the effect of antihistamines on preventing motion sickness under natural conditions when compared to scopolamine (symptoms prevented: 81% scopolamine; 71% antihistamines) (RR 0.89, 95% CI 0.68 to 1.16; 2 studies; 71 participants) (very low-certainty). No studies were performed under experimental conditions. No studies reported results on the resolution of existing motion sickness symptoms. The evidence is very uncertain about the effect of antihistamines on heart rate under natural conditions (narrative report, 1 study; 20 participants; "No difference in pulse frequency"; very low-certainty). No studies reported results for any other physiological measures. When compared to scopolamine, the evidence is very uncertain about the effect of antihistamines on sedation (sedation: 21% scopolamine; 30% antihistamines) (RR 0.82, 95% CI 0.07 to 9.25; 2 studies; 90 participants) (very low-certainty) and on blurred vision (narrative report: not a significant difference; 1 study; 51 participants; very low-certainty). No studies evaluated impaired cognition. Antihistamines versus antiemetics Antihistamines may result in little or no difference in the prevention of motion sickness under experimental conditions (MD -0.20, 95% CI -10.91 to 10.51; 1 study; 42 participants) (low-certainty). The evidence is of low certainty due to imprecision as the sample size is small and the confidence interval crosses the line of no effect. No studies assessed the effects of antihistamines versus antiemetics under natural conditions. No studies reported results on the resolution of existing motion sickness symptoms. Antihistamines may result in little or no difference in gastric tachyarrhythmia (MD 4.56, 95% CI -3.49 to 12.61; 1 study; 42 participants) (low-certainty). No studies reported results for any other physiological measures. No studies evaluated sedation, impaired cognition or blurred vision. One study reported physiological data for this outcome, evaluating gastric tachyarrhythmia specifically. Antihistamines may result in little or no difference in gastric tachyarrhythmia (MD 4.56, 95% CI -3.49 to 12.61; 1 study; 42 participants; low-certainty evidence). This evidence is of low certainty due to imprecision as the sample size is small and the confidence interval crosses the line of no effect. Antihistamines versus acupuncture The evidence is very uncertain about the effects of antihistamines on the prevention of motion sickness under experimental conditions when compared to acupuncture (RR 1.32, 95% CI 1.12 to 1.57; 1 study; 100 participants) (very low-certainty). This study did not assess the prevention of motion sickness under natural conditions, nor the resolution of existing motion sickness symptoms. There was no study performed under natural conditions. Physiological measures and adverse effects were not reported.

AUTHORS' CONCLUSIONS

There is probably a reduction in the risk of developing motion sickness symptoms under naturally occurring conditions of motion when using first-generation antihistamines, in motion sickness-susceptible adults, compared to placebo. Antihistamines may be more likely to cause sedation when compared to placebo. No studies evaluated the treatment of existing motion sickness, and there are few data on the effect of antihistamines in children. The evidence for all other outcomes and comparisons (versus scopolamine, antiemetics and acupuncture) was of low or very low certainty and we are therefore uncertain about these effects of antihistamines.

Pre-Exposure, But Not Overshadowing, Inhibits Nocebo Hyperalgesia

Nocebo hyperalgesia is a pervasive problem that significantly adds to the burden of pain. Conditioning is a key mechanism of nocebo hyperalgesia and recent evidence indicates that, once established, nocebo hyperalgesia is resistant to extinction. This means that preventive strategies are critical. We therefore tested whether two novel strategies - overshadowing (Experiment 1) and pre-exposure (Experiment 2) - could inhibit conditioned nocebo hyperalgesia. Overshadowing involves introducing additional cues during conditioning that should compete with and overshadow learning about the target nocebo cue. Pre-exposure involves pre-exposing the target nocebo cue in the absence of pain, which should diminish its ability to become associated with pain later. In both studies, healthy volunteers (N = 141) received exposure to a series of electrocutaneous pain stimuli with and without a sham electrode 'activated', which they were led to believe was a genuine hyperalgesic treatment. Nocebo conditioning was achieved by pairing sham activation with high pain prior to testing at equivalent pain intensity. In both studies, standard nocebo conditioning led to clear nocebo hyperalgesia relative to natural history controls. In Experiment 1, there was no evidence that overshadowing attenuated nocebo hyperalgesia. Importantly, however, Experiment 2 found that pre-exposure successfully attenuated nocebo hyperalgesia with post hoc analysis suggesting that this effect was dose-dependent. These findings provide novel evidence that pre-exposure, but not overshadowing, could be a cheap and effective way for mitigating the substantial harm caused by conditioned nocebo hyperalgesia in clinical settings. PERSPECTIVE: Nocebo hyperalgesia causes substantial patient burden with few preventive options available. Our study found novel evidence that pre-exposing treatment cues without pain, but not overshadowing them with other cues, has the capacity to inhibit conditioned nocebo hyperalgesia. Pre-exposure may therefore be an effective preventive strategy to combat nocebo hyperalgesia.

Cortico-Hippocampal Computational Modeling Using Quantum Neural Networks to Simulate Classical Conditioning Paradigms

Most existing cortico-hippocampal computational models use different artificial neural network topologies. These conventional approaches, which simulate various biological paradigms, can get slow training and inadequate conditioned responses for two reasons: increases in the number of conditioned stimuli and in the complexity of the simulated biological paradigms in different phases. In this paper, a cortico-hippocampal computational quantum (CHCQ) model is proposed for modeling intact and lesioned systems. The CHCQ model is the first computational model that uses the quantum neural networks for simulating the biological paradigms. The model consists of two entangled quantum neural networks: an adaptive single-layer feedforward quantum neural network and an autoencoder quantum neural network. The CHCQ model adaptively updates all the weights of its quantum neural networks using quantum instar, outstar, and Widrow–Hoff learning algorithms. Our model successfully simulated several biological processes and maintained the output-conditioned responses quickly and efficiently. Moreover, the results were consistent with prior biological studies.

Green model to adapt classical conditioning learning in the hippocampus

Compared with the biological paradigms of classical conditioning, non-adaptive computational models are not capable of realistically simulating the biological behavioural functions of the hippocampal regions, because of their implausible requirement for a large number of learning trials, which can be on the order of hundreds. Additionally, these models did not attain a unified, final stable state even after hundreds of learning trials. Conversely, the output response has a different threshold for similar tasks in various models with prolonged transient response of unspecified status via the training or even testing phases. Accordingly, a green model is a combination of adaptive neuro-computational hippocampal and cortical models that is proposed by adaptively updating the whole weights in all layers for both intact networks and lesion networks using instar and outstar learning rules with adaptive resonance theory (ART). The green model sustains and expands the classical conditioning biological paradigms of the non-adaptive models. The model also overcomes the irregular output response behaviour by using the proposed feature of adaptivity. Further, the model successfully simulates the hippocampal regions without passing the final output response back to the whole network, which is considered to be biologically implausible. The results of the Green model showed a significant improvement confirmed by empirical studies of different tasks. In addition, the results indicated that the model outperforms the previously published models. All the obtained results successfully and quickly attained a stable, desired final state (with a unified concluding state of either "1" or "0") with a significantly shorter transient duration.

Does Sex/Gender Play a Role in Placebo and Nocebo Effects? Conflicting Evidence From Clinical Trials and Experimental Studies

Sex has been speculated to be a predictor of the placebo and nocebo effect for many years, but whether this holds true or not has rarely been investigated. We utilized a placebo literature database on various aspects of the genuine placebo/nocebo response. In 2015, we had extracted 75 systematic reviews, meta-analyses, and meta-regressions performed in major medical areas (neurology, psychiatry, internal medicine). These meta-analyses were screened for whether sex/gender differences had been noted to contribute to the placebo/nocebo effect: in only 3 such analyses female sex was associated with a higher placebo effect, indicating poor evidence for a contribution of sex to it in RCTs. This was updated with another set of meta-analyses for the current review, but did not change the overall conclusion. The same holds true for 18 meta-analyses investigating adverse event (nocebo) reporting in RCT in the placebo arm of trials. We also screened our database for papers referring to sex/gender and the placebo effect in experimental studies, and identified 28 papers reporting 29 experiments. Their results can be summarized as follows: (a) Despite higher sensitivity of pain in females, placebo analgesia is easier to elicit in males; (b) It appears that conditioning is effective specifically eliciting nocebo effects; (c) Conditioning works specifically well to elicit placebo and nocebo effects in females and with nausea; (d) Verbal suggestions are not sufficient to induce analgesia in women, but work in men. These results will be discussed with respect to the question why nausea and pain may be prone to be responsive to sex/gender differences, while other symptoms are less. Lastly, we will discuss the apparent discrepancy between RCT with low relevance of sex, and higher relevance of sex in specific experimental settings. We argue that the placebo response is predominantly the result of a conditioning (learning) response in females, while in males it predominantly may be generated via (verbal) manipulating of expectancies. In RCT therefore, the net outcome of the intervention may be the same despite different mechanisms generating the placebo effect between the sexes, while in experimental work when both pathways are separated and explicitly explored, such differences may surface.

Placebo and Nocebo Effects Across Symptoms: From Pain to Fatigue, Dyspnea, Nausea, and Itch

Placebo and nocebo effects are, respectively, the helpful and harmful treatment effects that do not arise from active treatment components. These effects have thus far been researched most often in pain. It is not yet clear to what extent these findings from pain can be generalized to other somatic symptoms. This review investigates placebo and nocebo effects in four other highly prevalent symptoms: dyspnea, fatigue, nausea, and itch. The role of learning mechanisms (verbal suggestions, conditioning) in placebo and nocebo effects on various outcomes (self-reported, behavioral, and physiological) of these different somatic symptoms is explored. A search of experimental studies indicated that, as in pain, the combination of verbal suggestion and conditioning is generally more effective than suggestion alone for evoking placebo and nocebo effects. However, conditioning appears more and verbal suggestions less relevant in symptoms other than pain, with the exception of placebo effects on fatigue and nocebo effects on itch. Physiological measures, such as heart rate, lung function, or gastric activity, are rarely affected even when self-reported symptoms are. Neurobiological correlates are rarely investigated, and few commonalities appear across symptoms. Expectations generally predict placebo and nocebo effects for dyspnea and itch but seem less involved in fatigue and nausea. Individual characteristics do not consistently predict placebo or nocebo effects across symptoms or studies. In sum, many conclusions deriving from placebo and nocebo pain studies do appear to apply to other somatic symptoms, but a number of important differences exist. Understanding what type of learning mechanisms for which symptom are most likely to trigger placebo and nocebo effects is crucial for generalizing knowledge for research and therapies across symptoms and can help clinicians to optimize placebo effects in practice.

Novel designs and paradigms to study the placebo response in gastroenterology

The investigation of the placebo and the nocebo effect and their mechanisms has a rather short history of less than 20 years, especially in gastroenterology, and only the last 5 years have resulted in substantial improvement of understanding. Placebo refers to symptom improvement following a treatment, nocebo to the opposite, symptom worsening. Among the factors driving this progress are traditional psychological models derived from learning (conditioning) theory bridging into clinical science, new animal models to investigate the pharmacology of placebo analgesia, and novel study designs to overcome limitations of traditional randomized and placebo-controlled study designs in drug testing. These are explored here for their implementation and application in gastroenterology, with a focus on visceral pain and nausea.

Sex and Age Differences in Motion Sickness in Rats: The Correlation with Blood Hormone Responses and Neuronal Activation in the Vestibular and Autonomic Nuclei

Many studies have demonstrated sex and age differences in motion sickness, but the underlying physiological basis is still in controversy. In the present study, we tried to investigate the potential correlates of endocrine and/or neuronal activity with sex and age differences in rats with motion sickness. LiCl-induced nausea symptom was evaluated by conditioned gaping. Motion sickness was assessed by measurement of autonomic responses (i.e., conditioned gaping and defecation responses), motor impairments (i.e., hypoactivity and balance disturbance) after Ferris wheel-like rotation, and blood hormone levels and central Fos protein expression was also observed. We found that rotation-induced conditioned gaping, defecation responses and motor disorders were significantly attenuated in middle-aged animals (13- and 14-month-age) compared with adolescents (1- and 2-month-age) and young-adults (4- and/or 5-month-age). LiCl-induced conditioned gapings were also decreased with age, but was less pronounced than rotation-induced ones. Females showed greater responses in defecation and spontaneous locomotor activity during adolescents and/or young-adult period. Blood adrenocorticotropic hormone and corticosterone significantly increased in 4-month-old males after rotation compared with static controls. No significant effect of rotation was observed in norepinephrine, epinephrine, β-endorphin and arginine-vasopressin levels. The middle-aged animals (13-month-age) also had higher number of rotation-induced Fos-labeled neurons in the spinal vestibular nucleus, the parabrachial nucleus (PBN), the central and medial nucleus of amygdala (CeA and MeA) compared with adolescents (1-month-age) and young-adults (4-month-age) and in the nucleus of solitary tract (NTS) compared with adolescents (1-month-age). Sex difference in rotation-induced Fos-labeling was observed in the PBN, the NTS, the locus ceruleus and the paraventricular hypothalamus nucleus at 4 and/or 13 months of age. These results suggested that the sex and age differences in motion sickness may not correlate with stress hormone responses and habituation. The age-dependent decline in motion sickness susceptibility might be mainly attributed to the neuronal activity changes in vestibulo-autonomic pathways contributing to homeostasis regulation during motion sickness.

Different Disclosed Probabilities to Receive an Antiemetic Equally Decrease Subjective Symptoms in an Experimental Placebo Study: To Be or Not to Be Sure

PURPOSE

The purpose of this study was to examine whether the disclosed probability of receiving an antiemetic affects nausea.

METHODS

Forty-eight healthy participants (mean [SD] age, 26.8 [5.4] years; 50% female) were exposed to 5 × 2 minutes of nauseogenic body rotations on 2 days. On day 2, participants were randomized to 3 experimental groups that were given different instructions concerning the probability of receiving an antiemetic remedy (100%, 50%, or 0% probability), whereas all received an inert substance. Subjective symptoms, behavioral (rotation tolerance) measures, and physiologic (electrogastrogram) measures of nausea were assessed and mediator and moderator analyses performed for effects of expectations and psychological characteristics on outcomes.

FINDINGS

Disclosed probabilities of both 100% and 50% significantly reduced subjective symptoms of nausea in an equal manner compared with the 0% probability group from day 1 to day 2. This effect was found for neither rotation tolerance nor myoelectric gastric activity. Expectations and psychological characteristics did not affect the results found. Post hoc analyses revealed that women only seem to be susceptible to this placebo effect.

IMPLICATIONS

Nausea is susceptible to placebo effects independent of the disclosed probability of receiving a drug and of explicit expectations. In line with placebo research, this effect is probably attributable to central mechanisms, and it is speculated that it could be related to the reward circuitry and social interactions.

2016 updated MASCC/ESMO consensus recommendations: Anticipatory nausea and vomiting in children and adults receiving chemotherapy

PURPOSE

We aimed to update the 2011 recommendations for the prevention and treatment of anticipatory nausea and vomiting in children and adults receiving chemotherapy.

METHODS

The original systematic literature search was updated. Randomized studies were included in the evidence to support this guideline if they as follows: were primary studies published in a journal in full text (i.e., abstracts, letters, book chapters, and dissertations were excluded); published in English; evaluated an intervention for the prevention or treatment of anticipatory nausea and vomiting; reported the proportion of patients experiencing complete control of anticipatory nausea and vomiting consistently and; included at least ten participants per study arm for comparative studies and at least ten participants overall for noncomparative studies.

RESULTS

Eighty-eight new citations were identified. Of these, nine were brought to full-text screening; none met inclusion criteria. The guideline panel continues to recommend that anticipatory nausea and vomiting are best prevented through optimization of acute and delayed phase chemotherapy-induced nausea and vomiting control. Benzodiazepines and behavioral therapies, in particular progressive muscle relaxation training, systematic desensitization and hypnosis, continue to be recommended for the treatment of anticipatory nausea and vomiting.

CONCLUSIONS

No new information regarding interventions aimed at treating or preventing ANV that met criteria for inclusion in this systematic review was identified. The 2015 MASCC recommendations affirm the content of the 2009 MASCC recommendations for the prevention and treatment of anticipatory nausea and vomiting.

Overshadowing and latent inhibition in nausea-based context conditioning in humans: Theoretical and practical implications

Volunteer participants underwent nausea-inducing body rotation in a distinctive context, and the acquired ability of the contextual cues to evoke nausea was subsequently assessed by a symptom rating scale. One group received prior exposure to the context (a latent inhibition procedure); a second consumed a novel flavour prior to rotation (an overshadowing procedure); a third group experienced both procedures; and a control group received neither. When tested in the context in the absence of rotation, all groups reported an increase in nausea-related symptoms at the time when rotation had previously occurred, an outcome consistent with the occurrence of conditioned nausea. The magnitude of this increase did not differ across the groups, but the overall level of responsiveness (the degree to which nausea-related symptoms were reported) was enhanced in the latent inhibition and reduced in the overshadowing condition. Cortisol levels showed the same pattern. The implications of these findings for the proposal that overshadowing and latent inhibition procedures might be used to control the development of anticipatory nausea in patients undergoing chemotherapy is considered.

Sources of Placebo-Induced Relief From Nausea: The Role of Instruction and Conditioning

OBJECTIVES

It is well documented that expectancies alter the nauseous response. However, the lack of integration in research examining sources of expectancy has limited our understanding of how expectancies are formed and, consequently, our ability to intervene. The present study explored the role of both instructions and conditioning in placebo-induced relief from nausea.

METHODS

The study used a 2 × 2 between-subjects design with instruction and conditioning as factors with 56 healthy volunteers. The instruction manipulation involved randomizing participants to receive information that a sham treatment (a peppermint essence vapor) would reduce nausea or no such instructions. The conditioning manipulation involved further randomizing participants to have the first administration of this sham treatment paired with a surreptitious reduction in galvanic vestibular stimulation (GVS) intensity or no prior pairing. Nausea was induced through GVS. On test, all groups received the same level of GVS with the sham treatment present.

RESULTS

On test, participants who received instruction had significantly lower nauseous response scores than those who did not (F(1,46) = 6.71, p = .013), and those who received conditioning also reported less nausea than those who did not (F(1,46) = 5.20, p = .027), with the interaction between the two not reaching statistical significance (F(1,46) = 2.33, p = .13).

CONCLUSIONS

These findings indicate that placebo responding in nausea can be induced both through positive instructions and as little as one pairing of a treatment with a reduction in nausea, as well as their combination. This suggests that using placebo effects to complement antiemetic therapy may offer an important method of further reducing nausea in the clinic.

Neuro-Bio-Behavioral Mechanisms of Placebo and Nocebo Responses: Implications for Clinical Trials and Clinical Practice

The placebo effect has often been considered a nuisance in basic and particularly clinical research. This view has gradually changed in recent years due to deeper insight into the neuro-bio-behavioral mechanisms steering both the placebo and nocebo responses, the evil twin of placebo. For the neuroscientist, placebo and nocebo responses have evolved as indispensable tools to understand brain mechanisms that link cognitive and emotional factors with symptom perception as well as peripheral physiologic systems and end organ functioning. For the clinical investigator, better understanding of the mechanisms driving placebo and nocebo responses allow the control of these responses and thereby help to more precisely define the efficacy of a specific pharmacological intervention. Finally, in the clinical context, the systematic exploitation of these mechanisms will help to maximize placebo responses and minimize nocebo responses for the patient's benefit. In this review, we summarize and critically examine the neuro-bio-behavioral mechanisms underlying placebo and nocebo responses that are currently known in terms of different diseases and physiologic systems. We subsequently elaborate on the consequences of this knowledge for pharmacological treatments of patients and the implications for pharmacological research, the training of healthcare professionals, and for the health care system and future research strategies on placebo and nocebo responses.

Placebo effects and their determinants in gastrointestinal disorders

Placebo effects in clinical trials have sparked an interest in the placebo phenomenon, both in randomized controlled trials (RCTs) and in experimental gastroenterology. RCTs have demonstrated similar short-term and long-term placebo response rates in gastrointestinal compared to other medical diagnoses. Most mediators and moderators of placebo effects in gastrointestinal diseases are also of similar type and size to other medical diagnoses and not specific for gastrointestinal diagnoses. Other characteristics such as an increase in the placebo response over time and the placebo-enhancing effects of unbalanced randomization were not seen, at least in IBS. Experimental placebo and nocebo studies underscore the 'power' of expectancies and conditioning processes in shaping gastrointestinal symptoms not only at the level of self-reports, but also within the brain and along the brain-gut axis. Brain imaging studies have redressed earlier criticism that placebo effects might merely reflect a response bias. These findings raise hope that sophisticated trials and experiments designed to boost positive expectations and minimize negative expectations could pave the way for a practical and ethically sound use of placebo knowledge in daily practice. Rather than focusing on a 'personalized' choice of drugs based on biomarkers or genes, it might be the doctor-patient communication that needs to be tailored.