Multiple Brain Networks Mediating Stimulus-Pain Relationships in Humans

Caloric labels do not influence taste pleasantness and neural responses to erythritol and sucrose

INTRODUCTION

The beneficial effects of substituting sugar with non-caloric sweeteners (NCSs) remain uncertain due to the mismatch between their rewarding sweet taste and lack of energy content. Functional magnetic resonance imaging (fMRI) studies indicate an influence of cognitive processes (e.g., beliefs, expectations) on reward system responses to NCSs, thereby changing their rewarding properties. We measured the impact of cognitive influences about the caloric content on brain responses and liking ratings to erythritol, a natural NCS with satiating properties, versus sugar (i.e., sucrose).

METHODS

We performed a within-subject, single-blind, counterbalanced fMRI study in 30 healthy males (mean ± SD: age 23 ± 0.6 years, BMI 22.5 ± 0.3 kg/m²). Concentrations of erythritol were individually titrated to match the perceived sweetness intensity of a 16 % sucrose solution. During the scan, sucrose and equisweet erythritol solutions were delivered as 1 mL sips with either correct or purposefully incorrect "low-calorie" or "high-calorie" labels. After each sip, participants rated sweetness liking. Water with a "water" label was used as the control condition.

RESULTS

A 2 × 2 ANOVA revealed lower liking ratings for erythritol than sucrose (p < 0.0001), but no main effect of the label, nor label-by-sweetener interaction. General Linear Model (GLM) analysis of brain responses at FDR q < 0.05 showed no main effect of sweetener nor label, nor a label-by-sweetener interaction. However, several patterns of brain activity mediated the differences in subjective liking ratings between the sweeteners. Moreover, different neural responses were found for sucrose vs. water in parcel-wise, SVM, and ROI-based analyses, whereas for erythritol vs. water, only the latter two showed differences. Lastly, sucrose induced a stronger craving signature response compared to erythritol, driven by the pattern specific to drug craving.

CONCLUSION

Liking ratings were lower for erythritol than sucrose, and they were unaffected by the caloric label. There were no differences in neural responses between the sweeteners and labels, except in comparisons with water.

Zero-echo time imaging achieves whole brain activity mapping without ventral signal loss in mice

Functional MRI (fMRI) is an important tool for investigating functional networks. However, the widely used fMRI with T2*-weighted imaging in rodents has the problem of signal lack in the lateral ventral area of forebrain including the amygdala, which is essential for not only emotion but also noxious pain. Here, we scouted the zero-echo time (ZTE) sequence, which is robust to magnetic susceptibility and motion-derived artifacts, to image activation in the whole brain including the amygdala following the noxious stimulation to the hind paw. ZTE exhibited higher temporal signal-to-noise ratios than conventional fMRI sequences. Electrical sensory stimulation of the hind paw evoked ZTE signal increase in the primary somatosensory cortex. Formalin injection into the hind paw evoked early and latent change of ZTE signals throughout the whole brain including the subregions of amygdala. Furthermore, resting-state fMRI using ZTE demonstrated the functional connectivity, including that of the amygdala. These results indicate the feasibility of ZTE for whole brain fMRI including the amygdala and we first show acute and latent activity in different subnuclei of the amygdala complex after nociceptive stimulation.

Music and hypnosis for well-being in retirement homes: A pilot study

Anxiety, pain and poor well-being are major issues in elderly individuals. Complementary interventions, such as music and hypnosis, are increasingly used to address these issues. The objectives of this study were to assess immediate changes in anxiety, pain and well-being during personalized prerecorded music and hypnosis interventions compared to control sessions, and to explore participants' subjective experiences. We employed a multiple time series model with daily measurements with older people living in retirement homes in rural areas (n = 8). The Edmonton Symptom Assessment Scale (ESAS) evaluated these three dimensions before and after each session, while participants' subjective experience was collected using an unstructured interview. The primary results showed a significant improvement in the composite score of anxiety, pain, and well-being for the music (p < .001), hypnosis (p = .0158), and music/hypnosis (p = .013) intervention sessions compared to the control sessions. The secondary results indicated a reduction in anxiety for both the music and music/hypnosis interventions (p < .05), along with a significant improvement in well-being. These effects may be attributed to mechanisms such as absorption, episodic memory, cognitive agency, positive emotion, rhythmic entrainment, and rapport, which could have modulated the interventions' impact. In conclusion, personalized prerecorded music and hypnosis interventions appear to be effective in enhancing the well-being of older individuals residing in retirement homes. Further studies are needed to assess the generalizability of these results to a larger population from diverse sociodemographic backgrounds, and better understand the subjective experiences that mediate these effects.

Information search under uncertainty across transdiagnostic psychopathology and healthy ageing

When making decisions in everyday life, we often rely on an internally generated sense of confidence to help us revise and direct future behaviours. For instance, confidence directly informs whether further information should be sought prior to commitment to a final decision. Many studies have shown that aging and both clinical and sub-clinical symptoms of psychopathology are associated with systematic alterations in confidence. However, it remains unknown whether these confidence distortions influence information-seeking behaviour. We investigated this question in a large general population sample (N = 908). Participants completed a battery of psychiatric symptom questionnaires and performed a perceptual decision-making task with confidence ratings in which they were offered the option to seek helpful information (at a cost) before committing to a final decision. Replicating previous findings, an 'anxious-depression' (AD) symptom dimension was associated with systematically low confidence, despite no detriment in objective task accuracy. Conversely, a 'compulsive behaviour and intrusive thoughts' (CIT) dimension was associated with impaired task accuracy but paradoxical over-confidence. However, neither symptom dimension was significantly associated with an increased or decreased tendency to seek information. Hence, participants scoring highly for AD or CIT did not use the option to information seek any more than average to either increase their confidence (AD) or improve the accuracy of their decisions (CIT). In contrast, older age was associated with impaired accuracy and decreased confidence initially, but increased information seeking behaviour mediated increases in both accuracy and confidence for final decisions. Hence, older adults used the information seeking option to overcome initial deficits in objective performance and to increase their confidence accordingly. The results show an appropriate use of information seeking to overcome perceptual deficits and low confidence in healthy aging which was not present in transdiagnostic psychopathology.

Neural responses to oral administration of erythritol vs. sucrose and sucralose explain differences in subjective liking ratings

INTRODUCTION

High sugar intake is associated with many chronic diseases. However, non-caloric sweeteners (NCSs) might fail to successfully replace sucrose due to the mismatch between their rewarding sweet taste and lack of caloric content. The natural NCS erythritol has been proposed as a sugar substitute due to its satiating properties despite being non-caloric. We aimed to compare brain responses to erythritol vs. sucrose and the artificial NCS sucralose in a priori taste, homeostatic, and reward brain regions of interest (ROIs).

METHODS

We performed a within-subject, single-blind, counterbalanced fMRI study in 30 healthy men (mean ± SEM age:24.3 ± 0.8 years, BMI:22.3 ± 0.3 kg/m2). Before scanning, we individually matched the concentrations of both NCSs to the perceived sweetness intensity of a 10% sucrose solution. During scanning, participants received 1 mL sips of the individually titrated equisweet solutions of sucrose, erythritol, and sucralose, as well as water. After each sip, they rated subjective sweetness liking.

RESULTS

Liking ratings were significantly higher for sucrose and sucralose vs. erythritol (both pHolm = 0.0037); water ratings were neutral. General Linear Model (GLM) analyses of brain blood oxygen level-depended (BOLD) responses at qFDR<0.05 showed no differences between any of the sweeteners in a priori ROIs, but distinct differences were found between the individual sweeteners and water. These results were confirmed by Bayesian GLM and machine learning-based models. However, several brain response patterns mediating the differences in liking ratings between the sweeteners were found in whole-brain multivariate mediation analyses. Both subjective and neural responses showed large inter-subject variability.

CONCLUSION

We found lower liking ratings in response to oral administration of erythritol vs. sucrose and sucralose, but no differences in neural responses between any of the sweeteners in a priori ROIs. However, differences in liking ratings between erythritol vs. sucrose or sucralose are mediated by multiple whole-brain response patterns.

Controlling false discovery rate for mediator selection in high-dimensional data

The need to select mediators from a high dimensional data source, such as neuroimaging data and genetic data, arises in much scientific research. In this work, we formulate a multiple-hypothesis testing framework for mediator selection from a high-dimensional candidate set, and propose a method, which extends the recent development in false discovery rate (FDR)-controlled variable selection with knockoff to select mediators with FDR control. We show that the proposed method and algorithm achieved finite sample FDR control. We present extensive simulation results to demonstrate the power and finite sample performance compared with the existing method. Lastly, we demonstrate the method for analyzing the Adolescent Brain Cognitive Development (ABCD) study, in which the proposed method selects several resting-state functional magnetic resonance imaging connectivity markers as mediators for the relationship between adverse childhood events and the crystallized composite score in the NIH toolbox.

Presynaptic inhibition of excitatory synaptic transmission from the calcitonin gene-related peptide-containing parabrachial neurons to the central amygdala in mice - unexpected influence of systemic inflammation thereon

The monosynaptic connection from the lateral parabrachial nucleus (LPB) to the central amygdala (CeA) serves as a fundamental pathway for transmitting nociceptive signals to the brain. The LPB receives nociceptive information from the dorsal horn and spinal trigeminal nucleus and sends it to the "nociceptive" CeA, which modulates pain-associated emotions and nociceptive sensitivity. To elucidate the role of densely expressed mu-opioid receptors (MORs) within this pathway, we investigated the effects of exogenously applied opioids on LPB-CeA synaptic transmission, employing optogenetics in mice expressing channelrhodopsin-2 in LPB neurons with calcitonin gene-related peptide (CGRP). A MOR agonist ([D-Ala2,N-Me-Phe4,Glycinol5]-enkephalin, DAMGO) significantly reduced the amplitude of light-evoked excitatory postsynaptic currents (leEPSCs), in a manner negatively correlated with an increase in the paired-pulse ratio. An antagonist of MORs significantly attenuated these effects. Notably, this antagonist significantly increased leEPSC amplitude when applied alone, an effect further amplified in mice subjected to lipopolysaccharide injection 2 h before brain isolation, yet not observed at the 24-h mark. We conclude that opioids could shut off the ascending nociceptive signal at the LPB-CeA synapse through presynaptic mechanisms. Moreover, this gating process might be modulated by endogenous opioids, and the innate immune system influences this modulation.

Towards a Real-Life Understanding of the Altered Functional Behaviour of the Default Mode and Salience Network in Chronic Pain: Are People with Chronic Pain Overthinking the Meaning of Their Pain?

Chronic pain is a source of substantial physical and psychological suffering, yet a clear understanding of the pathogenesis of chronic pain is lacking. Repeated studies have reported an altered behaviour of the salience network (SN) and default mode network (DMN) in people with chronic pain, and a majority of these studies report an altered behaviour of the dorsal ventromedial prefrontal cortex (vmPFC) within the anterior DMN. In this topical review, we therefore focus specifically on the role of the dorsal vmPFC in chronic pain to provide an updated perspective on the cortical mechanisms of chronic pain. We suggest that increased activity in the dorsal vmPFC may reflect maladaptive overthinking about the meaning of pain for oneself and one's actions. We also suggest that such overthinking, if negative, may increase the personal "threat" of a given context, as possibly reflected by increased activity in, and functional connectivity to, the anterior insular cortex within the SN.

Hypnosis and music interventions for anxiety, pain, sleep and well-being in palliative care: systematic review and meta-analysis

BACKGROUND

Maintaining quality of life is a primary goal of palliative care (PC). Complementary interventions can help meet the needs of patients at the end of life.

OBJECTIVES

This meta-analysis aims to (1) evaluate the feasibility, acceptability and fidelity of music and hypnosis interventions designed for patients in PC and (2) evaluate the impact of these interventions on pain, anxiety, sleep and well-being.

METHODS

Relevant studies were sourced from major databases. We selected both randomised controlled trials (RCTs) and studies relying on pre-post design with details of the intervention(s).

RESULTS

Four RCT and seven non-randomised pre-post studies met the inclusion criteria. Overall, the feasibility and acceptability of the interventions reached an adequate level of satisfaction. However, only three studies reported using a written protocol. The meta-analysis of RCT indicated a significant decrease in pain with an effect size of -0.42, p=0.003. The small number of RCT studies did not allow us to quantify the effects for other variables. Analyses of data from pre-post designs indicated a favourable outcome for pain, anxiety, sleep and well-being.

CONCLUSION

Despite the limited number of studies included in our meta-analysis, hypnosis and music intervention in the context of PC shows promising results in terms of feasibility and acceptability, as well as improvements on pain, anxiety, sleep and well-being. The available studies are insufficient to compare the efficacy across interventions and assess the potential benefits of their combinations. These results underscore the importance of further research on well-described complementary interventions relying on hypnosis and music.

PROSPERO REGISTRATION NUMBER

CRD-42021236610.

Medial Prefrontal Cortex Dysfunction Mediates Working Memory Deficits in Patients With Schizophrenia

Background

Schizophrenia (SCZ) is marked by working memory (WM) deficits, which predict poor functional outcome. While most functional magnetic resonance imaging studies of WM in SCZ have focused on the dorsolateral prefrontal cortex (PFC), some recent work suggests that the medial PFC (mPFC) may play a role. We investigated whether task-evoked mPFC deactivation is associated with WM performance and whether it mediates deficits in SCZ. In addition, we investigated associations between mPFC deactivation and cortical dopamine release.

Methods

Patients with SCZ (n = 41) and healthy control participants (HCs) (n = 40) performed a visual object n-back task during functional magnetic resonance imaging. Dopamine release capacity in mPFC was quantified with [11C]FLB457 in a subset of participants (9 SCZ, 14 HCs) using an amphetamine challenge. Correlations between task-evoked deactivation and performance were assessed in mPFC and dorsolateral PFC masks and were further examined for relationships with diagnosis and dopamine release.

Results

mPFC deactivation was associated with WM task performance, but dorsolateral PFC activation was not. Deactivation in the mPFC was reduced in patients with SCZ relative to HCs and mediated the relationship between diagnosis and WM performance. In addition, mPFC deactivation was significantly and inversely associated with dopamine release capacity across groups and in HCs alone, but not in patients.

Conclusions

Reduced WM task-evoked mPFC deactivation is a mediator of, and potential substrate for, WM impairment in SCZ, although our study design does not rule out the possibility that these findings could relate to cognition in general rather than WM specifically. We further present preliminary evidence of an inverse association between deactivation during WM tasks and dopamine release capacity in the mPFC.

Brain mediators of negative affect-induced physical symptom reporting in patients with functional somatic syndromes

Functional somatic syndromes (FSS) include fibromyalgia, irritable bowel syndrome (IBS), and others. In FSS patients, merely viewing negative affective pictures can elicit increased physical symptoms. Our aim was to investigate the neural mechanisms underlying such negative affect-induced physical symptoms in FSS patients. Thirty patients with fibromyalgia and/or IBS and 30 healthy controls (all women) watched neutral, positive and negative affective picture blocks during functional MRI scanning and rated negative affect and physical symptoms after every block. We compared brain-wide activation during negative versus neutral picture viewing in FSS patients versus controls using robust general linear model analysis. Further, we compared neurologic pain signature (NPS), stimulus intensity-independent pain signature (SIIPS) and picture-induced negative emotion signature (PINES) responses to the negative versus neutral affect contrast and investigated whether they mediated between-group differences in affective picture-induced physical symptom reporting. More physical symptoms were reported after viewing negative compared to neutral pictures, and this effect was larger in patients than controls (p = 0.025). Accordingly, patients showed stronger activation in somatosensory regions during negative versus neutral picture viewing. NPS, but not SIIPS nor PINES, responses were higher in patients than controls during negative versus neutral pictures (p = 0.026). These differential NPS responses partially mediated between-group differences in physical symptoms. In conclusion, picture-induced negative affect elicits physical symptoms in FSS patients as a result of activation of somatosensory and nociceptive brain patterns, supporting the idea that affect-driven alterations in processing of somatic signals is a critical mechanism underlying FSS.

The DNA methylation landscape of the human oxytocin receptor gene (OXTR): data-driven clusters and their relation to gene expression and childhood adversity

The oxytocin receptor gene (OXTR) is of interest when investigating the effects of early adversity on DNA methylation. However, there is heterogeneity regarding the selection of the most promising CpG sites to target for analyses. The goal of this study was to determine functionally relevant clusters of CpG sites within the OXTR CpG island in 113 mother-infant dyads, with 58 of the mothers reporting childhood maltreatment (CM). OXTR DNA methylation was analyzed in peripheral/umbilical blood mononuclear cells. Different complexity reduction approaches were used to reduce the 188 CpG sites into clusters of co-methylated sites. Furthermore, associations between OXTR DNA methylation (cluster- and site-specific level) and OXTR gene expression and CM were investigated in mothers. Results showed that, first, CpG sections differed strongly regarding their statistical utility for research of individual differences in DNA methylation. Second, cluster analyses and Partial Least Squares (PLS) suggested two clusters consisting of intron1/exon2 and the protein-coding region of exon3, respectively, as most strongly associated with outcome measures. Third, cross-validated PLS regression explained 7% of variance in CM, with low cross-validated variance explained for the prediction of gene expression. Fourth, substantial mother-child correspondence was observed in correlation patterns within the identified clusters, but only modest correspondence outside these clusters. This study makes an important contribution to the mapping of the DNA methylation landscape of the OXTR CpG island by highlighting clusters of CpG sites that show desirable statistical properties and predictive value. We provide a Companion Web Application to facilitate the choice of CpG sites.

A machine learning based approach towards high-dimensional mediation analysis

Mediation analysis is used to investigate the role of intermediate variables (mediators) that lie in the path between an exposure and an outcome variable. While significant research has focused on developing methods for assessing the influence of mediators on the exposure-outcome relationship, current approaches do not easily extend to settings where the mediator is high-dimensional. These situations are becoming increasingly common with the rapid increase of new applications measuring massive numbers of variables, including brain imaging, genomics, and metabolomics. In this work, we introduce a novel machine learning based method for identifying high dimensional mediators. The proposed algorithm iterates between using a machine learning model to map the high-dimensional mediators onto a lower-dimensional space, and using the predicted values as input in a standard three-variable mediation model. Hence, the machine learning model is trained to maximize the likelihood of the mediation model. Importantly, the proposed algorithm is agnostic to the machine learning model that is used, providing significant flexibility in the types of situations where it can be used. We illustrate the proposed methodology using data from two functional Magnetic Resonance Imaging (fMRI) studies. First, using data from a task-based fMRI study of thermal pain, we combine the proposed algorithm with a deep learning model to detect distributed, network-level brain patterns mediating the relationship between stimulus intensity (temperature) and reported pain at the single trial level. Second, using resting-state fMRI data from the Human Connectome Project, we combine the proposed algorithm with a connectome-based predictive modeling approach to determine brain functional connectivity measures that mediate the relationship between fluid intelligence and working memory accuracy. In both cases, our multivariate mediation model links exposure variables (thermal pain or fluid intelligence), high dimensional brain measures (single-trial brain activation maps or resting-state brain connectivity) and behavioral outcomes (pain report or working memory accuracy) into a single unified model. Using the proposed approach, we are able to identify brain-based measures that simultaneously encode the exposure variable and correlate with the behavioral outcome.

Associations between neighborhood socioeconomic status, parental education, and executive system activation in youth

Socioeconomic status (SES) can impact cognitive performance, including working memory (WM). As executive systems that support WM undergo functional neurodevelopment during adolescence, environmental stressors at both individual and community levels may influence cognitive outcomes. Here, we sought to examine how SES at the neighborhood and family level impacts task-related activation of the executive system during adolescence and determine whether this effect mediates the relationship between SES and WM performance. To address these questions, we studied 1,150 youths (age 8-23) that completed a fractal n-back WM task during functional magnetic resonance imaging at 3T as part of the Philadelphia Neurodevelopmental Cohort. We found that both higher neighborhood SES and parental education were associated with greater activation of the executive system to WM load, including the bilateral dorsolateral prefrontal cortex, posterior parietal cortex, and precuneus. The association of neighborhood SES remained significant when controlling for task performance, or related factors like exposure to traumatic events. Furthermore, high-dimensional multivariate mediation analysis identified distinct patterns of brain activity within the executive system that significantly mediated the relationship between measures of SES and task performance. These findings underscore the importance of multilevel environmental factors in shaping executive system function and WM in youth.

Pain control based on oscillatory brain activity using transcranial alternating current stimulation: An integrative review

Developing effective tools and strategies to relieve chronic pain is a high-priority scientific and clinical goal. In particular, the brain regions related to pain processing have been investigated as potential targets to relieve pain by non-invasive brain stimulation (NIBS). In addition to elucidating the relationship between pain and oscillatory brain activity, transcranial alternating current stimulation (tACS), which can non-invasively entrain oscillatory brain activity and modulate oscillatory brain communication, has attracted scientific attention as a possible technique to control pain. This review focuses on the use of tACS to relieve pain through the manipulation of oscillatory brain activity and its potential clinical applications. Several studies have reported that tACS on a single brain reduces pain by normalizing abnormal oscillatory brain activity in patients with chronic pain. Interpersonal tACS approaches based on inter-brain synchrony to manipulate inter-brain communication may result in pain relief via prosocial effects. Pain is encoded by the spatiotemporal neural communication that represents the integration of cognitive, emotional-affective, and sensorimotor aspects of pain. Therefore, future studies should seek to identify the pathological oscillatory brain communication in chronic pain as a therapeutic target for tACS. In conclusion, tACS could be effective for re-establishing oscillatory brain activity and assisting social interaction, and it might help develop novel approaches for pain control.

The Role of the Skin in Interoception: A Neglected Organ?

In the past 2 decades, interoception has received increasing attention in the fields of psychology and cognitive science, as well as neuroscience and physiology. A plethora of studies adopted the perception of cardiac signals as a proxy for interoception. However, recent findings have cast doubt on the methodological and intrinsic validity of the tasks used thus far. Therefore, there is an ongoing effort to improve the existing cardiac interoceptive tasks and to identify novel channels to target the perception of the physiological state of the body. Amid such scientific abundancy, one could question whether the field has been partially neglecting one of our widest organs in terms of dimensions and functions: the skin. According to some views grounded on anatomical and physiological evidence, skin-mediated signals such as affective touch, pain, and temperature have been redefined as interoceptive. However, there is no agreement in this regard. Here, we discuss some of the anatomical, physiological, and experimental arguments supporting the scientific study of interoception by means of skin-mediated signals. We argue that more attention should be paid to the skin as a sensory organ that monitors the bodily physiological state and further propose thermosensation as a particularly attractive model of skin-mediated interoception.

Migraine disability, pain catastrophizing, and headache severity are associated with evoked pain and targeted by mind-body therapy

ABSTRACT

Meta-analysis suggests that migraine patients are no more sensitive to experimentally evoked pain than healthy control subjects. At the same time, studies have linked some migraine symptoms to quantitative sensory testing (QST) profiles. Unfortunately, previous studies associating migraine symptoms and QST have important methodological shortcomings, stemming from small sample sizes, and frequent use of univariate statistics for multivariate research questions. In the current study, we seek to address these limitations by using a large sample of episodic migraine patients (n = 103) and a multivariate analysis that associates pain ratings from many thermal intensities simultaneously with 12 clinical measures ranging from headache frequency to sleep abnormalities. We identified a single dimension of association between thermal QST and migraine symptoms that relates to pain ratings for all stimulus intensities and a subset of migraine symptoms relating to disability (Headache Impact Test 6 and Brief Pain Inventory interference), catastrophizing (Pain Catastrophizing Scale), and pain severity (average headache pain, Brief Pain Inventory severity, and Short-Form McGill Pain Questionnaire 2). Headache frequency, allodynia, affect, and sleep disturbances were unrelated to this dimension. Consistent with previous research, we did not observe any difference in QST ratings between migraine patients and healthy control subjects. Additionally, we found that the linear combination of symptoms related to QST was modified by the mind-body therapy enhanced mindfulness-based stress reduction (MBSR+). These results suggest that QST has a selective relationship with pain symptoms even in the absence of between-subjects differences between chronic pain patients and healthy control subjects.

Multiple spatial scale mapping of time-resolved brain network reconfiguration during evoked pain in patients with rheumatoid arthritis

Functional brain networks and the perception of pain can fluctuate over time. However, how the time-dependent reconfiguration of functional brain networks contributes to chronic pain remains largely unexplained. Here, we explored time-varying changes in brain network integration and segregation during pain over a disease-affected area (joint) compared to a neutral site (thumbnail) in 28 patients with rheumatoid arthritis (RA) in comparison with 22 healthy controls (HC). During functional magnetic resonance imaging, all subjects received individually calibrated pain pressures corresponding to visual analog scale 50 mm at joint and thumbnail. We implemented a novel approach to track changes of task-based network connectivity over time. Within this framework, we quantified measures of integration (participation coefficient, PC) and segregation (within-module degree z-score). Using these network measures at multiple spatial scales, both at the level of single nodes (brain regions) and communities (clusters of nodes), we found that PC at the community level was generally higher in RA patients compared to HC during and after painful pressure over the inflamed joint and corresponding site in HC. This shows that all brain communities integrate more in RA patients than in HC for time points following painful stimulation to a disease-relevant body site. However, the elevated community-related integration seen in patients appeared to not pertain uniquely to painful stimulation at the inflamed joint, but also at the neutral thumbnail, as integration and segregation at the community level did not differ across body sites in patients. Moreover, there was no specific nodal contribution to brain network integration or segregation. Altogether, our findings indicate widespread and persistent changes in network interaction in RA patients compared to HC in response to painful stimulation.

Comorbid depressive symptoms can aggravate the functional changes of the pain matrix in patients with chronic back pain: A resting-state fMRI study

Objective

The purposes of this study are to explore (1) whether comorbid depressive symptoms in patients with chronic back pain (CBP) affect the pain matrix. And (2) whether the interaction of depression and CBP exacerbates impaired brain function.

Methods

Thirty-two patients with CBP without comorbid depressive symptoms and thirty patients with CBP with comorbid depressive symptoms were recruited. All subjects underwent functional magnetic resonance imaging (fMRI) scans. The graph theory analysis, mediation analysis, and functional connectivity (FC) analysis were included in this study. All subjects received the detection of clinical depressive symptoms and pain-related manifestations.

Result

Compared with the CBP group, subjects in the CBP with comorbid depressive symptoms (CBP-D) group had significantly increased FC in the left medial prefrontal cortex and several parietal cortical regions. The results of the graph theory analyses showed that the area under the curve of small-world property (t = −2.175, p = 0.034), gamma (t = −2.332, p = 0.023), and local efficiency (t = −2.461, p = 0.017) in the CBP-D group were significantly lower. The nodal efficiency in the ventral posterior insula (VPI) (t = −3.581, p = 0.0007), and the network efficiency values (t = −2.758, p = 0.008) in the pain matrix were significantly lower in the CBP-D group. Both the topological properties and the FC values of these brain regions were significantly correlated with self-rating depression scale (SDS) scores (all FDR corrected) but not with pain intensity. Further mediation analyses demonstrated that pain intensity had a mediating effect on the relationship between SDS scores and Pain Disability Index scores. Likewise, the SDS scores mediated the relationship between pain intensity and PDI scores.

Conclusion

Our study found that comorbid depressive symptoms can aggravate the impairment of pain matrix function of CBP, but this impairment cannot directly lead to the increase of pain intensity, which may be because some brain regions of the pain matrix are the common neural basis of depression and CBP.

Anxiety-Related Frontocortical Activity Is Associated With Dampened Stressor Reactivity in the Real World

Negative affect is a fundamental dimension of human emotion. When extreme, it contributes to a variety of adverse outcomes, from physical and mental illness to divorce and premature death. Mechanistic work in animals and neuroimaging research in humans and monkeys have begun to reveal the broad contours of the neural circuits governing negative affect, but the relevance of these discoveries to everyday distress remains incompletely understood. Here, we used a combination of approaches-including neuroimaging assays of threat anticipation and emotional-face perception and more than 10,000 momentary assessments of emotional experience-to demonstrate that individuals who showed greater activation in a cingulo-opercular circuit during an anxiety-eliciting laboratory paradigm experienced lower levels of stressor-dependent distress in their daily lives (ns = 202-208 university students). Extended amygdala activation was not significantly related to momentary negative affect. These observations provide a framework for understanding the neurobiology of negative affect in the laboratory and in the real world.

Intensity-dependent modulation of cortical somatosensory processing during external, low-frequency peripheral nerve stimulation in humans

External low-frequency peripheral nerve stimulation (LFS) has been proposed as a novel method for neuropathic pain relief. Previous studies have reported that LFS elicits long-term depression-like effects on human pain perception when delivered at noxious intensities, whereas lower intensities are ineffective. To shed light on cortical regions mediating the effects of LFS, we investigated changes in somatosensory-evoked potentials (SEPs) during four LFS intensities. LFS was applied to the radial nerve (600 pulses, 1 Hz) of 24 healthy participants at perception (1 times), low (5 times), medium (10 times), and high intensities (15 times detection threshold). SEPs were recorded during LFS, and averaged SEPs in 10 consecutive 1-min epochs of LFS were analyzed using source dipole modeling. Changes in resting electroencephalography (EEG) were investigated after each LFS block. Source activity in the midcingulate cortex (MCC) decreased linearly during LFS, with greater attenuation at stronger LFS intensities, and in the ipsilateral operculo-insular cortex during the two lowest LFS stimulus intensities. Increased LFS intensities resulted in greater augmentation of contralateral primary sensorimotor cortex (SI/MI) activity. Stronger LFS intensities were followed by increased α (alpha, 9-11 Hz) band power in SI/MI and decreased θ (theta, 3-5 Hz) band power in MCC. Intensity-dependent attenuation of MCC activity with LFS is consistent with a state of long-term depression. Sustained increases in contralateral SI/MI activity suggests that effects of LFS on somatosensory processing may also be dependent on satiation of SI/MI. Further research could clarify if the activation of SI/MI during LFS competes with nociceptive processing in neuropathic pain.NEW & NOTEWORTHY Somatosensory-evoked potentials during low-frequency stimulation of peripheral nerves were examined at graded stimulus intensities. Low-frequency stimulation was associated with decreased responsiveness in the midcingulate cortex and increased responsiveness in primary sensorimotor cortex. Greater intensities were associated with increased midcingulate cortex θ band power and decreased sensorimotor cortex α band power. Results further previous evidence of an inhibition of somatosensory processing during and after low-frequency stimulation and point toward a potential augmentation of activity in somatosensory processing regions.

Limits of decoding mental states with fMRI

A growing number of studies claim to decode mental states using multi-voxel decoders of brain activity. It has been proposed that the fixed, fine-grained, multi-voxel patterns in these decoders are necessary for discriminating between and identifying mental states. Here, we present evidence that the efficacy of these decoders might be overstated. Across various tasks, decoder patterns were spatially imprecise, as decoder performance was unaffected by spatial smoothing; 90% redundant, as selecting a random 10% of a decoder's constituent voxels recovered full decoder performance; and performed similarly to brain activity maps used as decoders. We distinguish decoder performance in discriminating between mental states from performance in identifying a given mental state, and show that even when discrimination performance is adequate, identification can be poor. Finally, we demonstrate that simple and intuitive similarity metrics explain 91% and 62% of discrimination performance within- and across-subjects, respectively. These findings indicate that currently used across-subject decoders of mental states are superfluous and inappropriate for decision-making.

Supraspinal Mechanisms Underlying Ocular Pain

Supraspinal mechanisms of pain are increasingly understood to underlie neuropathic ocular conditions previously thought to be exclusively peripheral in nature. Isolating individual causes of centralized chronic conditions and differentiating them is critical to understanding the mechanisms underlying neuropathic eye pain and ultimately its treatment. Though few functional imaging studies have focused on the eye as an end-organ for the transduction of noxious stimuli, the brain networks related to pain processing have been extensively studied with functional neuroimaging over the past 20 years. This article will review the supraspinal mechanisms that underlie pain as they relate to the eye.

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.

Brain Network Segregation and Integration during Painful Thermal Stimulation

The present study aimed to determine changes in brain network integration/segregation during thermal pain using methods optimized for network connectivity events with high temporal resolution. Participants (n = 33) actively judged whether thermal stimuli applied to the volar forearm were painful or not and then rated the warmth/pain intensity after each trial. We show that the temporal evolution of integration/segregation within trials correlates with the subjective ratings of pain. Specifically, the brain shifts from a segregated state to an integrated state when processing painful stimuli. The association with subjective pain ratings occurred at different time points for all networks. However, the degree of association between ratings and integration/segregation vanished for several brain networks when time-varying functional connectivity was measured at lower temporal resolution. Moreover, the increased integration associated with pain is explained to some degree by relative increases in between-network connectivity. Our results highlight the importance of investigating the relationship between pain and brain network connectivity at a single time point scale, since commonly used temporal aggregations of connectivity data may result in that fine-scale changes in network connectivity may go unnoticed. The interplay between integration/segregation reflects shifting demands of information processing between brain networks and this adaptation occurs both for cognitive tasks and nociceptive processing.

The Brain Activation-Based Sexual Image Classifier (BASIC): A Sensitive and Specific fMRI Activity Pattern for Sexual Image Processing

Previous studies suggest there is a complex relationship between sexual and general affective stimulus processing, which varies across individuals and situations. We examined whether sexual and general affective processing can be distinguished at the brain level. In addition, we explored to what degree possible distinctions are generalizable across individuals and different types of sexual stimuli, and whether they are limited to the engagement of lower-level processes, such as the detection of visual features. Data on sexual images, nonsexual positive and negative images, and neutral images from Wehrum et al. (2013) (N = 100) were reanalyzed using multivariate support vector machine models to create the brain activation-based sexual image classifier (BASIC) model. This model was tested for sensitivity, specificity, and generalizability in cross-validation (N = 100) and an independent test cohort (N = 18; Kragel et al. 2019). The BASIC model showed highly accurate performance (94–100%) in classifying sexual versus neutral or nonsexual affective images in both datasets with forced choice tests. Virtual lesions and tests of individual large-scale networks (e.g., visual or attention networks) show that individual networks are neither necessary nor sufficient to classify sexual versus nonsexual stimulus processing. Thus, responses to sexual images are distributed across brain systems.

Low Somatosensory Cortex Excitability in the Acute Stage of Low Back Pain Causes Chronic Pain

Determining the mechanistic causes of complex biopsychosocial health conditions such as low back pain (LBP) is challenging, and research is scarce. Cross-sectional studies demonstrate altered excitability and organization of the somatosensory and motor cortex in people with acute and chronic LBP, however, no study has explored these mechanisms longitudinally or attempted to draw causal inferences. Using sensory evoked potential area measurements and transcranial magnetic stimulation derived map volume we analyzed somatosensory and motor cortex excitability in 120 adults experiencing acute LBP. Following multivariable regression modelling with adjustment for confounding, we identified lower primary (OR = 2.08, 95% CI = 1.22-3.57) and secondary (OR = 2.56, 95% CI = 1.37-4.76) somatosensory cortex excitability significantly increased the odds of developing chronic pain at 6-month follow-up. Corticomotor excitability in the acute stage of LBP was associated with higher pain intensity at 6-month follow-up (B = -0.15, 95% CI: -0.28 to -0.02) but this association did not remain after confounder adjustment. These data provide evidence that low somatosensory cortex excitability in the acute stage of LBP is a cause of chronic pain. PERSPECTIVE: This prospective longitudinal cohort study design identified low sensorimotor cortex excitability during the acute stage of LBP in people who developed chronic pain. Interventions that target this proposed mechanism may be relevant to the prevention of chronic pain.

Getting in touch: A neural model of comforting touch

Comforting touch involves contact distress-alleviating behaviors of an observer towards the suffering of a target. A growing number of studies have investigated the effects of touch on pain attenuation, focusing on the (toucher), the target (comforted) or both. Here we synthesize findings of brain mechanisms underlying comforting touch in the target and toucher to propose an integrative brain model for understanding how touch attenuates distress. Building on evidence from the pain and distress literatures, our model applies interchangeably to pain and distress regulation. We describe comforting touch as a feedback-loop that begins with distress experienced by the target, triggering an empathic response in the toucher which in turn reduces distress in the target. This cycle is mediated by interactions between the neural circuits associated with touch perception, shared distress, emotion regulation and reward as well as brain-to-brain coupling in the observation-execution system. We conclude that formulating a model of comforting touch offers a mechanistic framework for understanding the effects of touch as well as other social interactions involving social support.

Active role of the central amygdala in widespread mechanical sensitization in rats with facial inflammatory pain

ABSTRACT

Widespread or ectopic sensitization is a hallmark symptom of chronic pain, characterized by aberrantly enhanced pain sensitivity in multiple body regions remote from the site of original injury or inflammation. The central mechanism underlying widespread sensitization remains unidentified. The central nucleus of the amygdala (also called the central amygdala, CeA) is well situated for this role because it receives nociceptive information from diverse body sites and modulates pain sensitivity in various body regions. In this study, we examined the role of the CeA in a novel model of ectopic sensitization of rats. Injection of formalin into the left upper lip resulted in latent bilateral sensitization in the hind paw lasting >13 days in male Wistar rats. Chemogenetic inhibition of gamma-aminobutyric acid-ergic neurons or blockade of calcitonin gene-related peptide receptors in the right CeA, but not in the left, significantly attenuated this sensitization. Furthermore, chemogenetic excitation of gamma-aminobutyric acid-ergic neurons in the right CeA induced de novo bilateral hind paw sensitization in the rats without inflammation. These results indicate that the CeA neuronal activity determines hind paw tactile sensitivity in rats with remote inflammatory pain. They also suggest that the hind paw sensitization used in a large number of preclinical studies might not be simply a sign of the pain at the site of injury but rather a representation of the augmented CeA activity resulting from inflammation/pain in any part of the body or from activities of other brain regions, which has an active role of promoting defensive/protective behaviors to avoid further bodily damage.

Genetic Influence on Nociceptive Processing in the Human Brain-A Twin Study

Nociceptive processing in the human brain is complex and involves several brain structures and varies across individuals. Determining the structures that contribute to interindividual differences in nociceptive processing is likely to improve our understanding of why some individuals feel more pain than others. Here, we found specific parts of the cerebral response to nociception that are under genetic influence by employing a classic twin-design. We found genetic influences on nociceptive processing in the midcingulate cortex and bilateral posterior insula. In addition to brain activations, we found genetic contributions to large-scale functional connectivity (FC) during nociceptive processing. We conclude that additive genetics influence specific brain regions involved in nociceptive processing. The genetic influence on FC during nociceptive processing is not limited to core nociceptive brain regions, such as the dorsal posterior insula and somatosensory areas, but also involves cognitive and affective brain circuitry. These findings improve our understanding of human pain perception and increases chances to find new treatments for clinical pain.

Inhibition of cortical somatosensory processing during and after low frequency peripheral nerve stimulation in humans

OBJECTIVE

Transcutaneous low-frequency stimulation (LFS) elicits long-term depression-like effects on human pain perception. However, the neural mechanisms underlying LFS are poorly understood. We investigated cortical activation changes occurring during LFS and if changes were associated with reduced nociceptive processing and increased amplitude of spontaneous cortical oscillations post-treatment.

METHODS

LFS was applied to the radial nerve of 25 healthy volunteers over two sessions using active (1 Hz) or sham (0.02 Hz) frequencies. Changes in resting electroencephalography (EEG) and laser-evoked potentials (LEPs) were investigated before and after LFS. Somatosensory-evoked potentials were recorded during LFS and source analysis was carried out.

RESULTS

Ipsilateral midcingulate and operculo-insular cortex source activity declined linearly during LFS. Active LFS was associated with attenuated long-latency LEP amplitude in ipsilateral frontocentral electrodes and increased resting alpha (8-12 Hz) and beta (16-24 Hz) band power in electrodes overlying operculo-insular, sensorimotor and frontal cortical regions. Reduced ipsilateral operculo-insular cortex source activity during LFS correlated with a smaller post-treatment alpha-band power increase.

CONCLUSIONS

LFS attenuated somatosensory processing both during and after stimulation.

SIGNIFICANCE

Results further our understanding of the attenuation of somatosensory processing both during and after LFS.

Neuropathic corneal pain and dry eye: a continuum of nociception

Throughout the body, damage to peripheral nerves normally involved in nociception may produce a constellation of symptoms-including irritation, itchiness and pain. The neurobiological processes involved in corneal symptoms of dry eye (DE) and neuropathic corneal pain (NCP) have not been clearly considered in terms of nociceptive processing. The conventional underlying presumption is that a labelled line principle is responsible; that these distinct perceptions are hard coded by primary afferent inputs to the central nervous system. This presumption oversimplifies the neurobiological mechanisms underlying somatosensory perception. The labelled line perspective that DE represents a chronic pain condition does not make intuitive sense: how can an eye condition that is not painful in most cases be considered a pain condition? Does not chronic pain by definition require pain to be present? On the other hand, NCP, a term that clearly denotes a painful condition, has historically seemed to resonate with clinical significance. Both DE and NCP can share similar features, yet their differentiation is not always clear. As is often the case, clinical terms arise from different disciplines, with DE evolving from ophthalmological findings and NCP inspired by pain neurophysiology. This review evaluates the current definition of these terms, the rationale for their overlap and how the neurophysiology of itch impacts our understanding of these conditions as a continuum of the same disease. Despite the complexity of nociceptive physiology, an understanding of these mechanisms will allow us a more precise therapeutic approach.

Identifying neural signatures mediating behavioral symptoms and psychosis onset: High-dimensional whole brain functional mediation analysis

Along the pathway from behavioral symptoms to the development of psychotic disorders sits the multivariate mediating brain. The functional organization and structural topography of large-scale multivariate neural mediators among patients with brain disorders, however, are not well understood. Here, we design a high-dimensional brain-wide functional mediation framework to investigate brain regions that intermediate between baseline behavioral symptoms and future conversion to full psychosis among individuals at clinical high risk (CHR). Using resting-state functional magnetic resonance imaging (fMRI) data from 263 CHR subjects, we extract an α brain atlas and a β brain atlas: the former underlines brain areas associated with prodromal symptoms and the latter highlights brain areas associated with disease onset. In parallel, we identify and separate mediators that potentially positively and negatively mediate symptoms and psychosis, respectively, and quantify the effect of each neural mediator on disease development. Taken together, these results paint a brain-wide picture of neural markers that are potentially mediating behavioral symptoms and the development of psychotic disorders; additionally, they underscore a statistical framework that is useful to uncover large-scale intermediating variables in a regulatory biological system.

A nociresponsive specific area of human somatosensory cortex within BA3a: BA3c?

It is well recognized that in primates, including humans, noxious body stimulation evokes a neural response in the posterior bank of the central sulcus, in Brodmann cytoarchitectonic subdivisions 3b and 1 of the primary somatosensory cortex. This response is associated with the 1st/sharp pain and contributes to sensory discriminative aspects of pain perception and spatial localization of the noxious stimulus. However, neurophysiological studies in New World monkeys predict that in humans noxious stimulation also evokes a separate neural response-mediated by C-afferent drive and associated with the 2nd/burning pain-in the depth of the central sulcus in Brodmann area 3a (BA3a) at the transition between the somatosensory and motor cortices. To evoke such a response, it is necessary to use multi-second duration noxious stimulation, rather than brief laser pulses. Given the limited human pain-imaging literature on cortical responses induced by C-nociceptive input specifically within BA3a, here we used high spatial resolution 7T fMRI to study the response to thermonoxious skin stimulation. We observed the predicted response of BA3a in the depth of the central sulcus in five human volunteers. Review of the available evidence suggests that the nociresponsive region in the depth of the central sulcus is a structurally and functionally distinct cortical area that should not be confused with proprioceptive BA3a. It is most likely engaged in interoception and control of the autonomic nervous system, and contributes to the sympathetic response to noxious stimulation, arguably the most intolerable aspect of pain experience. Ablation of this region has been shown to reduce pain sensibility and might offer an effective means of ameliorating some pathological pain conditions.

Sparse Principal Component based High-Dimensional Mediation Analysis

Causal mediation analysis aims to quantify the intermediate effect of a mediator on the causal pathway from treatment to outcome. When dealing with multiple mediators, which are potentially causally dependent, the possible decomposition of pathway effects grows exponentially with the number of mediators. An existing approach incorporated the principal component analysis (PCA) to address this challenge based on the fact that the transformed mediators are conditionally independent given the orthogonality of the principal components (PCs). However, the transformed mediator PCs, which are linear combinations of original mediators, can be difficult to interpret. A sparse high-dimensional mediation analysis approach is proposed which adopts the sparse PCA method to the mediation setting. The proposed approach is applied to a task-based functional magnetic resonance imaging study, illustrating its ability to detect biologically meaningful results related to an identified mediator.