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.

Oscillatory EEG activity induced by conditioning stimuli during fear conditioning reflects Salience and Valence of these stimuli more than Expectancy.

Imaging studies have described hemodynamic activity during fear conditioning protocols with stimulus trains in which a visual conditioned stimulus (CS+) is paired with an aversive unconditioned stimulus (US, painful laser pulse) while another visual stimulus is unpaired (CS-). We now test the hypothesis that CS Event Related Spectral Perturbations (ERSPs) are related to ratings of CS Expectancy (likelihood of pairing with the US), Valence (unpleasantness) and Salience (ability to capture attention). ERSP windows in EEG were defined by both time after the CS and frequency, and showed increased oscillatory power (Event Related Synchronization, ERS) in the Delta/Theta Windows (0-8Hz) and the Gamma Window (30-55Hz). Decreased oscillatory power (Event Related Desynchronization - ERD) was found in Alpha (8-14Hz) and Beta Windows (14-30Hz). The Delta/Theta ERS showed a differential effect of CS+ versus CS- at Prefrontal, Frontal and Midline Channels, while Alpha and Beta ERD were greater at Parietal and Occipital Channels early in the stimulus train. The Gamma ERS Window increased from habituation to acquisition over a broad area from frontal and occipital electrodes. The CS Valence and Salience were greater for CS+ than CS-, and were correlated with each other and with the ERD at overlapping channels, particularly in the Alpha Window. Expectancy and CS Skin Conductance Response were greater for CS+ than CS- and were correlated with ERSP at fewer channels than Valence or Salience. These results suggest that Alpha ERSP activity during fear conditioning reflects Valence and Salience of the CSs more than conditioning per se.

The placebo effect: From concepts to genes.

Despite its initial treatment as a nuisance variable, the placebo effect is now recognized as a powerful determinant of health across many different diseases and encounters. This is in light of some remarkable findings ranging from demonstrations that the placebo effect significantly modulates the response to active treatments in conditions such as pain, anxiety, Parkinson's disease, and some surgical procedures. Here, we review pioneering studies and recent advances in behavioral, neurobiological, and genetic influences on the placebo effect. Consistent with recent conceptualizations, the placebo effect is presented as the product of a general expectancy learning mechanism in which verbal, conditioned, and social cues are centrally integrated to change behaviors and outcomes. Examples of the integration of verbal and conditioned cues, such as instructed reversal of placebo effects are also incorporated into this model. We discuss neuroimaging studies that have identified key brain regions and modulatory mechanisms underlying placebo effects using well-established behavioral paradigms. Finally, we present a synthesis of recent genetics studies on the placebo effect, highlighting a promising link between genetic variants in the dopamine, opioid, serotonin, and endocannabinoid pathways and placebo responsiveness. Greater understanding of the behavioral, neurobiological, and genetic influences on the placebo effect is critical for evaluating medical interventions and may allow health professionals to tailor and personalize interventions in order to maximize treatment outcomes in clinical settings.

Socially induced placebo analgesia: a comparison of a pre-recorded versus live face-to-face observation.

BACKGROUND: Recently, it has been shown that live, face-to-face social observation induces marked placebo analgesia. Despite the phenomenal growth of video sharing platforms, the potential analgesic effects of video-based social observation are largely unknown. This study compared video-based and live social observation induced placebo analgesia and whether there was a similar relationship between analgesic responses and empathy traits for both conditions. METHODS: Here, we compared placebo analgesia in four groups: social observation through a video (SOV group), social observation in person (SOP group), verbal suggestion alone (VS group) and a natural history group (NH group). The SOV and SOP groups underwent a placebo treatment and painful stimuli following respectively a video-based and live observation of a demonstrator showing analgesic effects when the painful stimuli were paired to a green light but not a red light. The VS group received painful stimuli after they had been verbally instructed to expect less pain after the green light. The NH group received painful stimuli, but was told nothing about the meaning of the lights. Individual pain reports and empathy traits were measured. RESULTS: We found that video-based observation induced substantial placebo analgesic responses that were of similar magnitude to live observation. Notably, the analgesic scores were strongly correlated with empathetic concern in the live observation group but not in the video replay group. CONCLUSIONS: These findings add evidence that placebo analgesia can be induced by social observation and that empathy interacts with these effects in a context-dependent manner.

Probable REM sleep behaviour disorder and STN-DBS outcome in Parkinson's Disease.

OBJECTIVE: To assess whether the presence of probable REM sleep behaviour disorder (pRBD) influences the long-term outcome of Parkinson's Disease (PD) patients undergoing Subthalamic Nucleus Deep Brain Stimulation (STN-DBS). BACKGROUND: RBD is a parasomnia characterized by loss of muscular atonia and complex motor behaviours during REM sleep, frequently reported in PD patients. Recent evidence suggests that RBD is associated with akinetic rigid disease type and increased frequency of falls. We wondered whether the presence of RBD would also influence the long-term outcome of STN-DBS. METHODS: Forty-one consecutive PD patients treated with bilateral STN-DBS were assessed. The diagnosis of pRBD was based on a clinical interview investigating the occurrence of diagnostic criteria for RBD. The Unified Parkinson's Disease Rating Scale was used to compare the on- and off-medication conditions preoperatively and the on-stimulation/on- and off-medication conditions 1 and 3 years postoperatively. The general linear model for multivariate measures was used to analyse the interaction of pRBD with STN-DBS outcome measures. RESULTS: pRBD was present in 12 out of 41 patients (29%) undergoing STN-DBS. Patients with pRBD had a significantly poorer outcome three years after STN-DBS compared to patients without pRBD, in particular for axial symptoms. CONCLUSIONS: Our findings suggest that the presence of pRBD in PD patients undergoing STN-DBS may be associated with a less favourable outcome and a more prominent development of axial symptoms over time.

The role of learning in nocebo and placebo effects.

The nocebo effect consists in delivering verbal suggestions of negative outcomes so that the subject expects clinical worsening. Here we show that nocebo suggestions, in which expectation of pain increase is induced, are capable of producing both hyperalgesic and allodynic responses. By extending previous findings on the placebo effect, we investigated the role of learning in the nocebo effect by means of a conditioning procedure. To do this, verbal suggestions of pain increase were given to healthy volunteers before administration of either tactile or low-intensity painful electrical stimuli. This nocebo procedure was also carried out after a pre-conditioning session in which two different conditioned visual stimuli were associated to either pain or no-pain. Pain perception was assessed by means of a Numerical Rating Scale raging from 0=tactile to 10=maximum imaginable pain. We found that verbal suggestions alone, without prior conditioning, turned tactile stimuli into pain as well as low-intensity painful stimuli into high-intensity pain. A conditioning procedure produced similar effects, without significant differences. Therefore, in contrast to placebo analgesia, whereby a conditioning procedure elicits larger effects compared to verbal suggestions alone, learning seems to be less important in nocebo hyperalgesia. Overall, these findings indicate that, by defining hyperalgesia as an increase in pain sensitivity and allodynia as the perception of pain in response to innocuous stimulation, nocebos can indeed produce both hyperalgesic and allodynic effects. These results also suggest that learning is not important in nocebo hyperalgesia compared to placebo analgesia.

When words are painful: unraveling the mechanisms of the nocebo effect.

The nocebo effect is a phenomenon that is opposite to the placebo effect, whereby expectation of a negative outcome may lead to the worsening of a symptom. Thus far, its study has been limited by ethical constraints, particularly in patients, as a nocebo procedure is per se stressful and anxiogenic. It basically consists in delivering verbal suggestions of negative outcomes so that the subject expects clinical worsening. Although some natural nocebo situations do exist, such as the impact of negative diagnoses upon the patient and the patient's distrust in a therapy, the neurobiological mechanisms have been understood in the experimental setting under strictly controlled conditions. As for the placebo counterpart, the study of pain has been fruitful in recent years to understand both the neuroanatomical and the neurochemical bases of the nocebo effect. Recent experimental evidence indicates that negative verbal suggestions induce anticipatory anxiety about the impending pain increase, and this verbally-induced anxiety triggers the activation of cholecystokinin (CCK) which, in turn, facilitates pain transmission. CCK-antagonists have been found to block this anxiety-induced hyperalgesia, thus opening up the possibility of new therapeutic strategies whenever pain has an important anxiety component. Other conditions, such as Parkinson's disease, although less studied, have been found to be affected by nocebo suggestions as well. All these findings underscore the important role of cognition in the therapeutic outcome, and suggest that nocebo and nocebo-related effects might represent a point of vulnerability both in the course of a disease and in the response to a therapy.