Wacław Adamczyk

Classical conditioning without verbal suggestions elicits placebo analgesia and nocebo hyperalgesia.

The aim of this study was to examine the relationships among classical conditioning, expectancy, and fear in placebo analgesia and nocebo hyperalgesia. A total of 42 healthy volunteers were randomly assigned to three groups: placebo, nocebo, and control. They received 96 electrical stimuli, preceded by either orange or blue lights. A hidden conditioning procedure, in which participants were not informed about the meaning of coloured lights, was performed in the placebo and nocebo groups. Light of one colour was paired with pain stimuli of moderate intensity (control stimuli), and light of the other colour was paired with either nonpainful stimuli (in the placebo group) or painful stimuli of high intensity (in the nocebo group). In the control group, both colour lights were followed by control stimuli of moderate intensity without any conditioning procedure. Participants rated pain intensity, expectancy of pain intensity, and fear. In the testing phase, when both of the coloured lights were followed by identical moderate pain stimuli, we found a significant analgesic effect in the placebo group, and a significant hyperalgesic effect in the nocebo group. Neither expectancy nor fear ratings predicted placebo analgesia or nocebo hyperalgesia. It appears that a hidden conditioning procedure, without any explicit verbal suggestions, elicits placebo and nocebo effects, however we found no evidence that these effects are predicted by either expectancy or fear. These results suggest that classical conditioning may be a distinct mechanism for placebo and nocebo effects.

Lumbar Tactile Acuity in Patients With Low Back Pain and Healthy Controls: Systematic Review and Meta-Analysis

Objective: Diminished tactile acuity in chronic non-neuropathic pain syndromes has been attributed to central pain processing and cortical reorganization. The latter was recently targeted in clinical trials that demonstrated no clear advantages over traditional approaches for the reduction of nonspecific low back pain (LBP). The aim of this systematic review and meta-analysis was to summarize the current evidence on tactile acuity in LBP and pain-free controls. Methods: Six databases were independently searched by 2 researchers. Nineteen studies with either case-control, cross-sectional, or baseline lumbar tactile acuity data collected before an intervention were included in the qualitative and quantitative synthesis. All pooled analyses were based on random effects models. Risk of bias was assessed using the Downs and Black scale and selection criteria were verified independently by 2 assessors. Results: Data on patients (n=547) and controls (n=346) were summarized. Studies on patients included data on nonspecific chronic LBP only; no data on acute LBP were identified. There was a significant mean difference between patients and controls for lumbar tactile acuity including (11.74 mm; 95% confidence interval, 8.61-14.87) and excluding (9.49 mm; 95% confidence interval, 3.64-15.34) higher risk of bias studies. Discussion: A gap of knowledge regarding tactile acuity in populations with acute and chronic non-neuropathic LBP needs to be addressed in future research as this may significantly help the understanding of the causality of tactile acuity alterations.

Tactile acuity (dys)function in acute nociceptive low back pain: a double-blind experiment

Abstract Research shows that chronic pain is related to cortical alterations that can be reflected in reduced tactile acuity, but whether acute pain perception influences tactile acuity has not been tested. Considering the biological role of nociception, it was hypothesized that nociceptive pain will lead to a rapid improvement in tactile acuity and that this effect is correlated with pain intensity and pain distribution. In this randomised double-blind controlled experiment (trial no. NCT03021278), healthy participants were exposed to 1 of 3 experimental conditions: acute, nociceptive low back pain induced by saline injection, a sham injection (without piercing the skin) potentially inducing nocebo pain, or no intervention. Tactile acuity was measured by a battery of tests, including two-point discrimination threshold (TPD), before, during the pain experience, and after it subsided. We found that TPD did not improve but deteriorated during pain induction in the experimental group compared with the control group (P < 0.001; &eegr;2 = 0.20) and changed from 56.94 mm (95% confidence interval: 53.43-60.44) at baseline to 64.22 mm (95% confidence interval: 60.42-68.02) during the pain experience. Maximum reported pain was a significant predictor (&bgr; = 0.55, P = 0.01) and accounted for 26% of the variance in TPD (P < 0.05). Other tests, point-to-point test and two-point estimation task, changed with a similar trend but did not reach significance. We concluded that acute, nociceptive pain does not improve but deteriorates tactile acuity linearly. The biological role of the observed phenomenon is unknown, and therefore, future studies should address this question.

How Classical Conditioning Shapes Placebo Analgesia: Hidden versus Open Conditioning

Objective To investigate the influence of expectancy of pain intensity, fear of pain (trait), and fear (state) on the effectiveness of hidden and open conditioning to produce placebo analgesia. Methods A total of 90 healthy female volunteers were randomly assigned to three groups (hidden conditioning, open conditioning, and control) that received electrical stimuli preceded by either orange or blue lights. One color was paired with painful stimuli (control stimuli) and the other color was paired with nonpainful stimuli (conditioned stimuli) in both the hidden and open conditioning groups. Only participants in the open conditioning group were informed about this association. In the control group, both color lights were followed by control stimuli. In the testing phase, both colored lights were followed by identical control stimuli. Participants rated pain intensity, expectancy of pain intensity, fear, and fear of pain. Results A significant analgesic effect was found only in the hidden conditioning group, where no explicit verbal suggestions were provided. Hidden conditioning had an effect on expectancy and fear-participants in the hidden conditioning group expected less pain and experienced less fear in relation to conditioned stimuli. Fear was the only predictor of placebo analgesia in the hidden conditioning group. Neither expectancy of pain intensity nor fear of pain predicted placebo analgesia. Conclusions Fear seems to be a more important factor than expectancy in producing placebo analgesia induced by hidden conditioning.

Pain rewarded: hyperalgesic and allodynic effect of operant conditioning in healthy humans-protocol for a systematic review and meta-analysis.

Background‘Pain rewarded’ is a hypothesis wherein acute pain sufferers are exposed to reinforcers and punishers from their environment that shape their behaviour, i.e. pain responses. Such a point of view has been taken for granted by many clinicians and researchers although existing evidence has not yet been systematically summarized. This planned systematic review and meta-analysis is aiming to summarize the research findings on pain modulation (hyperalgesic effect) and pain elicitation (allodynic effect) resulting from operant conditioning procedures in healthy humans.MethodsThe systematic review will be performed by searching for articles indexed in PubMed database, Cochrane Register of Controlled Trials (CENTRAL), Web of Science™, ScienceDirect, EBSCO database, PsycINFO, MEDLINE, PsycARTICLES and CINAHL. Studies will be included if they investigate healthy humans, exposed to modulation or elicitation of a pain experience induced by operant conditioning. Studies will be screened for eligibility and risk of bias by two independent assessors. Narrative and meta-analytical syntheses are planned.DiscussionData will be pooled and analyzed qualitatively and quantitatively (if possible) in order to advance the understanding of pain mechanisms, especially the development of chronic pain. This systematic review will guide the planning of future experiments and research by summarizing important technical details of conditioning procedures in healthy humans.Systematic review registrationPROSPERO CRD42017051763

Sensory dissociation in chronic low back pain: Two case reports

ABSTRACT Patients with chronic low back pain often report that they do not perceive their painful back accurately. Previous studies confirmed that sensory dissociation and/or discrepancy between perceived body image and actual size is one of the specific traits of patients with chronic pain. Current approaches for measuring sensory dissociation are limited to two-point-discrimination or rely on pain drawings not allowing for quantitative analysis. This case study reports the sensory dissociation of two cases with chronic low back pain using a recently published test (point-to-point-test (PTP)) and a newly developed test (two-point-estimation (TPE)). Both patients mislocalized tactile stimuli delivered to the painful location compared to non-painful locations (PTP test). In addition, both patients perceived their painful lumbar region differently from non-painful sites above and below and contralateral to the painful site. TPE data showed two distinct clinical patterns of sensory dissociation: one patient perceived the two-point distance in the painful area as expanded, while the other patient perceived it as shrunk. The latter pattern of sensory dissociation (i.e., pattern shrunk) is likely to respond to sensory training. Whether enlarged patterns of sensory dissociation are more resistant to treatment remains unknown but would explain the low effectiveness of previous studies using sensory training in chronic low back pain populations. Subgrouping patients according to their sensory discrimination pattern could contribute to the choice and effectiveness of the treatment approach.

Comment on Castien et al. (2018) pressure pain thresholds over the cranio-cervical region in headache - a systematic review and meta-analysis

The recently published systematic review by Castien et al. [1] is summarising data in a field of highly ambiguous reporting. Pain thresholds in headache patients have been investigated by a large number of researchers with inconsistent results and it is certainly important to summarise and evaluate all data in a systematic review and meta-analysis. However, the present review can only partially shed light on the issue, due to a number of rather grave methodological shortcomings. The underlying concept is, that especially the two primary headache types, TTH and migraine, show a component of (peripheral or central) sensitization. There are two major difficulties for researchers trying to clarify the presence or absence of sensitization:

Upper cervical two-point discrimination thresholds in migraine patients and headache-free controls

BackgroundChronic pain including migraine is associated with structural and functional changes in the somatosensory cortex. Previous reports proposed two-point discrimination (TPD) as a measurement for cortical alterations. Limited evidence exists for tactile acuity in the neck and no data is available for migraine.MethodsTo introduce a standardized protocol for the measurement of TPD in the upper cervical spine, 51 healthy participants were investigated with a newly developed paradigm which was evaluated for intra-rater reliability. The same protocol was applied by two further examiners to 28 migraine patients and 21 age-, and gender-matched healthy controls to investigate inter-rater reliability and between group differences.ResultsResults indicated excellent intra-rater (right ICC(2,4) = 0.82, left ICC(2,4) = 0.83) and good inter-rater reliability (right ICC(2,4) = 0.70, left ICC(2,4) = 0.75). Migraine patients had larger TPD thresholds (26.86 ± 7.21) than healthy controls (23.30 ± 6.17) but these became only statistically significant for the right side of the neck (p = 0.02). There was a significant, moderate association with age for the right side (r = 0.42 p = 0.002, n = 51), and less strong association for the left side (r = 0.34, p = 0.14) in healthy individuals. TPD did not correlate with headache days per month or the dominant headache side in migraine patients.ConclusionsSurprisingly, migraine patients showed increased TPD thresholds in the upper cervical spine interictally. Although a body of evidence supports that hypersensitivity is part of the migraine attack, the current report indicates that interictally, migraine patients showed worse tactile acuity similar to other chronic pain populations. This has been hypothesized to indicate structural and functional re-organisation of the somatosensory cortex.

Pain begets pain: When marathon runners are not in pain anymore, they underestimate their memory of marathon pain: A mediation analysis

A previous study has shown that memory of pain induced by running a marathon might be underestimated. However, little is known about the factors that might influence such a memory distortion during pain recall. The aim of the study was to investigate the memory of pain induced by running a marathon and the factors that might influence it: (1) present pain during recall and (2) recall delay.

Tissue Deformation Index as a Reliable Measure of Lateral Abdominal Muscle Activation on M-Mode Sonography

The aim of this article is to present a novel method of evaluating the activity of lateral abdominal muscles using M‐mode sonography. The method leads to calculation of the tissue deformation index, representing the percent change in lateral abdominal muscle thickness over time. The objectives of this study were as follows: (1) to establish the mean tissue deformation index values for individual lateral abdominal muscles; and (2) to establish the reliability of the tissue deformation index. In a group of 34 healthy young volunteers (mean age, 24.03 years; body mass, 68.89 kg; body height, 174.25 cm), the reflex response of the lateral abdominal muscles to postural perturbation in the form of rapid arm abduction was recorded in 2 series, with 6 repetitions each, and the tissue deformation index was calculated. The mean tissue deformation index values formed a gradient, increasing from deep to superficial lateral abdominal muscles: 0.06%/ms for transversus abdominis, 0.11%/ms for oblique internal, and 0.16 for oblique external muscles. The tissue deformation index values differed significantly among individual lateral abdominal muscles (all paired comparisons, P < .001). Three repeated measurements are sufficient to achieve good intra‐rater reliability of the tissue deformation index (intraclass correlation coefficient, > 0.8).