Test-retest reliability of pain-related functional brain connectivity compared with pain self-report

To Calibrate or not to Calibrate? A Methodological Dilemma in Experimental Pain Research

To calibrate or not to calibrate? This question is raised by almost everyone designing an experimental pain study with supra-threshold stimulation. The dilemma is whether to individualize stimulus intensity to the pain threshold / supra-threshold pain level of each participant or whether to provide the noxious stimulus at a fixed intensity so that everyone receives the identical input. Each approach has unique pros and cons which need to be considered to i) accurately design an experiment, ii) enhance statistical inference in the given data and, iii) reduce bias and the influence of confounding factors in the individual study e.g., body composition, differences in energy absorption and previous experience. Individualization requires calibration, a procedure already irritating the nociceptive system but allowing to match the pain level across individuals. It leads to a higher variability of the stimulus intensity, thereby influencing the encoding of "noxiousness" by the central nervous system. Results might be less influenced by statistical phenomena such as ceiling/floor effects and the approach does not seem to rise ethical concerns. On the other hand, applying a fixed (standardized) intensity reduces the problem of intensity encoding leading to a large between-subjects variability in pain responses. Fixed stimulation intensities do not require pre-exposure. It can be proposed that one method is not preferable over another, however the choice depends on the study aim and the desired level of external validity. This paper discusses considerations for choosing the optimal approach for experimental pain studies and provides recommendations for different study designs. PERSPECTIVE: To calibrate pain or not? This dilemma is related to almost every experimental pain research. The decision is a trade-off between statistical power and greater control of stimulus encoding. The article decomposes both approaches and presents the pros and cons of either approach supported by data and simulation experiment.

Neuroimaging Assessment of Pain

Pain is an unpleasant sensory and emotional experience. Understanding the neural mechanisms of acute and chronic pain and the brain changes affecting pain factors is important for finding pain treatment methods. The emergence and progress of non-invasive neuroimaging technology can help us better understand pain at the neural level. Recent developments in identifying brain-based biomarkers of pain through advances in advanced imaging can provide some foundations for predicting and detecting pain. For example, a neurologic pain signature (involving brain regions that receive nociceptive afferents) and a stimulus intensity-independent pain signature (involving brain regions that do not show increased activity in proportion to noxious stimulus intensity) were developed based on multivariate modeling to identify processes related to the pain experience. However, an accurate and comprehensive review of common neuroimaging techniques for evaluating pain is lacking. This paper reviews the mechanism, clinical application, reliability, strengths, and limitations of common neuroimaging techniques for assessing pain to promote our further understanding of pain.

Comparison of test–retest reliability of BOLD and pCASL fMRI in a two-center study

Background

The establishment of test–retest reliability and reproducibility (TRR) is an important part of validating any research tool, including functional magnetic resonance imaging (fMRI). The primary objective of this study is to investigate the reliability of pseudo-Continuous Arterial Spin Labeling (pCASL) and Blood Oxygen Level Dependent (BOLD) fMRI data acquired across two different scanners in a sample of healthy adults. While single site/single scanner studies have shown acceptable repeatability, TRR of both in a practical multisite study occurring in two facilities spread out across the country with weeks to months between scans is critically needed.

Methods

Ten subjects were imaged with similar 3 T MRI scanners at the University of Pittsburgh and Massachusetts General Hospital. Finger-tapping and Resting-state data were acquired for both techniques. Analysis of the resting state data for functional connectivity was performed with the Functional Connectivity Toolbox, while analysis of the finger tapping data was accomplished with FSL. pCASL Blood flow data was generated using AST Toolbox. Activated areas and networks were identified via pre-defined atlases and dual-regression techniques. Analysis for TRR was conducted by comparing pCASL and BOLD images in terms of Intraclass correlation coefficients, Dice Similarity Coefficients, and repeated measures ANOVA.

Results

Both BOLD and pCASL scans showed strong activation and correlation between the two locations for the finger tapping tasks. Functional connectivity analyses identified elements of the default mode network in all resting scans at both locations. Multivariate repeated measures ANOVA showed significant variability between subjects, but no significant variability for location. Global CBF was very similar between the two scanning locations, and repeated measures ANOVA showed no significant differences between the two scanning locations.

Conclusions

The results of this study show that when similar scanner hardware and software is coupled with identical data analysis protocols, consistent and reproducible functional brain images can be acquired across sites. The variability seen in the activation maps is greater for pCASL versus BOLD images, as expected, however groups maps are remarkably similar despite the low number of subjects. This demonstrates that multi-site fMRI studies of task-based and resting state brain activity is feasible.

Effect sizes and test-retest reliability of the fMRI-based neurologic pain signature

Identifying biomarkers that predict mental states with large effect sizes and high test-retest reliability is a growing priority for fMRI research. We examined a well-established multivariate brain measure that tracks pain induced by nociceptive input, the Neurologic Pain Signature (NPS). In N = 295 participants across eight studies, NPS responses showed a very large effect size in predicting within-person single-trial pain reports (d = 1.45) and medium effect size in predicting individual differences in pain reports (d = 0.49). The NPS showed excellent short-term (within-day) test-retest reliability (ICC = 0.84, with average 69.5 trials/person). Reliability scaled with the number of trials within-person, with ≥60 trials required for excellent test-retest reliability. Reliability was tested in two additional studies across 5-day (N = 29, ICC = 0.74, 30 trials/person) and 1-month (N = 40, ICC = 0.46, 5 trials/person) test-retest intervals. The combination of strong within-person correlations and only modest between-person correlations between the NPS and pain reports indicate that the two measures have different sources of between-person variance. The NPS is not a surrogate for individual differences in pain reports but can serve as a reliable measure of pain-related physiology and mechanistic target for interventions.

Training endogenous pain modulation: a preliminary investigation of neural adaptation following repeated exposure to clinically-relevant pain

Analgesic treatments that aim to eliminate pain display marginal success in relieving chronic pain and may increase pain vulnerability. Repeated exposure to pain may result in increased pain modulation via engagement of anti-nociceptive brain regions. It was hypothesized that repeated exposure to delayed onset muscle soreness (DOMS) would result in increased pain modulatory capacity (PMC) via functional neural adaptation. 23 healthy participants completed Baseline and Follow Up resting-state fMRI and quantitative sensory testing (QST) visits 40 days apart. Participants were randomized to two groups: A Repeated DOMS Group (RD Group) that received four, weekly DOMS inductions and a Control Group that received one baseline induction. Daily pain ratings were collected for seven days post-induction, as were quantitative sensory testing (QST) metrics at baseline and Follow Up. Regional functional connectivity (FC) was estimated among areas involved in pain modulation. Seed and network FC was estimated among areas involved in pain modulation and sensory processing. Changes in FC were compared between groups. The RD Group displayed significant reductions in post-DOMS pain ratings and significant changes in thermal QST measures. RD Group participants displayed greater adaptation in nucleus accumbens-medial prefrontal cortex (NAc-mPFC) FC and in sensorimotor network (SMN) connectivity with the dorsomedial, ventromedial, and rostromedial prefrontal cortices. Changes in SMN-PFC connectivity correlated with reductions in post-DOMS affective distress. Results suggest that repeated exposure to clinically-relevant pain results in adaptations among brain regions involved in pain modulation. Repeated exposure to clinically-relevant pain may serve as a mechanism to increase PMC via inhibition of emotional valuation of painful stimuli.

Spatial and Frequency-specific Electrophysiological Signatures of Tonic Pain Recovery in Humans

The objective of this study was to comprehensively investigate patterns of brain activities associated with pain recovery following experimental tonic pain in humans. Specific electrophysiological features of pain recovery may either be monitored or be modulated through neurofeedback (NF) as a novel chronic pain treatment. The cold pressor test was applied with simultaneous electroencephalogram (EEG) recording. EEG data were acquired, and analyzed to define: (1) EEG power topography patterns of pain recovery; (2) source generators of pain recovery at cortical level; (3) changes in functional connectivity associated with pain recovery; (4) features of phase-amplitude coupling (PAC) as it relates to pain recovery. The novel finding of this study is that recovery from pain was characterized by significant theta power rebound at the left fronto-central area. The sources of theta power over-recovery were located in the left dorsolateral prefrontal cortex (DLPFC), cingulate cortex, left insula and contralateral sensorimotor cortex. These effects were paralleled by theta band connectivity increase within hemispheres in a prefrontal-somatosensory network and interhemispherically between prefrontal and parietal areas. In addition, this study revealed significant reduction in PAC between theta/alpha and gamma oscillations during recovery period following tonic pain. These findings have largely been replicated across two identical sessions. Our study emphasizes the association between pain recovery and left lateral prefrontal theta power rebound, and significant over-recovery of functional connectivity in prefrontal-sensorimotor neural network synchronized at theta frequencies. These findings may provide basis for chronic pain treatment by modulating neural oscillations at theta frequencies in left prefrontal cortex.

Intrinsic Connectivity Networks in the Self- and Other-Referential Processing

Neuroimaging studies have revealed a multitude of brain regions associated with self- and other-referential processing, but the question how the distinction between self, close other, and distant other is processed in the brain still remains unanswered. The default mode network (DMN) is the primary network associated with the processing of self, whereas task-positive networks (TPN) are indispensable for the processing of external objects. We hypothesize that self- and close-other-processing would engage DMN more than TPN, whereas distant-other-processing would engage TPN to a greater extent. To test this hypothesis, we used functional magnetic resonance imaging (fMRI) functional connectivity data obtained in the course of a trait adjective judgment task while subjects evaluated themselves, the best friend, a neutral stranger, and an unpleasant person. A positive association between the degree of self-relatedness and the degree of DMN dominance was revealed in cortical midline structures (CMS) and the left lateral prefrontal cortex. Relative to TPN, DMN showed greater connectivity in me than in friend, in friend than in stranger, and in stranger than in unpleasant conditions. These results show that the less the evaluated person is perceived as self-related, the more the balance of activity in the brain shifts from the DMN to the TPN.

Re-test reliability and internal consistency of EEG alpha-band oscillations in older adults with chronic knee pain

OBJECTIVE

Chronic pain studies investigating the ability to detect sensory processing differences related to thalamic gating using electroencephalographic (EEG) alpha have yielded conflicting results. Alpha's basic psychometric properties in pain populations requires further study. The present study reports on the test-retest reliability and internal consistency of EEG alpha power in older adults with chronic knee pain.

METHODS

Repeated EEG alpha power measurements were taken of older adults (N = 31) with chronic knee pain across two sessions separated by a ten-day period associated with a pilot clinical trial study. Recordings included resting periods (eyes open and eyes closed) as well as periods involving a pain management activity.

RESULTS

Most single alpha-power measures and all within-participant averages of alpha obtained within a session showed high internal consistency (Cronbach's α > 0.7) and satisfactory-to-excellent re-test reliability (Pearson's rs > 0.6) of both alpha power and alpha blocking (eyes closed minus eyes open) across repeated conditions.

CONCLUSIONS

EEG alpha power seems mostly reliable and consistent, particularly when participants' eyes are closed, after a period of habituation, and when alpha measures are averaged as within-participant estimates.

SIGNIFICANCE

This analysis suggests that within-subject averages of EEG alpha are the most reliable for developing indices of chronic knee pain.

Noxious pressure stimulation demonstrates robust, reliable estimates of brain activity and self-reported pain

Functional neuroimaging techniques have provided great insight in the field of pain. Utilising these techniques, we have characterised pain-induced responses in the brain and improved our understanding of key pain-related phenomena. Despite the utility of these methods, there remains a need to assess the test retest reliability of pain modulated blood-oxygen-level-dependant (BOLD) MR signal across repeated sessions. This is especially the case for more novel yet increasingly implemented stimulation modalities, such as noxious pressure, and it is acutely important for multi-session studies considering treatment efficacy. In the present investigation, BOLD signal responses were estimated for noxious-pressure stimulation in a group of healthy participants, across two separate sessions. Test retest reliability of functional magnetic resonance imaging (fMRI) data and self-reported visual analogue scale measures were determined by the intra-class correlation coefficient. High levels of reliability were observed in several key brain regions known to underpin the pain experience, including in the thalamus, insula, somatosensory cortices, and inferior frontal regions, alongside "excellent" reliability of self-reported pain measures. These data demonstrate that BOLD-fMRI derived signals are a valuable tool for quantifying noxious responses pertaining to pressure stimulation. We further recommend the implementation of pressure as a stimulation modality in experimental applications.

Acute Alcohol Intake Produces Widespread Decreases in Cortical Resting Signal Variability in Healthy Social Drinkers

BACKGROUND

Acute alcohol intoxication has wide-ranging neurobehavioral effects on psychomotor, attentional, inhibitory, and memory-related cognitive processes. These effects are mirrored in disruption of neural metabolism, functional activation, and functional network coherence. Metrics of intraregional neural dynamics such as regional signal variability (RSV) and brain entropy (BEN) may capture unique aspects of neural functional capacity in healthy and clinical populations; however, alcohol's influence on these metrics is unclear. The present study aimed to elucidate the influence of acute alcohol intoxication on RSV and to clarify these effects with subsequent BEN analyses.

METHODS

26 healthy adults between 25 and 45 years of age (65.4% women) participated in 2 counterbalanced sessions. In one, participants consumed a beverage containing alcohol sufficient to produce a breath alcohol concentration of 0.08 g/dl. In the other, they consumed a placebo beverage. Approximately 35 minutes after beverage consumption, participants completed a 9-minute resting-state fMRI scan. Whole-brain, voxel-wise standard deviation was used to assess RSV, which was compared between sessions. Within clusters displaying alterations in RSV, sample entropy was calculated to assess BEN.

RESULTS

Compared to the placebo, alcohol intake resulted in widespread reductions in RSV in the bilateral middle frontal, right inferior frontal, right superior frontal, bilateral posterior cingulate, bilateral middle temporal, right supramarginal gyri, and bilateral inferior parietal lobule. Within these clusters, significant reductions in BEN were found in the bilateral middle frontal and right superior frontal gyri. No effects were noted in subcortical or cerebellar areas.

CONCLUSIONS

Findings indicate that alcohol intake produces diffuse reductions in RSV among structures associated with attentional processes. Within these structures, signal complexity was also reduced in a subset of frontal regions. Neurobehavioral effects of acute alcohol consumption may be partially driven by disruption of intraregional neural dynamics among regions involved in higher-order cognitive and attentional processes.

Exploring the potential role of mesocorticolimbic circuitry in motivation for and adherence to chronic pain self-management interventions

Adherence to pain self-management strategies is associated with favorable psychobehavioral outcomes among individuals with chronic pain. Substantive adherence to treatments teaching these adaptive skills often proves challenging, resulting in poor individual and societal outcomes. Evidence demonstrates motivation for behavior change as a key predictor of treatment adherence. Despite behavioral techniques that target motivation, however, nonadherence persists as a barrier to positive clinical outcomes in chronic pain. Understanding the neurobiological mechanisms underlying treatment motivation might highlight novel avenues for augmentative therapies. The purpose of this review is to present theory and evidence that the mesocorticolimbic system (i.e., brain circuitry associated with reward processing and motivation) contributes to treatment motivation among chronic pain patients, ultimately influencing adherence. We review evidence for motivation as a key adherence determinant, detail neuroimaging findings relating mesocorticolimbic circuitry and motivation, and discuss data supporting mesocorticolimbic dysfunction among chronic pain patients. We propose a neurobehavioral model for adherence to pain self-management interventions, listing testable hypotheses. Finally, we discuss potential research and intervention implications from the proposed model.

Worsen depression after viscosupplementation treatment for geriatric people with knee osteoarthritis?

Background/objective: Knee osteoarthritis (OA) in older people may result in psychological impairment, including anxiety and depression. This study investigates the effect of intraarticular hyaluronic acid injection (IAHA) on geriatric patients with OA. Method: A total of 102 geriatric patients with knee OA undergoing IAHA were prospectively enrolled in this study. Geriatric Depression Scale (GDS), State-Trait Anxiety Inventory (STAI), Western Ontario and McMaster University Osteoarthritis Index (WOMAC) and the International Knee Documentation Committee Subjective Knee Evaluation Form (IKDC), and Visual Analogue Scale (VAS) for pain were recorded. All outcomes were measured at baseline before injection and during two, four, and six month follow-ups. Results: IAHA had a significant short-term effect, relieving pain at the two month follow-up, but the effect was weaker at the four month follow-up. Both IKDC and WOMAC scores were significantly improved at the two month follow-up. Viscosupplementation did not improve STAI. GDS exhibited significant deterioration at the four month follow-up. Conclusions: Although IAHA for the treatment of OA provided short-term efficiency, it had no effects on anxiety and increased depression of geriatric people. Health education should be provided with caution before viscosupplementation treatment to manage expectations of the efficacy of treatment for geriatric OA patients.

Detectability and reproducibility of the olfactory fMRI signal under the influence of magnetic susceptibility artifacts in the primary olfactory cortex

For human olfactory functional MRI studies, the primary olfactory cortex (POC) suffers severe magnetic susceptibility artifacts, which adversely influences the detectability and reproducibility of the olfactory fMRI data and its clinical applications. The goal of this work is to assess the impacts of the image artifacts on the detectability and reproducibility of the olfactory activation in the POC. The severity of artifacts in the POC were classified into three levels using a Subjective Artifact score (SA_score). The mean temporal signal-to-noise ratio (tSNR) of the fMRI data acquired by a given MRI sequence and olfactory activation (β value) in POC were evaluated and compared to the concurrent activations in the primary visual cortex (Brodmann area 17, BA17) by an odor-visual association paradigm using ninety-nine normal human subjects. Our study revealed that the mean tSNR in POC was above the threshold for reliable detection of the functional activation signal, and, consequently, the mean olfactory activations in the POC were not significantly different from those in BA17. The reproducibility of the activation in the POC was assessed by a random half-split stimulation of a test-retest experiment. The overlap of the activation maps for all the trials (n = 1000) in the POC were not statistically different from that observed in BA17. These results show that the detectability and reproducibility of olfactory activation in the presence of susceptibility artifacts in the POC was at similar level of that in the visual cortex.

Effects of Educational Intervention on State Anxiety and Pain in People Undergoing Spinal Surgery: A Randomized Controlled Trial

Preoperative educational intervention for anxiety and pain affects patients undergoing spinal surgery. The effects, however, have never been examined using randomized controlled designs. To investigate the effects of education on anxiety and pain for patients undergoing spinal surgery, a randomized trial with block design was used. Patients were recruited from a medical center in central Taiwan. We invited 90 patients to participate in this study. Inclusion criteria were (a) age ≥20 years, (b) voluntary participation, (c) able to understand Taiwanese Mandarin Chinese or Taiwanese, and (4) no hearing or vision impairments after using aids. Patients (n = 86) undergoing lumbar spinal surgery were randomized into either an Intervention group (using educational intervention; n = 43) or a Control group (n = 43); four patients voluntarily dropped out after surgery (one in Intervention group; three in Control group). Patients had their anxiety (using the State-Trait Anxiety Inventory; STAI) and pain (using a visual analog scale) measured the day before surgery, 30 minutes before surgery, and the day after surgery. After controlling for demographics, the adjusted anxiety and pain levels were significantly lower for the Intervention group: mean STAI scores were 52.67 at baseline and 47.54 at 30 minutes before surgery (p < .001); mean pain scores were 6.07 at baseline and 5.28 on day after surgery (p < .001). Preoperative educational intervention is effective in informing patients undergoing spinal surgery that can lead to a reduction in pain, anxiety, and fear postoperatively.

Biomarkers for Musculoskeletal Pain Conditions: Use of Brain Imaging and Machine Learning

Chronic musculoskeletal pain condition often shows poor correlations between tissue abnormalities and clinical pain. Therefore, classification of pain conditions like chronic low back pain, osteoarthritis, and fibromyalgia depends mostly on self report and less on objective findings like X-ray or magnetic resonance imaging (MRI) changes. However, recent advances in structural and functional brain imaging have identified brain abnormalities in chronic pain conditions that can be used for illness classification. Because the analysis of complex and multivariate brain imaging data is challenging, machine learning techniques have been increasingly utilized for this purpose. The goal of machine learning is to train specific classifiers to best identify variables of interest on brain MRIs (i.e., biomarkers). This report describes classification techniques capable of separating MRI-based brain biomarkers of chronic pain patients from healthy controls with high accuracy (70-92%) using machine learning, as well as critical scientific, practical, and ethical considerations related to their potential clinical application. Although self-report remains the gold standard for pain assessment, machine learning may aid in the classification of chronic pain disorders like chronic back pain and fibromyalgia as well as provide mechanistic information regarding their neural correlates.