Biased Intensity Judgements of Visceral Sensations After Learning to Fear Visceral Stimuli: A Drift Diffusion Approach

The influence of a manipulation of threat on experimentally-induced secondary hyperalgesia

Pain is thought to be influenced by the threat value of the particular context in which it occurs. However, the mechanisms by which a threat achieves this influence on pain are unclear. Here, we explore how threat influences experimentally-induced secondary hyperalgesia, which is thought to be a manifestation of central sensitization. We developed an experimental study to investigate the effect of a manipulation of threat on experimentally-induced secondary hyperalgesia in 26 healthy human adults (16 identifying as female; 10 as male). We induced secondary hyperalgesia at both forearms using high-frequency electrical stimulation. Prior to the induction, we used a previously successful method to manipulate threat of tissue damage at one forearm (threat site). The effect of the threat manipulation was determined by comparing participant-rated anxiety, perceived threat, and pain during the experimental induction of secondary hyperalgesia, between the threat and control sites. We hypothesized that the threat site would show greater secondary hyperalgesia (primary outcome) and greater surface area (secondary outcome) of induced secondary hyperalgesia than the control site. Despite a thorough piloting procedure to test the threat manipulation, our data showed no main effect of site on pain, anxiety, or threat ratings during high-frequency electrical stimulation. In the light of no difference in threat between sites, the primary and secondary hypotheses cannot be tested. We discuss reasons why we were unable to replicate the efficacy of this established threat manipulation in our sample, including: (1) competition between threats, (2) generalization of learned threat value, (3) safety cues, (4) trust, and requirements for participant safety, (5) sampling bias, (6) sample-specific habituation to threat, and (7) implausibility of (sham) skin examination and report. Better strategies to manipulate threat are required for further research on the mechanisms by which threat influences pain.

Cortico-Brainstem Mechanisms of Biased Perceptual Decision-Making in the Context of Pain

Prior expectations can bias how we perceive pain. Using a drift diffusion model, we recently showed that this influence is primarily based on changes in perceptual decision-making (indexed as shift in starting point). Only during unexpected application of high-intensity noxious stimuli, altered information processing (indexed as increase in drift rate) explained the expectancy effect on pain processing. Here, we employed functional magnetic resonance imaging to investigate the neural basis of both these processes in healthy volunteers. On each trial, visual cues induced the expectation of high- or low-intensity noxious stimulation or signaled equal probability for both intensities. Participants categorized a subsequently applied electrical stimulus as either low- or high-intensity pain. A shift in starting point towards high pain correlated negatively with right dorsolateral prefrontal cortex activity during cue presentation underscoring its proposed role of "keeping pain out of mind". This anticipatory right dorsolateral prefrontal cortex signal increase was positively correlated with periaqueductal gray (PAG) activity when the expected high-intensity stimulation was applied. A drift rate increase during unexpected high-intensity pain was reflected in amygdala engagement and increased functional connectivity between amygdala and PAG. Our findings suggest involvement of the PAG in both decision-making bias and altered information processing to implement expectancy effects on pain. PERSPECTIVE: Modulation of pain through expectations has been linked to changes in perceptual decision-making and altered processing of afferent information. Our results suggest involvement of the dorsolateral prefrontal cortex, amygdala, and periaqueductal gray in these processes.

Temporal dynamics of fMRI signal changes during conditioned interoceptive pain-related fear and safety acquisition and extinction

Associative learning and memory mechanisms drive interoceptive signaling along the gut-brain axis, thus shaping affective-emotional reactions and behavior. Specifically, learning to predict potentially harmful, visceral pain is assumed to succeed within very few trials. However, the temporal dynamics of cerebellar and cerebral fMRI signal changes underlying early acquisition and extinction of learned fear signals and the concomitant evolvement of safety learning remain incompletely understood. 3T fMRI data of healthy individuals from three studies were uniformly processed across the whole brain and the cerebellum including an advanced normalizing method of the cerebellum. All studies employed differential delay conditioning (N=94) with one visual cue (CS⁺) being repeatedly paired with visceral pain as unconditioned stimulus (US) while a second cue remained unpaired (CS^-). During subsequent extinction (N=51), all CS were presented without US. Behavioral results revealed increased CS⁺-aversiveness and CS^--pleasantness after conditioning and diminished valence ratings for both CS following extinction. During early acquisition, the CS^- induced linearly increasing neural activation in the insula, midcingulate cortex, hippocampus, precuneus as well as cerebral and cerebellar somatomotor regions. The comparison between acquisition and extinction phases yielded a CS^--induced linear increase in the posterior cingulate cortex and precuneus during early acquisition, while there was no evidence for linear fMRI signal changes for the CS⁺ during acquisition and for both CS during extinction. Based on theoretical accounts of discrimination and temporal difference learning, these results suggest a gradual evolvement of learned safety cues that engage emotional arousal, memory, and cortical modulatory networks. As safety signals are presumably more difficult to learn and to discriminate from learned threat cues, the underlying temporal dynamics may reflect enhanced salience and prediction processing as well as increasing demands for attentional resources and the integration of multisensory information. Maladaptive responses to learned safety signals are a clinically relevant phenotype in multiple conditions, including chronic visceral pain, and can be exceptionally resistant to modification or extinction. Through sustained hypervigilance, safety seeking constitutes one key component in pain and stress-related avoidance behavior, calling for future studies targeting the mechanisms of safety learning and extinction to advance current cognitive-behavioral treatment approaches.

When experience is not enough: learning-based cognitive pain modulation with or without instructions

ABSTRACT

The effects of expectations on pain perception are often studied using large differences in pain probabilities between experimental conditions, although they may be far more subtle in clinical contexts and, therefore, more difficult to detect. The current study aimed to investigate at which point subtle differences in pain probabilities can be detected and lead to differentiable expectations and perceptions. Furthermore, we investigated whether instructions can aid learning from experience and enhance subsequent pain modulatory effects. During a predictive learning task, participants were presented with 5 different cues, followed by either a high and low noxious stimulus. They learned about the different cue-stimulus contingencies either solely through experience (LEARN, N = 40) or a combination of experience and explicit information about the cue-stimulus contingencies (INSTRUCT, N = 40). We found that without explicit information, picking up the different pain probabilities was challenging, while explicit instruction significantly improved their detection. As revealed by drift diffusion modeling, learning from experience was insufficient for the development of a bias towards low pain even when it was highly likely. By contrast, when explicit information was provided, perception became more nuanced with the direction and extent of bias, capturing the subtle differences in pain probabilities. These findings highlight that the use of instructions to foster the detection of subtle pain improvements during pain treatment to enhance their cognitive pain modulatory effects warrant further investigation.

Esophageal hypervigilance is prevalent across gastroesophageal reflux disease presentations

BACKGROUND

There is a need to identify factors outside of abnormal reflux that contribute to gastroesophageal reflux disease (GERD). Esophageal hypervigilance is a psychological process impacting symptom experience in esophageal disease. However, little is known about the presence of hypervigilance in GERD phenotypes, especially in those with abnormal acid exposure or symptom index scores. The primary aim was to assess differences in self-reported esophageal hypervigilance across different GERD presentations. The secondary aim was to evaluate esophageal hypervigilance as a predictor of symptom severity.

METHODS

We conducted retrospective data analyses on a cohort of adult patients with reflux symptoms that underwent 96-hour wireless pH monitoring from 9/2015 to 9/2017. Patients were stratified into groups based on the number of days they exhibited positive acid exposure time (AET; 0 days, 1-2 days, 3+ days), and symptom index scores (SI; 0 days, 1-day, 2+ days). Esophageal hypervigilance and anxiety, and symptom frequency and severity were assessed between groups.

KEY RESULTS

A total of 123 AET cases and 116 SI cases were included for analysis. Esophageal hypervigilance and anxiety scores did not significantly differ based on the number of days of positive AET (p = 0.311) or SI (p = 0.118). Symptom severity and perceived symptom frequency differed between groups. Hypervigilance significantly predicted symptom severity, when controlling for symptom-specific anxiety.

CONCLUSIONS

Esophageal hypervigilance is persistent across patients with reflux, irrespective of acid burden and symptom index, and significantly predicts symptom severity. Hypervigilance should be considered as an independent factor contributing to esophageal symptom perception.

Perceptual variability: Implications for learning and generalization

The generalization of learned behavior has been extensively investigated, but accounting for variance in generalized responding remains a challenge. Based on recent advances, we demonstrate that the inclusion of perceptual measures in generalization research may lead to a better understanding of both intra- and interindividual differences in generalization. We explore various ways through which perceptual variability can influence generalized responding. We investigate its impact on the ability to discriminate between stimuli and how similarity between stimuli may be variable, rather than fixed, because of it. Subsequently, we argue that perceptual variations can yield different learning experiences and that interindividual differences in generalized responding may be understood from this perspective. Finally, we point to the role of memory and decision-making within this context. Throughout this paper, we argue that accounting for perception in current generalization protocols will improve the precision of obtained generalization gradients and the ability to infer latent mechanisms. This can inspire future attempts to use generalization gradients as a (clinical) predictor or to relate them to individual traits and neural correlates and, ultimately, may lead to new theoretical and clinical insights.

Pain can be conditioned to voluntary movements through associative learning: an experimental study in healthy participants

Experimental data suggest that associative learning can influence defensive avoidance behavior and pain perception in humans. However, whether voluntary movements can become conditioned stimuli (CSs) and influence pain responses is yet to be evaluated. Forty healthy volunteers participated in this study. Electrocutaneous stimuli applied to the shoulder at pain threshold level (US) and at pain tolerance level (US) were determined before a movement-conditioning paradigm. First, reaching movements to visual cues shown on one side of a computer screen were associated with the US (CS+ movements) on 80% of trials, whereas reaching movements to visual stimuli shown on the other side were never associated with the nociceptive-US (CS- movements). Next, participants underwent a test phase in which movements to visual cues on both sides were paired with the US on 50% of trials. During the test phase, participants were asked to evaluate whether the movement was painful (yes/no) and to rate pain intensity after each trial. Movement onset and duration as well as skin conductance responses were collected. The US stimuli were more likely to be perceived as painful and were also rated as more painful during CS+ movements. Movement onset latency and skin conductance responses were significantly higher in anticipation of the CS+ movement as compared to the CS- movement. These findings suggest that pain can be conditioned to voluntary movements.

The use of stimulus perception to account for variability in skin conductance responses to interoceptive stimuli

Activity of the electrodermal response system is customarily expressed in relation to physical stimulus properties and not to perceived features. In situations where the delivery of physically identical stimuli can be challenging, such as in interoception research, this variability might pose a challenge for contemporary SCR analyses. Therefore, we investigated the extent to which activity in the electrodermal response system triggered by the delivery of interoceptive stimuli is better predicted by perceived intensity rather than physical input. For this purpose, we reanalyzed data from the baseline phase of a previous study (n = 60) in which skin conductance responses (SCRs) to innocuous esophageal stimulations of high and low intensities were recorded in addition to categorizations based on their perceived intensity (high or low). Using both peak scoring and model inversion methods, we found that the inclusion of stimulus perception as a predictor of the magnitude of the SCR increased model fit. These findings suggest that the inclusion of perception is a promising avenue to better model variability in psychophysiological responses to interoceptive stimuli.

The Influence of Pain-Related Expectations on Intensity Perception of Nonpainful Somatosensory Stimuli

OBJECTIVE

The extent to which pain-related expectations, known to affect pain perception, also affect perception of nonpainful sensations remains unclear, as well as the potential role of unpredictability in this context.

METHODS

In a proprioceptive fear conditioning paradigm, various arm extension movements were associated with predictable and unpredictable electrocutaneous pain or its absence. During a subsequent test phase, nonpainful electrocutaneous stimuli with a high or low intensity were presented during movement execution. We used hierarchical drift diffusion modeling to examine the influence of expecting pain on the perceptual decision-making process underlying intensity perception of nonpainful sensations. In the first experiment (n = 36), the pain stimulus was never presented during the test phase after conditioning. In the second experiment (n = 39), partial reinforcement was adopted to prevent extinction of pain expectations.

RESULTS

In both experiments, movements that were associated with (un)predictable pain led to higher pain expectancy, self-reported fear, unpleasantness, and arousal as compared with movements that were never paired with pain (effect sizes η2 ranging from 0.119 to 0.557; all p values < .05). Only in the second experiment-when the threat of pain remained present-we found that the expectation of pain affected decision making. Compared with the no pain condition, an a priori decision-making bias toward the high-intensity decision threshold was found with the strongest bias during unpredictable pain (effect sizes η2 ranging from 0.469 to 0.504; all p-values < .001).

CONCLUSIONS

Thus, the expectation of pain affects inferential processes not only for subsequent painful but also for nonpainful bodily stimuli, with unpredictability moderating these effects, and only when the threat of pain remains present due to partial reinforcement.

The gut-brain axis in health neuroscience: implications for functional gastrointestinal disorders and appetite regulation

Over the past few years, scientific interest in the gut-brain axis (i.e., the bidirectional communication system between the gastrointestinal tract and the brain) has exploded, mostly due to the identification of the gut microbiota as a novel key player in this communication. However, important progress has also been made in other aspects of gut-brain axis research, which has been relatively underemphasized in the review literature. Therefore, in this review, we provide a comprehensive, although not exhaustive, overview of recent research on the functional neuroanatomy of the gut-brain axis and its relevance toward the multidisciplinary field of health neuroscience, excluding studies on the role of the gut microbiota. More specifically, we first focus on irritable bowel syndrome, after which we outline recent findings on the role of the gut-brain axis in appetite and feeding regulation, primarily focusing on the impact of subliminal nutrient-related gut-brain signals. We conclude by providing future perspectives to facilitate translation of the findings from gut-brain axis neuroscientific research to clinical applications in these domains.

Direct and indirect effects of perception on generalization gradients

For more than a century, researchers have attempted to understand why organisms behave similarly across situations. Despite the robust character of generalization, considerable variation in conditioned responding both between and within humans remains a challenge for contemporary generalization models. The current study aims to investigate the extent to which variation in behavior in a context of generalization can be attributed to differences in perception. We combined a fear conditioning and generalization procedure with a perceptual decision task in humans. We found that the failure to perceive a novel stimulus as different from the trained fear-evoking stimulus led to increased conditioned responding. Furthermore, perceptual errors yielded perceived stimulus-outcome contingencies that differed substantially from the objective contingencies. Final, the impact of a perceptual error was dependent upon these perceived contingencies. These findings suggest that generalization across a perceptual dimension is to a large extent driven by perceptual errors that directly affect behavior but also indirectly as they yield different learning experiences between individuals.

Biogastronomy: Factors that determine the biological response to meal ingestion

BACKGROUND

The biological response to a meal includes physiological changes, primarily related to the digestive process, and a sensory experience, involving sensations related to the homeostatic control of food consumption, eg, satiety and fullness, with a hedonic dimension, ie associated with changes in digestive well-being and mood. The responses to a meal include a series of events before, during and after ingestion. While much attention has been paid to the events before and during ingestion, relatively little is known about the postprandial sensations, which are key to the gastronomical experience.

PURPOSE

The aim of this narrative review is to provide a comprehensive overview and to define the framework to investigate the factors that determine the postprandial experience. Based on a series of proof-of-concept studies and related information, we propose that the biological responses to a meal depend on the characteristics of the meal, primarily its palatability and composition, and the responsiveness of the guest, which may be influenced by multiple previous and concurrent conditioning factors. This information provides the scientific backbone to the development of personalized gastronomy.