Subcortical structures involved in pain processing: evidence from single-trial fMRI

Advances in the fMRI analysis of the default mode network: a review

The default mode network (DMN) is a singular pattern of synchronization between brain regions, usually observed using resting-state functional magnetic resonance imaging (rs-fMRI) and functional connectivity analyses. In comparison to other brain networks that are primarily involved in attentional-demanding tasks (such as the frontoparietal network), the DMN is linked with self-referential activities, and alterations in its pattern of connectivity have been related to a wide range of disorders. Structural connectivity analyses have highlighted the vital role of the posterior cingulate cortex and the precuneus as integrative hubs, and advanced parcellation methods have further contributed to elucidate the DMN's regions, enriching its explanatory potential across cognitive functions and dysfunctions. Interestingly, the study of its temporal characteristics - the specific frequency spectrum of BOLD signal oscillations -, its developmental trajectory over the course of life, and its interaction with other networks, provides new insight into the DMN's defining features. In this context, this review aims to synthesize the state of the art in the study of the DMN to provide the most updated findings to anyone interested in its research. Finally, some weaknesses in the current state of knowledge and some interesting lines of work for further progress in the study of the DMN are presented.

Peripheral and central pathogenesis of postherpetic neuralgia

BACKGROUND

Postherpetic neuralgia (PHN) is a classic chronic condition with multiple signs of peripheral and central neuropathy. Unfortunately, the pathogenesis of PHN is not well defined, limiting clinical treatment and disease management.

OBJECTIVE

To describe the peripheral and central pathological axes of PHN, including peripheral nerve injury, inflammation induction, central nervous system sensitization, and brain functional and structural network activity.

METHODS

A bibliographic survey was carried out, selecting relevant articles that evaluated the characterization of the pathogenesis of PHN, including peripheral and central pathological axes.

RESULTS

Currently, due to the complexity of the pathophysiological mechanisms of PHN and the incomplete understanding of the exact mechanism of neuralgia.

CONCLUSION

It is essential to conduct in-depth research to clarify the origins of PHN pathogenesis and explore effective and comprehensive therapies for PHN.

Altered static and dynamic functional brain network in knee osteoarthritis: A resting-state functional magnetic resonance imaging study: Static and dynamic FNC in KOA

This study aimed to investigate altered static and dynamic functional network connectivity (FNC) and its correlation with clinical symptoms in patients with knee osteoarthritis (KOA). One hundred and fifty-nine patients with KOA and 73 age- and gender-matched healthy subjects (HS) underwent resting-state functional magnetic resonance imaging (rs-fMRI) and clinical evaluations. Group independent component analysis (GICA) was applied, and seven resting-state networks were identified. Patients with KOA had decreased static FNC within the default mode network (DM), visual network (VS), and cerebellar network (CB) and increased static FNC between the subcortical network (SC) and VS (p < 0.05, FDR corrected). Four reoccurring FNC states were identified using k-means clustering analysis. Although abnormalities in dynamic FNCs of KOA patients have been found using the common window size (22 TR, 44 s), but the results of the clustering analysis were inconsistent when using different window sizes, suggesting dynamic FNCs might be an unstable method to compare brain function between KOA patients and HS. These recent findings illustrate that patients with KOA have a wide range of abnormalities in the static and dynamic FNCs, which provided a reference for the identification of potential central nervous therapeutic targets for KOA treatment and might shed light on the other musculoskeletal pain neuroimaging studies.

Does pain hurt more in Spanish? The neurobiology of pain among Spanish-English bilingual adults

We previously found Spanish-English bilingual adults reported higher pain intensity when exposed to painful heat in the language of their stronger cultural orientation. Here, we elucidate brain systems involved in language-driven alterations in pain responses. During separate English- and Spanish-speaking fMRI scanning runs, 39 (21 female) bilingual adults rated painful heat intermixed between culturally evocative images and completed sentence reading tasks. Surveys of cultural identity and language use measured relative preference for US-American vs Hispanic culture (cultural orientation). Participants produced higher intensity ratings in Spanish compared to English. Group-level whole-brain differences in pain-evoked activity between languages emerged in somatosensory, cingulate, precuneus and cerebellar cortex. Regions of interest associated with semantic, attention and somatosensory processing showed higher average pain-evoked responses in participants' culturally preferred language, as did expression of a multivariate pain-predictive pattern. Follow-up moderated mediation analyses showed somatosensory activity mediated language effects on pain intensity, particularly for Hispanic oriented participants. These findings relate to distinct ('meddler', 'spotlight' and 'inducer') hypotheses about the nature of language effects on perception and cognition. Knowledge of language influences on pain could improve efficacy of culturally sensitive treatment approaches across the diversity of Hispanic adults to mitigate documented health disparities in this population.

Brain morphology predicts individual sensitivity to pain: a multicenter machine learning approach

ABSTRACT

Sensitivity to pain shows a remarkable interindividual variance that has been reported to both forecast and accompany various clinical pain conditions. Although pain thresholds have been reported to be associated to brain morphology, it is still unclear how well these findings replicate in independent data and whether they are powerful enough to provide reliable pain sensitivity predictions on the individual level. In this study, we constructed a predictive model of pain sensitivity (as measured with pain thresholds) using structural magnetic resonance imaging-based cortical thickness data from a multicentre data set (3 centres and 131 healthy participants). Cross-validated estimates revealed a statistically significant and clinically relevant predictive performance (Pearson r = 0.36, P < 0.0002, R2 = 0.13). The predictions were found to be specific to physical pain thresholds and not biased towards potential confounding effects (eg, anxiety, stress, depression, centre effects, and pain self-evaluation). Analysis of model coefficients suggests that the most robust cortical thickness predictors of pain sensitivity are the right rostral anterior cingulate gyrus, left parahippocampal gyrus, and left temporal pole. Cortical thickness in these regions was negatively correlated to pain sensitivity. Our results can be considered as a proof-of-concept for the capacity of brain morphology to predict pain sensitivity, paving the way towards future multimodal brain-based biomarkers of pain.

Perspectives on pain in Down syndrome

Down syndrome (DS) or trisomy 21 is a genetic condition often accompanied by chronic pain caused by congenital abnormalities and/or conditions, such as osteoarthritis, recurrent infections, and leukemia. Although DS patients are more susceptible to chronic pain as compared to the general population, the pain experience in these individuals may vary, attributed to the heterogenous structural and functional differences in the central nervous system, which might result in abnormal pain sensory information transduction, transmission, modulation, and perception. We tried to elaborate on some key questions and possible explanations in this review. Further clarification of the mechanisms underlying such abnormal conditions induced by the structural and functional differences is needed to help pain management in DS patients.

Resting state functional connectivity differentiation of neuropathic and nociceptive pain in individuals with chronic spinal cord injury

Many individuals with spinal cord injury live with debilitating chronic pain that may be neuropathic, nociceptive, or a combination of both in nature. Identification of brain regions demonstrating altered connectivity associated with the type and severity of pain experience may elucidate underlying mechanisms, as well as treatment targets. Resting state and sensorimotor task-based magnetic resonance imaging data were collected in 37 individuals with chronic spinal cord injury. Seed-based correlations were utilized to identify resting state functional connectivity of regions with established roles in pain processing: the primary motor and somatosensory cortices, cingulate, insula, hippocampus, parahippocampal gyri, thalamus, amygdala, caudate, putamen, and periaqueductal gray matter. Resting state functional connectivity alterations and task-based activation associated with individuals' pain type and intensity ratings on the International Spinal Cord Injury Basic Pain Dataset (0-10 scale) were evaluated. We found that intralimbic and limbostriatal resting state connectivity alterations are uniquely associated with neuropathic pain severity, whereas thalamocortical and thalamolimbic connectivity alterations are associated specifically with nociceptive pain severity. The joint effect and contrast of both pain types were associated with altered limbocortical connectivity. No significant differences in task-based activation were identified. These findings suggest that the experience of pain in individuals with spinal cord injury may be associated with unique alterations in resting state functional connectivity dependent upon pain type.

Progress in the mechanism of acupuncture intervention on pain emotion and pain cognition mediated by limbic system

Pain is a complex physiological and psychological activity, involving at least three dimensions, including pain sensation, pain emotion, and pain cognition. Acupuncture can clearly relieve the pain sensation of patients and improve pain emotion and pain cognition induced by pain; acupuncture participates in the multi-dimensional regulation of pain through brain regions of the limbic system such as anterior cingulate cortex (ACC), amygdala (AMY), and hippocampus. By analyzing relevant literature, it has been found that the regulation of acupuncture on pain emotion is mainly related to the activation of pertinent opioid receptors in the ACC, the decrease of the expression of extracellular signal-regulated kinase (ERK), and the promotion of the expression of glutamic acid (Glu) A1, metabotropic glutamate receptor-1 (mGluR1), and γ-aminobutyric acid aminobutyric acid (GABA) B2 protein in the AMY. The regulation of acupuncture on pain cognition is mainly related to the elevation of the expression of protein kinase A (PKA) and phospho-p38 mitogen-activated protein kinase (phospho-p38 MAPK) and the inhibition of cyclic adenosine monophosphate (cAMP)/PKA/cAMP response element-binding protein (CREB) signaling pathway in the ACC.

Distinct neural networks derived from galanin-containing nociceptors and neurotensin-expressing pruriceptors

Pain and itch are distinct sensations arousing evasion and compulsive desire for scratching, respectively. It's unclear whether they could invoke different neural networks in the brain. Here, we use the type 1 herpes simplex virus H129 strain to trace the neural networks derived from two types of dorsal root ganglia (DRG) neurons: one kind of polymodal nociceptors containing galanin (Gal) and one type of pruriceptors expressing neurotensin (Nts). The DRG microinjection and immunosuppression were performed in transgenic mice to achieve a successful tracing from specific types of DRG neurons to the primary sensory cortex. About one-third of nuclei in the brain were labeled. More than half of them were differentially labeled in two networks. For the ascending pathways, the spinothalamic tract was absent in the network derived from Nts-expressing pruriceptors, and the two networks shared the spinobulbar projections but occupied different subnuclei. As to the motor systems, more neurons in the primary motor cortex and red nucleus of the somatic motor system participated in the Gal-containing nociceptor-derived network, while more neurons in the nucleus of the solitary tract (NST) and the dorsal motor nucleus of vagus nerve (DMX) of the emotional motor system was found in the Nts-expressing pruriceptor-derived network. Functional validation of differentially labeled nuclei by c-Fos test and chemogenetic inhibition suggested the red nucleus in facilitating the response to noxious heat and the NST/DMX in regulating the histamine-induced scratching. Thus, we reveal the organization of neural networks in a DRG neuron type-dependent manner for processing pain and itch.

Neuroanatomical predictors of complex skill acquisition during video game training

It is known that the outcomes of complex video game (VG) skill acquisition are correlated with individual differences in demographic and behavioral variables, such as age, intelligence and visual attention. However, empirical studies of the relationship between neuroanatomical features and success in VG training have been few and far between. The present review summarizes existing literature on gray matter (GM) and white matter correlates of complex VG skill acquisition as well as explores its relationship with neuroplasticity. In particular, since age can be an important factor in the acquisition of new cognitive skills, we present studies that compare different age groups (young and old adults). Our review reveals that GM in subcortical brain areas predicts complex VG learning outcomes in young subjects, whereas in older subjects the same is true of cortical frontal areas. This may be linked to age-related compensatory mechanisms in the frontal areas, as proposed by The Scaffolding Theory of Aging and Cognition. In the case of plasticity, there is no such relationship - in the group of younger and older adults there are changes after training in both cortical and subcortical areas. We also summarize best practices in research on predictors of VG training performance and outline promising areas of research in the study of complex video game skill acquisition.

Increased functional connectivity between limbic brain areas in healthy individuals with high versus low sensitivity to cold pain: A resting state fMRI study

BACKGROUND

The representation of variability in sensitivity to pain by differences in neural connectivity patterns and its association with psychological factors needs further investigation. This study assessed differences in resting-state functional connectivity (rsFC) and its association to cognitive-affective aspects of pain in two groups of healthy subjects with low versus high sensitivity to pain (LSP vs. HSP). We hypothesized that HSP will show stronger connectivity in brain regions involved in the affective-motivational processing of pain and that this higher connectivity would be related to negative affective and cognitive evaluations of pain.

METHODS

Forty-eight healthy subjects were allocated to two groups according to their tolerability to cold stimulation (cold pressor test, CPT, 1°C). Group LSP (N = 24) reached the cut-off time of 180±0 sec and group HSP tolerated the CPT for an average of 13±4.8 sec. Heat, cold and mechanical evoked pain were measured, as well as pain-catastrophizing (PCS), depression, anxiety and stress (DASS-21). All subjects underwent resting state fMRI. ROI-to-ROI analysis was performed.

RESULTS

In comparison to the LSP, the HSP had stronger interhemispheric connectivity of the amygdala (p = 0.01) and between the amygdala and nucleus accumbens (NAc) (p = 0.01). Amygdala connectivity was associated with higher pain catastrophizing in the HSP only (p<0.01).

CONCLUSIONS

These findings suggest that high sensitivity to pain may be reflected by neural circuits involved in affective and motivational aspects of pain. To what extent this connectivity within limbic brain structures relates to higher alertness and more profound withdrawal behavior to aversive events needs to be further investigated.

Red Nucleus Interleukin-6 Evokes Tactile Allodynia in Male Rats Through Modulating Spinal Pro-inflammatory and Anti-inflammatory Cytokines

Our previous studies have clarified that red nucleus (RN) interleukin (IL)-6 is involved in the maintenance of neuropathic pain and produces a facilitatory effect by activating JAK2/STAT3 and ERK pathways. In this study, we further explored the immune molecular mechanisms of rubral IL-6-mediated descending facilitation at the spinal cord level. IL-6-evoked tactile allodynia was established by injecting recombinant IL-6 into the unilateral RN of naive male rats. Following intrarubral administration of IL-6, obvious tactile allodynia was evoked in the contralateral hindpaw of rats. Meanwhile, the expressions of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), IL-1β, and IL-6 were elevated in the contralateral spinal dorsal horn (L4–L6), blocking spinal TNF-α, IL-1β, or IL-6 with neutralizing antibodies relieved IL-6-evoked tactile allodynia. Conversely, the levels of anti-inflammatory cytokines transforming growth factor-β (TGF-β) and IL-10 were reduced in the contralateral spinal dorsal horn (L4–L6), an intrathecal supplement of exogenous TGF-β, or IL-10 attenuated IL-6-evoked tactile allodynia. Further studies demonstrated that intrarubral pretreatment with JAK2/STAT3 inhibitor AG490 suppressed the elevations of spinal TNF-α, IL-1β, and IL-6 and promoted the expressions of TGF-β and IL-10 in IL-6-evoked tactile allodynia rats. However, intrarubral pretreatment with ERK inhibitor PD98059 only restrained the increase in spinal TNF-α and enhanced the expression of spinal IL-10. These findings imply that rubral IL-6 plays descending facilitation and produces algesic effect through upregulating the expressions of spinal pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 and downregulating the expressions of spinal anti-inflammatory cytokines TGF-β and IL-10 by activating JAK2/STAT3 and/or ERK pathways, which provides potential therapeutic targets for the treatment of pathological pain.

Volumetric differences in hippocampal subfields and associations with clinical measures in myalgic encephalomyelitis/chronic fatigue syndrome

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) patients suffer from a cognitive and memory dysfunction. Because the hippocampus plays a key role in both cognition and memory, we tested for volumetric differences in the subfields of the hippocampus in ME/CFS. We estimated hippocampal subfield volumes for 25 ME/CFS patients who met Fukuda criteria only (ME/CFS_Fukuda), 18 ME/CFS patients who met the stricter ICC criteria (ME/CFS_ICC), and 25 healthy controls (HC). Group comparisons with HC detected extensive differences in subfield volumes in ME/CFS_ICC but not in ME/CFS_Fukuda. ME/CFS_ICC patients had significantly larger volume in the left subiculum head (p < 0.001), left presubiculum head (p = 0.0020), and left fimbria (p = 0.004). Correlations of hippocampus subfield volumes with clinical measures were stronger in ME/CFS_ICC than in ME/CFS_Fukuda patients. In ME/CFS_Fukuda patients, we detected positive correlations between fatigue and hippocampus subfield volumes and a negative correlation between sleep disturbance score and the right CA1 body volume. In ME/CFS_ICC patients, we detected a strong negative relationship between fatigue and left hippocampus tail volume. Strong negative relationships were also detected between pain and SF36 physical scores and two hippocampal subfield volumes (left: GC‐ML‐DG head and CA4 head). Our study demonstrated that volumetric differences in hippocampal subfields have strong statistical inference for patients meeting the ME/CFS_ICC case definition and confirms hippocampal involvement in the cognitive and memory problems of ME/CFS_ICC patients.

Asymmetric Lateralization during Pain Processing

Pain is defined as “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage”. This complex perception arises from the coordinated activity of several brain areas processing either sensory–discriminative or affective–motivational components. Functional studies performed in healthy volunteers revealed that affective–emotional components of pain are processed bilaterally but present a clear lateralization towards the right hemisphere, regardless of the site of stimulation. Studies at the cellular level performed in experimental animal models of pain have shown that neuronal activity in the right amygdala is clearly pronociceptive, whilst activation of neurons in the left amygdala might even exert antinociceptive effects. A shift in lateralization becomes evident during the development of chronic pain; thus, in patients with neuropathic pain symptoms, there is increased activity in ipsilateral brain areas related with pain. These observations extend the asymmetrical left–right lateralization within the nervous system and provide a new hypothesis for the pathophysiology of chronic forms of pain. In this article, we will review experimental data from preclinical and human studies on functional lateralization in the brain during pain processing, which will help to explain the affective disorders associated with persistent, chronic pain.

Whole-brain morphological alterations associated with trigeminal neuralgia

Background

Novel neuroimaging strategies have the potential to offer new insights into the mechanistic basis for trigeminal neuralgia (TN). The present study aims to conduct whole-brain morphometry analyses of TN patients and to assess the value of group-level neocortical and subcortical structural patterns as tools for diagnostic biomarker exploration.

Methods

Cortical thickness, surface area, and myelin levels in the neocortex were measured via magnetic resonance imaging (MRI). The radial distance and the Jacobian determinant of the subcortex in 43 TN patients and 43 matched controls were compared. Pattern learning algorithms were employed to establish the utility of group-level MRI findings as tools for predicting TN. An additional 40 control patients with hemifacial spasms were then evaluated to assess algorithm sensitivity and specificity.

Results

TN patients exhibited reductions in cortical indices in the anterior cingulate cortex (ACC), the midcingulate cortex (MCC), and the posterior cingulate cortex (PCC) relative to controls. They further presented with widespread subcortical volume reduction that was most evident in the putamen, the thalamus, the accumbens, the pallidum, and the hippocampus. Whole brain-level morphological alterations successfully enable automated TN diagnosis with high specificity (TN: 95.35 %; disease controls: 46.51 %).

Conclusions

TN is associated with a distinctive whole-brain structural neuroimaging pattern, underscoring the value of machine learning as an approach to differentiating between morphological phenotypes, ultimately revealing the full spectrum of this disease and highlighting relevant diagnostic biomarkers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-021-01308-5.

Input-dependent synaptic suppression by pregabalin in the central amygdala in male mice with inflammatory pain

Pregabalin (PGB) is a synthetic amino acid compound most widely prescribed for chronic peripheral and central neuropathic pain. PGB is a ligand for the α2δ1 subunit of voltage-dependent calcium channels, and its binding reduces neurotransmitter release and thus inhibits synaptic transmission. The central nucleus of the amygdala (CeA) is a kernel site for the enhanced nociception-emotion link in chronic pain. The nociceptive information is conveyed to the CeA via the following two pathways: 1) the pathway arising from the basolateral amygdala (BLA), which carries nociceptive information mediated by the thalamocortical system, and 2) that arising from the external part of the pontine lateral parabrachial nucleus (LPB), that forms the final route of the spino-parabrachio-amygdaloid pathway that conveys nociceptive information directly from the superficial layer of the spinal dorsal horn. We compared the effects of PGB on the excitatory postsynaptic currents of neurons in the right CeA in response to electrical stimulation of BLA and LPB pathways using the whole-cell patch-clamp technique. Inflammatory pain was induced by intraplantar injection of formalin solution at the left hind paw. At eight hours post-formalin, PGB reduced EPSCs amplitude of the BLA-to-CeA synaptic transmission, accompanied by a significant increase in the PPR, suggesting a decreased release probability from the presynaptic terminals. In addition, these effects of PGB were only seen in inflammatory conditions. PGB did not affect the synaptic transmission at the LPB-to-CeA pathway, even in formalin-treated mice. These results suggest PGB improves not simply the aberrantly enhanced nociception but also various pain-associated cognitive and affective consequences in patients with chronic nociplastic pain.

Red nucleus IL-33 facilitates the early development of mononeuropathic pain in male rats by inducing TNF-α through activating ERK, p38 MAPK, and JAK2/STAT3

Background

Our recent studies have identified that the red nucleus (RN) dual-directionally modulates the development and maintenance of mononeuropathic pain through secreting proinflammatory and anti-inflammatory cytokines. Here, we further explored the action of red nucleus IL-33 in the early development of mononeuropathic pain.

Methods

In this study, male rats with spared nerve injury (SNI) were used as mononeuropathic pain model. Immunohistochemistry, Western blotting, and behavioral testing were used to assess the expressions, cellular distributions, and actions of red nucleus IL-33 and its related downstream signaling molecules.

Results

IL-33 and its receptor ST2 were constitutively expressed in the RN in naive rats. After SNI, both IL-33 and ST2 were upregulated significantly at 3 days and peaked at 1 week post-injury, especially in RN neurons, oligodendrocytes, and microglia. Blockade of red nucleus IL-33 with anti-IL-33 neutralizing antibody attenuated SNI-induced mononeuropathic pain, while intrarubral administration of exogenous IL-33 evoked mechanical hypersensitivity in naive rats. Red nucleus IL-33 generated an algesic effect in the early development of SNI-induced mononeuropathic pain through activating NF-κB, ERK, p38 MAPK, and JAK2/STAT3, suppression of NF-κB, ERK, p38 MAPK, and JAK2/STAT3 with corresponding inhibitors markedly attenuated SNI-induced mononeuropathic pain or IL-33-evoked mechanical hypersensitivity in naive rats. Red nucleus IL-33 contributed to SNI-induced mononeuropathic pain by stimulating TNF-α expression, which could be abolished by administration of inhibitors against ERK, p38 MAPK, and JAK2/STAT3, but not NF-κB.

Conclusions

These results suggest that red nucleus IL-33 facilitates the early development of mononeuropathic pain through activating NF-κB, ERK, p38 MAPK, and JAK2/STAT3. IL-33 mediates algesic effect partly by inducing TNF-α through activating ERK, p38 MAPK and JAK2/STAT3.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02198-9.

TRPV1 Responses in the Cerebellum Lobules VI, VII, VIII Using Electroacupuncture Treatment for Chronic Pain and Depression Comorbidity in a Murine Model

Depression is a prominent complex psychiatric disorder, usually complicated through expression of comorbid conditions, with chronic pain being among the most prevalent. This comorbidity is consistently associated with a poor prognosis and has been shown to negatively impact patient outcomes. With a global rise in this condition presenting itself, the importance of discovering long-term, effective, and affordable treatments is crucial. Electroacupuncture has demonstrated renowned success in its use for the treatment of pain and is a widely recognized therapy in clinical practice for the treatment of various psychosomatic disorders, most notably depression. Our study aimed to investigate the effects and mechanisms of Acid-Saline (AS) inducing states of chronic pain and depression comorbidity in the cerebellum, using the ST36 acupoint as the therapeutic intervention. Furthermore, the role of TRPV1 was relatedly explored through the use of TRPV1^−/− mice (KO). The results indicated significant differences in the four behavioral tests used to characterize pain and depression states in mice. The AS and AS + SHAM group showed significant differences when compared to the Control and AS + EA groups in the von Frey and Hargreaves’s tests, as well as the Open-Field and Forced Swimming tests. This evidence was further substantiated in the protein levels observed in immunoblotting, with significant differences between the AS and AS + SHAM groups when compared to the AS + EA and AS + KO groups being identified. In addition, immunofluorescence visibly served to corroborate the quantitative outcomes. Conclusively these findings suggest that AS-induced chronic pain and depression comorbidity elicits changes in the cerebellum lobules VI, VII, VIII, which are ameliorated through the use of EA at ST36 via its action on TRPV1 and related molecular pathways. The action of TRPV1 is not singular in CPDC, which would suggest other potential targets such as acid-sensing ion channel subtype 3 (ASIC3) or voltage-gated sodium channels (Navs) that could be explored in future studies.

Dopamine Inputs from the Ventral Tegmental Area into the Medial Prefrontal Cortex Modulate Neuropathic Pain-Associated Behaviors in Mice

The medial prefrontal cortex (mPFC) is a brain region involved in the affective components of pain and undergoes plasticity during the development of chronic pain. Dopamine (DA) is a key neuromodulator in the mesocortical circuit and modulates working memory and aversion. Although DA inputs into the mPFC are known to modulate plasticity, whether and how these inputs affect pain remains incompletely understood. By using optogenetics, we find that phasic activation of DA inputs from the ventral tegmental area (VTA) into the mPFC reduce mechanical hypersensitivity during neuropathic pain states. Mice with neuropathic pain exhibit a preference for contexts paired with photostimulation of DA terminals in the mPFC. Fiber photometry-based calcium imaging reveals that DA increases the activity of mPFC neurons projecting to the ventrolateral periaqueductal gray (vlPAG). Together, our findings indicate an important role of mPFC DA signaling in pain modulation.

Detangling red hair from pain: phenotype-specific contributions from different genetic variants in melanocortin-1 receptor

Genetic variation in melanocortin-1 receptor (MC1R) has a known role in red hair. Studies on responses to noxious stimuli in red-haired individuals have also been conducted, with mixed findings. To investigate a possible divergence between variants responsible for red hair and pain sensitivity, we performed a genewide association analysis in the Orofacial Pain: Prospective Evaluation and Risk Assessment cohort. All genotyped (17) MC1R variants were tested for association with heat pain temporal summation and sensitivity. Our analyses showed an association for pain sensitivity with the 5'-UTR, tagged by rs3212361, and 1 missense variant, rs885479 (R163Q), previously shown to be weakly associated with red hair. For both variants, the minor allele was protective. These results were validated in the 500,000-person UK Biobank cohort, where the minor alleles of rs3212361 and rs885479 were associated with a reduced count of persistent pain conditions as well as individual pain conditions. Haplotype association analysis revealed a possible joint effect from the 2 individual variants. The 5'-UTR variant rs3212361 was further identified as an expression quantitative trait locus, associated with reduced transcript levels of MC1R in the brain and in the peripheral tibial nerve. Hair colour association analysis of the loss-of-function 5'-UTR rs3212361 allele identified association with red hair, and red hair colour itself was associated with a reduced count of persistent pain conditions. Together, our results suggest that primarily different mechanisms-affecting expression levels vs protein activity-mediated by different genetic variants in the MC1R locus contribute to red hair and pain.

Replication of Previous Findings? Comparing Gray Matter Volumes in Transgender Individuals with Gender Incongruence and Cisgender Individuals

The brain structural changes related to gender incongruence (GI) are still poorly understood. Previous studies comparing gray matter volumes (GMV) between cisgender and transgender individuals with GI revealed conflicting results. Leveraging a comprehensive sample of transmen (n = 33), transwomen (n = 33), cismen (n = 24), and ciswomen (n = 25), we employ a region-of-interest (ROI) approach to examine the most frequently reported brain regions showing GMV differences between trans- and cisgender individuals. The primary aim is to replicate previous findings and identify anatomical regions which differ between transgender individuals with GI and cisgender individuals. On the basis of a comprehensive literature search, we selected a set of ROIs (thalamus, putamen, cerebellum, angular gyrus, precentral gyrus) for which differences between cis- and transgender groups have been previously observed. The putamen was the only region showing significant GMV differences between cis- and transgender, across previous studies and the present study. We observed increased GMV in the putamen for transwomen compared to both transmen and ciswomen and for all transgender participants compared to all cisgender participants. Such a pattern of neuroanatomical differences corroborates the large majority of previous studies. This potential replication of previous findings and the known involvement of the putamen in cognitive processes related to body representations and the creation of the own body image indicate the relevance of this region for GI and its potential as a structural biomarker for GI.

Mindfulness-based stress reduction training modulates striatal and cerebellar connectivity

Mindfulness is a meditation practice frequently associated with changes in subjective evaluation of cognitive and sensorial experience, as well as with modifications of brain activity and morphometry. Aside from the anatomical localization of functional changes induced by mindfulness practice, little is known about changes in functional and effective functional magnetic resonance imaging (fMRI) connectivity. Here we performed a connectivity fMRI analysis in a group of healthy individuals participating in an 8-week mindfulness-based stress reduction (MBSR) training program. Data from both a "mind-wandering" and a "meditation" state were acquired before and after the MBSR course. Results highlighted decreased local connectivity after training in the right anterior putamen and insula during spontaneous mind-wandering and the right cerebellum during the meditative state. A further effective connectivity analysis revealed (a) decreased modulation by the anterior cingulate cortex over the anterior portion of the putamen, and (b) a change in left and right posterior putamen excitatory input and inhibitory output with the cerebellum, respectively. Results suggest a rearrangement of dorsal striatum functional and effective connectivity in response to mindfulness practice, with changes in cortico-subcortical-cerebellar modulatory dynamics. Findings might be relevant for the understanding of widely documented mindfulness behavioral effects, especially those related to pain perception.

Foot shock facilitates reward seeking in an experience-dependent manner

Animals organize reward seeking around aversive events. An abundance of research shows that foot shock, as well as a shock-associated cue, can elicit freezing and suppress reward seeking. Yet, there is evidence that experience can flip the effect of foot shock to facilitate reward seeking. Here we examined cue suppression, foot shock suppression and foot shock facilitation of reward seeking in a single behavioural setting. Male Long Evans rats received fear discrimination consisting of danger, uncertainty, and safety cues. Discrimination took place over a baseline of rewarded nose poking. With limited experience (1-2 sessions), all cues and foot shock suppressed reward seeking. With continued experience (10-16 sessions), suppression became specific to shock-associated cues, foot shock briefly suppressed, then facilitated reward seeking. Our results provide a means of assessing positive properties of foot shock, and may provide insight into maladaptive behaviour around aversive events.

Effects of α7 Nicotinic Acetylcholine Receptor Positive Allosteric Modulator on BDNF, NKCC1 and KCC2 Expression in the Hippocampus following Lipopolysaccharide-Induced Allodynia and Hyperalgesia in a Mouse Model of Inflammatory Pain

BACKGROUND & OBJECTIVES

Hyperalgesia and allodynia are frequent symptoms of inflammatory pain. Neuronal excitability induced by the Brain-Derived Neurotrophic Factor (BDNF)-tyrosine receptor kinase B (TrkB) cascade has a role in the modulation of inflammatory pain. The effects of 3a,4,5,9b-tetrahydro-4-(1-naphthalenyl)-3H-cyclopentan[c]quinoline-8-sulfonamide (TQS), an α7 nicotinic Acetylcholine Receptor Positive Allosteric Modulator (nAChR PAM), on hippocampal BDNF, cation-chloride cotransporters, NKCC1 and KCC2, expression in inflammatory pain are not known. The objective of the study was to determine the effects of TQS on BDNF, NKCC1, and KCC2 expression in the hippocampus following lipopolysaccharide (LPS)-induced allodynia and hyperalgesia in a mouse model of inflammatory pain.

METHODS

Mice were treated with TQS followed by LPS (1 mg/kg, ip) administration. The effects of TQS on mRNA and BDNF in the hippocampus were examined using qRT-PCR and Western blot, respectively. Immunoreactivity of BDNF, NKCC1, and KCC2 in the hippocampus was measured after LPS administration using immunofluorescence assay. Allodynia and hyperalgesia were determined using von Frey filaments and hot plate, respectively.

RESULTS

The LPS (1 mg/kg) upregulates mRNA of BDNF and downregulates mRNA of KCC2 in the hippocampus and pretreatment of TQS (4 mg/kg) reversed the effects induced by LPS. In addition, the TQS decreased LPS-induced upregulation of BDNF and p-NKCC1 immunoreactivity in the dentate gyrus and CA1 region of the hippocampus. BDNF receptor (TrkB) antagonist, ANA12 (0.50 mg/kg), and NKCC1 inhibitor bumetanide (30 mg/kg) reduced LPS-induced allodynia and hyperalgesia. Blockade of TrkB with ANA12 (0.25 mg/kg) enhanced the effects of TQS (1 mg/kg) against LPS-induced allodynia and hyperalgesia. Similarly, bumetanide (10 mg/kg) enhanced the effects of TQS (1 mg/kg) against allodynia and hyperalgesia.

CONCLUSION

These results suggest that antinociceptive effects of α7 nAChR PAM are associated with downregulation of hippocampal BDNF and p-NKCC1 and upregulation of KCC2 in a mouse model of inflammatory pain.

Harmaline potentiates morphine-induced antinociception via affecting the ventral hippocampal GABA-A receptors in mice

Morphine is one of the most effective medications for treatment of pain, but its side effects limit its use. Therefore, identification of new strategies that can enhance morphine-induced antinociception and/or reduce its side effects will help to develop therapeutic approaches for pain relief. Considering antinociceptive efficacy of harmaline and also highlighted the important role of GABA-A receptors in the pain perception, this research aimed to determine whether the ventral hippocampal (vHip) GABA-A receptors are involved in the possible harmaline-induced enhancement of morphine antinociception. To achieve this, vHip regions of adult male mice were bilaterally cannulated and pain sensitivity was measured in a tail-flick apparatus. Intraperitoneally administration of morphine (0, 2, 4 and 6 mg/kg) or harmaline (0, 1.25, 5 and 10 mg/kg) increased the percentage of maximal possible effect (%MPE) and induced antinociception. Interestingly, co-administration of sub-effective doses of harmaline (5 mg/kg) and morphine (2 mg/kg) induced antinociception. Intra-vHip microinjection of muscimol (0, 200 and 300 ng/mice), a GABA-A receptor agonist, enhanced the anti-nociceptive effects of harmaline (2.5 mg/kg)+morphine (2 mg/kg) combination. Microinjection of the same doses of muscimol into the vHip by itself did not alter tail-flick latency. Intra-vHip microinjection of bicuculline (100 ng/mouse), a GABA-A receptor antagonist, did not cause a significant change in MPE%. Bicuculline (60 and 100 ng/mouse, intra-vHip) was administered with the harmaline (5 mg/kg)+morphine (2 mg/kg), and inhibited the potentiating effect of harmaline on morphine response. These findings favor the notion that GABAergic mechanisms in the vHip facilitate harmaline-induced potentiation of morphine response in the tail-flick test in part through GABA-A receptors. These findings shall provide insights and strategies into the development of pain suppressing drugs.

A Deep Spatial Context Guided Framework for Infant Brain Subcortical Segmentation

Accurate subcortical segmentation of infant brain magnetic resonance (MR) images is crucial for studying early subcortical structural growth patterns and related diseases diagnosis. However, dynamic intensity changes, low tissue contrast, and small subcortical size of infant brain MR images make subcortical segmentation a challenging task. In this paper, we propose a spatial context guided, coarse-to-fine deep convolutional neural network (CNN) based framework for accurate infant subcortical segmentation. At the coarse stage, we propose a signed distance map (SDM) learning UNet (SDM-UNet) to predict SDMs from the original multi-modal images, including T1w, T2w, and T1w/T2w images. By doing this, the spatial context information, including the relative position information across different structures and the shape information of the segmented structures contained in the ground-truth SDMs, is used for supervising the SDM-UNet to remedy the bad influence from the low tissue contrast in infant brain MR images and generate high-quality SDMs. To improve the robustness to outliers, a Correntropy based loss is introduced in SDM-UNet to penalize the difference between the ground-truth SDMs and predicted SDMs in training. At the fine stage, the predicted SDMs, which contains spatial context information of subcortical structures, are combined with the multi-modal images, and then fed into a multi-source and multi-path UNet (M2-UNet) for delivering refined segmentation. We validate our method on an infant brain MR image dataset with 24 scans by evaluating the Dice ratio between our segmentation and the manual delineation. Compared to four state-of-the-art methods, our method consistently achieves better performances in both qualitative and quantitative evaluations.

The medial temporal lobe in nociception: a meta-analytic and functional connectivity study

Recent neuroimaging studies implicate the medial temporal lobe (MTL) in nociception and pain modulation. Here, we aim to identify which subregions of the MTL are involved in human pain and to test its connectivity in a cohort of chronic low-back pain patients (CBP). We conducted 2 coordinate-based meta-analyses to determine which regions within the MTL showed consistent spatial patterns of functional activation (1) in response to experimental pain in healthy participants and (2) in chronic pain compared with healthy participants. We followed PRISMA guidelines and performed activation likelihood estimate (ALE) meta-analyses. The first meta-analysis revealed consistent activation in the right anterior hippocampus (right antHC), parahippocampal gyrus, and amygdala. The second meta-analysis revealed consistently less activation in patients' right antHC, compared with healthy participants. We then conducted a seed-to-voxel resting state functional connectivity of the right antHC seed with the rest of the brain in 77 CBP and 79 age-matched healthy participants. We found that CBP had significantly weaker antHC functional connectivity to the medial prefrontal cortex compared with healthy participants. Taken together, these data indicate that the antHC has abnormally lower activity in chronic pain and reduced connectivity to the medial prefrontal cortex in CBP. Future studies should investigate the specific role of the antHC in the development and management of chronic pain.

Amygdala physiology in pain

The amygdala has emerged as an important brain area for the emotional-affective dimension of pain and pain modulation. The amygdala receives nociceptive information through direct and indirect routes. These excitatory inputs converge on the amygdala output region (central nucleus) and can be modulated by inhibitory elements that are the target of (prefrontal) cortical modulation. For example, inhibitory neurons in the intercalated cell mass in the amygdala project to the central nucleus to serve gating functions, and so do inhibitory (PKCdelta) interneurons within the central nucleus. In pain conditions, synaptic plasticity develops in output neurons because of an excitation-inhibition imbalance and drives pain-like behaviors and pain persistence. Mechanisms of pain related neuroplasticity in the amygdala include classical transmitters, neuropeptides, biogenic amines, and various signaling pathways. An emerging concept is that differences in amygdala activity are associated with phenotypic differences in pain vulnerability and resilience and may be predetermining factors of the complexity and persistence of pain.

Multiple Brain Networks Mediating Stimulus-Pain Relationships in Humans

The brain transforms nociceptive input into a complex pain experience comprised of sensory, affective, motivational, and cognitive components. However, it is still unclear how pain arises from nociceptive input and which brain networks coordinate to generate pain experiences. We introduce a new high-dimensional mediation analysis technique to estimate distributed, network-level patterns that formally mediate the relationship between stimulus intensity and pain. We applied the model to a large-scale analysis of functional magnetic resonance imaging data (N = 284), focusing on brain mediators of the relationship between noxious stimulus intensity and trial-to-trial variation in pain reports. We identify mediators in both traditional nociceptive pathways and in prefrontal, midbrain, striatal, and default-mode regions unrelated to nociception in standard analyses. The whole-brain mediators are specific for pain versus aversive sounds and are organized into five functional networks. Brain mediators predicted pain ratings better than previous brain measures, including the neurologic pain signature (Wager et al. 2013). Our results provide a broader view of the networks underlying pain experience, as well as novel brain targets for interventions.

Brain Metabolism in Rats with Neuropathic Pain Induced by Brachial Plexus Avulsion Injury and Treated via Electroacupuncture

PURPOSE

Brain organisation is involved in the mechanism of neuropathic pain. Acupuncture is a common clinical practise in traditional Chinese medicine for the treatment of chronic pain. This study explored electroacupuncture's effects on brain metabolism following brachial plexus avulsion injury (BPAI)-induced pain.

METHODS

A total of 32 female rats were randomised into a normal group, model group, sham electroacupuncture group, and electroacupuncture group. A pain model was included via right BPAI. The electroacupuncture intervention at cervical "Jiaji" points (C5-7) was performed for 11 weeks. The mechanical withdrawal threshold of the non-injured (left) forepaw was measured at the baseline and on days 3, 7, 14, 21, 28, 56, 84, and 112 subsequent to BPAI. Positron emission tomography (PET) was applied to explore metabolic changes on days 28, 84, and 112.

RESULTS

After electroacupuncture, the mechanical withdrawal threshold of the left forepaws was significantly elevated and the effect persisted until 4 weeks after the intervention ceased (p<0.05 or p<0.001). In the sensorimotor-related brain regions, standardised uptake values in the bilateral somatosensory and motor cortices were observed in the electroacupuncture group. Metabolism particularly increased in the right somatosensory cortex. Metabolism changes also occurred in the pain-related brain regions and emotion- and cognition-related brain regions.

CONCLUSION

The present study demonstrated the beneficial effects of electroacupuncture for relieving BPAI-induced neuropathic pain in rats. Electroacupuncture intervention might inhibit maladaptive plasticity in brain areas governing multidimensional functions, especially in sensorimotor- and cognition-related cortices.

Somatic complaints in early adulthood predict the developmental course of compassion into middle age

OBJECTIVE

The aim of the present study was to investigate (i) whether somatic complaints predict the developmental course of compassion in adulthood, and (ii) whether this association depends on alexithymic features.

METHODS

The participants came from the population-based Young Finns study (N = 471-1037). Somatic complaints (headache, stomachache, chest pain, backache, fatigue, exhaustion, dizziness, heartburn, heartbeat, and tension) were evaluated with a self-rating questionnaire in 1986 when participants were aged between 18 and 24 years. Compassion was assessed with the Compassion Scale of the Temperament and Character Inventory (TCI) in 1997, 2001, and 2012. The data were analyzed using growth curve models.

RESULTS

We obtained a significant compassion-age interaction (B = -0.137, p = .02) and a compassion-age squared interaction (B = 0.007, p = .006), when predicting the course of somatic complaints. Specifically, in participants without frequent somatic complaints, compassion steadily increased with age in adulthood. In participants with frequent somatic complaints, however, compassion remained at a lower level until the age of 40 years, then started to increase, and achieved the normal level of compassion approximately at the age of 50 years. The association between somatic complaints and compassion over age was found to be independent of alexithymic features. The analyses were adjusted for a variety of covariates (age, gender, use of health care in childhood, depression in childhood, parental socioeconomic factors, parental care-giving practices, stressful life events, parental alcohol intoxication, and participants' socioeconomic factors in adulthood).

CONCLUSION

Frequent somatic complaints may predict delayed development of compassion in adulthood. This association was found to be independent of alexithymic features.

The α7 nicotinic acetylcholine receptor positive allosteric modulator prevents lipopolysaccharide-induced allodynia, hyperalgesia and TNF-α in the hippocampus in mice

BACKGROUND

Previous studies have shown that α7 nicotinic acetylcholine receptor (nAChR) has a critical role in the regulation of pain sensitivity and neuroinflammation. However, pharmacological effects of α7 nAChR activation in the hippocampus on neuroinflammatory mechanisms associated with allodynia and hyperalgesia remain unknown. We have determined the effects of 3a,4,5,9b-tetrahydro-4-(1-naphthalenyl)-3H-cyclopentan[c]quinoline-8-sulfonamide (TQS), an α7 nAChR positive allosteric modulator, on lipopolysaccharide (LPS)-induced allodynia and hyperalgesia in mice. We also evaluated the effects of TQS on immunoreactivity of microglial marker ionized-calcium binding adaptor molecule 1 (Iba-1), phospho-nuclear factor-κB (p-NF-κB p65), tumor necrosis factor-alpha (TNF-α), and norepinephrine (NE) level.

METHODS

Mice were treated with (0.25, 1 or 4 mg/kg, ip) followed by LPS (1 mg/kg, ip) administration. Allodynia and hyperalgesia were determined using von Frey filaments and hot plate respectively. Immunoreactivity of Iba-1, p-NF-κB p65, and TNF-α, were measured in the hippocampus using immunofluorescence assay. Hippocampal NE level was evaluated using high performance liquid chromatography.

RESULTS

LPS administration resulted in allodynia and hyperalgesia in mice after six h. Systemic administration of TQS prevented LPS-induced allodynia and hyperalgesia. TQS pretreatment significantly decreased the immunoreactivity of Iba-1, p-NF-κB, and TNF-α in CA1 and DG regions of the hippocampus. In addition, TQS reversed LPS-induced NE reduction in the hippocampus.

CONCLUSIONS

Taken together, our results suggest that TQS prevented LPS-induced allodynia and hyperalgesia, upregulation of TNF-α expression and NE level reduction involving microglial α7 nAChR in part in the hippocampus. Therefore, these findings highlight the important effects of α7 nAChR allosteric modulator against symptoms of inflammatory pain.

Modular organization of brain resting state networks in patients with classical trigeminal neuralgia

•

Sensorimotor network and default mode network activities were lower in trigeminal neuralgia patients and increased after surgery.

•

Higher communication between the default mode network module and other modules before surgery was associated with better treatment response.

•

Subcortical modules was associated with pain duration.

•

A lower connection between the default mode network and subcortical modules was associated with a better treatment response and the thalamus and midcingulate cortex were the major connectors within the subcortical module.

Background

The modular organization of brain networks in trigeminal neuralgia patients has remained largely unknown. We aimed to analyze the brain modules and intermodule connectivity in patients with trigeminal neuralgia before and after percutaneous radiofrequency rhizotomy treatment to identify specific modules that may be associated with the development and brain plasticity of trigeminal neuralgia and to test the ability of modularity analysis to be a predictive imaging biomarker for the treatment effect in patients with trigeminal neuralgia.

Methods

A total of 25 patients with right trigeminal neuralgia and 20 matched healthy subjects were included. Blood-oxygen-level dependent resting state fMRI was used to analyze the brain modular organization.

Results

Whole brain modularity analysis identified seven modules. The metric of intermodule connectivity, participation coefficient, of the sensorimotor network and default mode network modules were significantly lower in patients and increased after surgery. The participation coefficient of the subcortical modules was associated with the pain duration. Higher communication between the default mode network module and other modules before surgery was associated with a better treatment response. Furthermore, the subcortical module was a significant contributor to the participation coefficient relationship of the default mode network module with the treatment response, and the bilateral midcingulate cortex and thalamus were major connectors in the subcortical module.

Conclusions

These findings have important implications regarding the global brain modular responses to chronic neuropathic pain and it may be feasible to use the modularity analysis as part of a risk stratification to predict the treatment response.

Subcortical structural abnormalities in female neuromyelitis optica patients with neuropathic pain

Neuromyelitis optica (NMO) is a disease characterised by severe relapses of optic neuritis and longitudinally extensive transverse myelitis and it has a strong female predilection. Pain is one of the most typical symptom in NMO. However, few studies have been conducted to examine the neuropathic pain mechanism of NMO patients or gender-specific effects using magnetic resonance imaging technique. A total of 38 female patients with NMO, 28 with pain (NMOWP) and 10 without pain (NMOWoP), were classified using the Brief Pain Inventory (BPI); 22 healthy females were also recruited. We used the FSL Image Registration and Segmentation Toolbox (FIRST) for subcortical region volumes quantifications, and voxel-based morphometry analysis for cortical gray matter (GM) volume, to examine the brain morphology in NMOWP patients. In addition, correlation test between structural measurements of NMO patients and clinical indexes was also performed. The results showed: 1) no significant differences in cortical GM density between the NMOWP and NMOWoP groups; 2) significantly smaller hippocampus and pallidum volumes in the NMOWP group compared with the NMOWoP group; 3) significant negative correlation between the average BPI and volumes of the accumbens nucleus and thalamus in NMO patients. These results revealed that structural abnormality exists in NMO female patients who have pain, with significant implications for our understanding of the brain morphology in NMO patients with pain.

Different brain networks mediate the effects of social and conditioned expectations on pain

Information about others' experiences can strongly influence our own feelings and decisions. But how does such social information affect the neural generation of affective experience, and are the brain mechanisms involved distinct from those that mediate other types of expectation effects? Here, we used fMRI to dissociate the brain mediators of social influence and associative learning effects on pain. Participants viewed symbolic depictions of other participants' pain ratings (social information) and classically conditioned pain-predictive cues before experiencing painful heat. Social information and conditioned stimuli each had significant effects on pain ratings, and both effects were mediated by self-reported expectations. Yet, these effects were mediated by largely separable brain activity patterns, involving different large-scale functional networks. These results show that learned versus socially instructed expectations modulate pain via partially different mechanisms-a distinction that should be accounted for by theories of predictive coding and related top-down influences.

Delineating conditions and subtypes in chronic pain using neuroimaging

Differentiating subtypes of chronic pain still remains a challenge—both from a subjective and objective point of view. Personalized medicine is the current goal of modern medical care and is limited by the subjective nature of patient self-reporting of symptoms and behavioral evaluation. Physiology-focused techniques such as genome and epigenetic analyses inform the delineation of pain groups; however, except under rare circumstances, they have diluted effects that again, share a common reliance on behavioral evaluation. The application of structural neuroimaging towards distinguishing pain subtypes is a growing field and may inform pain-group classification through the analysis of brain regions showing hypertrophic and atrophic changes in the presence of pain. Analytical techniques such as machine-learning classifiers have the capacity to process large volumes of data and delineate diagnostically relevant information from neuroimaging analysis. The issue of defining a “brain type” is an emerging field aimed at interpreting observed brain changes and delineating their clinical identity/significance. In this review, 2 chronic pain conditions (migraine and irritable bowel syndrome) with similar clinical phenotypes are compared in terms of their structural neuroimaging findings. Independent investigations are compared with findings from application of machine-learning algorithms. Findings are discussed in terms of differentiating patient subgroups using neuroimaging data in patients with chronic pain and how they may be applied towards defining a personalized pain signature that helps segregate patient subgroups (eg, migraine with and without aura, with or without nausea; irritable bowel syndrome vs other functional gastrointestinal disorders).

Memory for non-painful auditory items is influenced by whether they are experienced in a context involving painful electrical stimulation

In this study, we sought to examine the effect of experimentally induced somatic pain on memory. Subjects heard a series of words and made categorization decisions in two different conditions. One condition included painful shocks administered just after presentation of some of the words; the other condition involved no shocks. For the condition that included painful stimulations, every other word was followed by a shock, and subjects were informed to expect this pattern. Word lists were repeated three times within each condition in randomized order, with different category judgments but consistent pain-word pairings. After a brief delay, recognition memory was assessed. Non-pain words from the pain condition were less strongly encoded than non-pain words from the completely pain-free condition. Recognition of pain-paired words was not significantly different than either subgroup of non-pain words. An important accompanying finding is that response times to repeated experimental items were slower for non-pain words from the pain condition, compared to non-pain words from the completely pain-free condition. This demonstrates that the effect of pain on memory may generalize to non-pain items experienced in the same experimental context.

Evidence for an association of gut microbial Clostridia with brain functional connectivity and gastrointestinal sensorimotor function in patients with irritable bowel syndrome, based on tripartite network analysis

BACKGROUND AND AIMS

Evidence from preclinical and clinical studies suggests that interactions among the brain, gut, and microbiota may affect the pathophysiology of irritable bowel syndrome (IBS). As disruptions in central and peripheral serotonergic signaling pathways have been found in patients with IBS, we explored the hypothesis that the abundance of serotonin-modulating microbes of the order Clostridiales is associated with functional connectivity of somatosensory brain regions and gastrointestinal (GI) sensorimotor function.

METHODS

We performed a prospective study of 65 patients with IBS and 21 healthy individuals (controls) recruited from 2011 through 2013 at a secondary/tertiary care outpatient clinic in Sweden. Study participants underwent functional brain imaging, rectal balloon distension, a nutrient and lactulose challenge test, and assessment of oroanal transit time within a month. They also submitted stool samples, which were analyzed by 16S ribosomal RNA gene sequencing. A tripartite network analysis based on graph theory was used to investigate the interactions among bacteria in the order Clostridiales, connectivity of brain regions in the somatosensory network, and GI sensorimotor function.

RESULTS

We found associations between GI sensorimotor function and gut microbes in stool samples from controls, but not in samples from IBS patients. The largest differences between controls and patients with IBS were observed in the Lachnospiraceae incertae sedis, Clostridium XIVa, and Coprococcus subnetworks. We found connectivity of subcortical (thalamus, caudate, and putamen) and cortical (primary and secondary somatosensory cortices) regions to be involved in mediating interactions among these networks.

CONCLUSIONS

In a comparison of patients with IBS and controls, we observed disruptions in the interactions between the brain, gut, and gut microbial metabolites in patients with IBS-these involve mainly subcortical but also cortical regions of brain. These disruptions may contribute to altered perception of pain in patients with IBS and may be mediated by microbial modulation of the gut serotonergic system.

Gray matter correlates of pressure pain thresholds and self-rated pain sensitivity: a voxel-based morphometry study

Individual differences in sensitivity to pain are large and have clinical and scientific importance. Although heavily influenced by situational factors, they also relate to genetic factors and psychological traits, and are reflected by differences in functional activation in pain-related brain regions. Here, we used voxel-based morphometry to investigate if individual pain sensitivity is related to local gray matter volumes. Pain sensitivity was determined using (1) index finger pressure pain thresholds (PPTs) and (2) pain intensity ratings of imagined painful situations as assessed by the Pain Sensitivity Questionnaire (PSQ) in 501 population-based subjects participating in the BiDirect Study. Pain Sensitivity Questionnaire scores were positively associated with gray matter in 2 symmetrical clusters, with a focus on the parahippocampal gyrus, extending to the hippocampus, fusiform gyrus, BA19, putamen, and insula (P < 0.05 corrected), but the effect was small (R = 0.045-0.039). No negative associations with the PSQ and no associations with the PPT reached significance. Parahippocampal activation during pain and altered parahippocampal gray matter in chronic pain have been reported, which would be consistent with positive associations with PSQ scores. Alternatively, associations of PSQ scores with the parahippocampal and fusiform gray matter could relate to the visual imagination of painful situations required by the PSQ, not to pain sensitivity itself. Regarding PPTs, the present data obtained in a large sample strongly suggest an absence of associations of this parameter with gray matter volume. In conclusion, the present results argue against a strong association between pain sensitivity and local gray matter volumes.

Cerebral 18F-FDG metabolism alteration in a neuropathic pain model following brachial plexus avulsion: A PET/CT study in rats

The present study aimed to investigate cerebral metabolic changes in a neuropathic pain model following deafferentation. A total of 24 Sprague-Dawley rats were included for modeling of right brachial plexus avulsion (BPA) through the posterior approach. As nerve injury would cause central sensitization and facilitate pain sensitivity in other parts of the body, thermal withdrawal latency (TWL) of the intact forepaw was assessed to investigate the level of pain perception following BPA-induced neuropathic pain. [Fluorine-18]-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) positron emission tomography (PET) was applied to the brain before and after brachial plexus avulsion to explore metabolic changes in neuropathic pain following deafferentation. The TWL of the left (intact) forepaw was significantly lower after BPA than that of baseline (p < 0.001). Using TWL as a covariate, standardized uptake values (SUVs) of ¹⁸F-FDG significantly increased in the ipsilateral dorsolateral thalamus and contralateral anterodorsal hippocampus after BPA. Conversely, SUVs in multiple brain regions decreased, including the contralateral somatosensory cortex, ipsilateral cingulate cortex, and ipsilateral temporal association cortex. The Pearson correlation analysis showed that the SUVs of the contralateral anterodorsal hippocampus and ipsilateral dorsolateral thalamus were negatively related to the TWL of the intact forepaw, whereas the SUVs in the contralateral somatosensory cortex and ipsilateral cingulate cortex were positively related to it (p < 0.05). These findings indicate that upregulation of metabolism in the anterodorsal hippocampus and dorsolateral thalamus and downregulation metabolism in the contralateral somatosensory cortex and ipsilateral cingulate cortex could be a unique pattern of metabolic changes for neuropathic pain following brachial plexus avulsion.

Effects of glial glutamate transporter activator in formalin-induced pain behaviour in mice

BACKGROUND

Nociceptive pain remains a prevalent clinical problem and often poorly responsive to the currently available analgesics. Previous studies have shown that astroglial glutamate transporter-1 (GLT-1) in the hippocampus and anterior cingulate cortex (ACC) is critically involved in pain processing and modulation. However, the role of astroglial GLT-1 in nociceptive pain involving the hippocampus and ACC remains unknown. We investigated the role of 3-[[(2-Methylphenyl) methyl]thio]-6-(2-pyridinyl)-pyridazine (LDN-212320), a GLT-1 activator, in nociceptive pain model and hippocampal-dependent behavioural tasks in mice.

METHODS

We evaluated the effects of LDN-212320 in formalin-induced nociceptive pain model. In addition, formalin-induced impaired hippocampal-dependent behaviours were measured using Y-maze and object recognition test. Furthermore, GLT-1 expression and extracellular signal-regulated kinase phosphorylation (pERK1/2) were measured in the hippocampus and ACC using Western blot analysis and immunohistochemistry.

RESULTS

The LDN-212320 (10 or 20 mg/kg, i.p) significantly attenuated formalin-evoked nociceptive behaviour. The antinociceptive effects of LDN-212320 were reversed by systemic administration of DHK (10 mg/kg, i.p), a GLT-1 antagonist. Moreover, LDN-212320 (10 or 20 mg/kg, i.p) significantly reversed formalin-induced impaired hippocampal-dependent behaviour. In addition, LDN-212320 (10 or 20 mg/kg, i.p) increased GLT-1 expressions in the hippocampus and ACC. On the other hand, LDN-212320 (20 mg/kg, i.p) significantly reduced formalin induced-ERK phosphorylation, a marker of nociception, in the hippocampus and ACC.

CONCLUSION

These results suggest that the GLT-1 activator LDN-212320 prevents nociceptive pain by upregulating astroglial GLT-1 expression in the hippocampus and ACC. Therefore, GLT-1 activator could be a novel drug candidate for nociceptive pain.

SIGNIFICANCE

The present study provides new insights and evaluates the role of GLT-1 activator in the modulation of nociceptive pain involving hippocampus and ACC. Here, we provide evidence that GLT-1 activator could be a potential therapeutic utility for the treatment of nociceptive pain.

Somatosensory deficits

The analysis and interpretation of somatosensory information are performed by a complex network of brain areas located mainly in the parietal cortex. Somatosensory deficits are therefore a common impairment following lesions of the parietal lobe. This chapter summarizes the clinical presentation, examination, prognosis, and therapy of sensory deficits, along with current knowledge about the anatomy and function of the somatosensory system. We start by reviewing how somatosensory signals are transmitted to and processed by the parietal lobe, along with the anatomic and functional features of the somatosensory system. In this context, we highlight the importance of the thalamus for processing somatosensory information in the parietal lobe. We discuss typical patterns of somatosensory deficits, their clinical examination, and how they can be differentiated through a careful neurologic examination that allows the investigator to deduce the location and size of the underlying lesion. In the context of adaption and rehabilitation of somatosensory functions, we delineate the importance of somatosensory information for motor performance and the prognostic evaluation of somatosensory deficits. Finally, we review current rehabilitation approaches for directing cortical reorganization in the appropriate direction and highlight some challenging questions that are unexplored in the field.

Mouse MRI shows brain areas relatively larger in males emerge before those larger in females

Sex differences exist in behaviors, disease and neuropsychiatric disorders. Sexual dimorphisms however, have yet to be studied across the whole brain and across a comprehensive time course of postnatal development. Here, we use manganese-enhanced MRI (MEMRI) to longitudinally image male and female C57BL/6J mice across 9 time points, beginning at postnatal day 3. We recapitulate findings on canonically dimorphic areas, demonstrating MEMRI’s ability to study neuroanatomical sex differences. We discover, upon whole-brain volume correction, that neuroanatomical regions larger in males develop earlier than those larger in females. Groups of areas with shared sexually dimorphic developmental trajectories reflect behavioral and functional networks, and expression of genes involved with sex processes. Also, post-pubertal neuroanatomy is highly individualized, and individualization occurs earlier in males. Our results demonstrate the ability of MEMRI to reveal comprehensive developmental differences between male and female brains, which will improve our understanding of sex-specific predispositions to various neuropsychiatric disorders.

Sex differences occur in various aspects of neurodevelopment. Here the authors use manganese-enhanced MRI at nine different postnatal stages to detail the development of structural sex differences in the mouse brain.

Altered Brain Regional Homogeneity Following Electro-Acupuncture Stimulation at Sanyinjiao (SP6) in Women With Premenstrual Syndrome

Background: Premenstrual syndrome (PMS) is a menstrual cycle-related disorder which causes physical and mood changes prior to menstruation and is associated with the functional dysregulation of the brain. Acupuncture is an effective alternative therapy for treating PMS, and sanyinjiao (SP6) is one of the most common acupoints used for improving the symptoms of PMS. However, the mechanism behind acupuncture's efficacy for relieving PMS symptoms remains unclear. The aim of this study was to identify the brain response patterns induced by acupuncture at acupoint SP6 in patients with PMS. Materials and Methods: Twenty-three females with PMS were enrolled in this study. All patients underwent resting-state fMRI data collection before and after 6 min of electroacupuncture stimulation (EAS) at SP6. A regional homogeneity (ReHo) approach was used to compare patients' brain responses before and after EAS at SP6 using REST software. The present study was registered at http://www.chictr.org.cn, and the Clinical Trial Registration Number is ChiCTR-OPC-15005918. Results: EAS at SP6 elicited decreased ReHo value at the bilateral precuneus, right inferior frontal cortex (IFC) and left middle frontal cortex (MFC). In contrast, increased ReHo value was found at the bilateral thalamus, bilateral insula, left putamen and right primary somatosensory cortex (S1). Conclusions: Our study provides an underlying neuroimaging evidence that the aberrant neural activity of PMS patients could be regulated by acupuncture at SP6.

Cerebellar direct current stimulation modulates hand blink reflex: implications for defensive behavior in humans

The cerebellum is involved in a wide number of integrative functions. We evaluated the role of cerebellum in peripersonal defensive behavior, as assessed by the so-called hand blink reflex (HBR), modulating cerebellar activity with transcranial direct current stimulation (tDCS). Healthy subjects underwent cerebellar (sham, anodal, and cathodal tcDCS) and motor cortex tDCS (anodal or cathodal; 20', 2 mA). For the recording of HBR, electrical stimuli were delivered using a surface bipolar electrode placed on the median nerve at the wrist and EMG activity recorded from the orbicularis oculi muscle bilaterally. Depending on the hand position respective to the face, HBR was assessed in four different conditions: "hand-far," "hand-near" (eyes open), "side hand," and "hand-patched" (eyes closed). While sham and cathodal cerebellar stimulation had no significant effect, anodal tcDCS dramatically dampened the magnitude of the HBR, as measured by the area under the curve (AUC), in the "hand-patched" and "side hand" conditions only, for ipsilateral (F(4,171)  = 15.08, P < 0.0001; F(4,171)  = 8.95, P < 0.0001) as well as contralateral recordings (F(4,171)  = 17.96, P < 0.0001); F4,171)  = 5.35, P = 0.0004). Cerebellar polarization did not modify AUC in the "hand-far" and "hand-near" sessions. tDCS applied over the motor area did not affect HBR. These results seem to support a role of the cerebellum in the defensive responses within the peripersonal space surrounding the face, thus suggesting a possible cerebellar involvement in visual-independent defensive behavior.

Can a single pulse transcranial magnetic stimulation targeted to the motor cortex interrupt pain processing?

The modulatory role of the primary motor cortex (M1), reflected by an inhibitory effect of M1-stimulation on clinical pain, motivated us to deepen our understanding of M1’s role in pain modulation. We used Transcranial Magnetic Stimulation (TMS)-induced virtual lesion (VL) to interrupt with M1 activity during noxious heat pain. We hypothesized that TMS-VL will effect experimental pain ratings. Three VL protocols were applied consisting of single-pulse TMS to transiently interfere with right M1 activity: (1) VL_M1- TMS applied to 11 subjects, 20 msec before the individual’s first pain-related M1 peak activation, as determined by source analysis (sLORETA), (2) VL_-50 (N = 16; TMS applied 50 ms prior to noxious stimulus onset), and (3) VL₊₁₅₀ (N = 16; TMS applied 150 ms after noxious stimulus onset). Each protocol included 3 conditions ('pain-alone', ' TMS-VL', and ‘SHAM-VL’), each consisted of 30 noxious heat stimuli. Pain ratings were compared, in each protocol, for TMS-VL vs. SHAM-VL and vs. pain-alone conditions. Repeated measures analysis of variance, corrected for multiple comparisons revealed no significant differences in the pain ratings between the different conditions within each protocol. Therefore, our results from this exploratory study suggest that a single pulse TMS-induced VL that is targeted to M1 failed to interrupt experimental pain processing in the specific three stimulation timing examined here.