Where pain meets action in the human brain

Acute pain impairs retention of locomotor learning

Despite abundant evidence that pain alters movement performance, considerably less is known about the potential effects of pain on motor learning. Some of the brain regions involved in pain processing are also responsible for specific aspects of motor learning, indicating that the two functions have the potential to interact, yet it is unclear if they do. In experiment 1, we compared the acquisition and retention of a novel locomotor pattern in young, healthy individuals randomized to either experience pain via capsaicin and heat applied to the lower leg during learning or no stimulus. On day 1, participants learned a new asymmetric walking pattern using distorted visual feedback, a paradigm known to involve mostly explicit re-aiming processes. Retention was tested 24 h later. Although there were no differences in day 1 acquisition between groups, individuals who experienced pain on day 1 demonstrated reduced retention on day 2. Furthermore, the degree of forgetting between days correlated with pain ratings during learning. In experiment 2, we examined the effects of a heat stimulus alone, which served as a control for (nonpainful) cutaneous stimulation, and found no effects on either acquisition or retention of learning. Thus, pain experienced during explicit, strategic locomotor learning interferes with motor memory consolidation processes and does so most likely through a pain mechanism and not an effect of distraction. These findings have important implications for understanding basic motor learning processes and for clinical rehabilitation, in which painful conditions are often treated through motor learning-based interventions.NEW & NOTEWORTHY Pain is a highly prevalent and burdensome experience that rehabilitation practitioners often treat using motor learning-based interventions. Here, we showed that experimental acute pain, but not a heat stimulus, during locomotor learning impaired 24-h retention of the newly learned walking pattern. The degree of retention loss was related to the perceived pain level during learning. These findings suggest important links between pain and motor learning that have significant implications for clinical rehabilitation.

Altered cognitive control network mediates the association between long-term pain and anxiety symptoms in primary dysmenorrhea

Neuroimaging studies have demonstrated the association of the cognitive control network (CCN) with the maintenance of chronic pain. However, whether and how dorsolateral prefrontal cortex (DLPFC), a key region within the CCN, is altered in menstrual pain is unclear. In this study, we aimed to investigate alterations in the DLPFC functional connectivity network in patients with primary dysmenorrhea (PDM). The study comprised 41 PDM patients and 39 matched healthy controls (HCs), all of whom underwent a resting-state functional MRI scan during the menstrual stage. All participants were instructed to complete the clinical assessment before the MRI scan. We used the DLPFC as the seed in resting-state functional connectivity (rsFC) analysis to investigate the difference between PDM patients and HCs. Compared to HCs, PDM patients showed increased right DLPFC rsFC at the bilateral lingual gyrus, dorsal anterior cingulate cortex (dACC), and middle cingulate cortex, and decreased left DLPFC rsFC at the right orbital frontal cortex. In addition, increased right DLPFC-bilateral dACC connectivity mediated the association between disease duration and the self-rating anxiety scale (SAS) scores in PDM patients. We confirmed that the DLPFC-dACC rsFC was associated with higher SAS scores, which could mediate the association between disease duration and anxiety symptoms in patients with PDM. Our findings provide central pathological evidence for an abnormal rsFC of the CCN in PDM patients, which may contribute to a better understanding of the neuropathophysiological mechanisms underlying PDM.

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.

Relation of gait measures with mild unilateral knee pain during walking using machine learning

Gait alterations in those with mild unilateral knee pain during walking may provide clues to modifiable alterations that affect progression of knee pain and osteoarthritis (OA). To examine this, we applied machine learning (ML) approaches to gait data from wearable sensors in a large observational knee OA cohort, the Multicenter Osteoarthritis (MOST) study. Participants completed a 20-m walk test wearing sensors on their trunk and ankles. Parameters describing spatiotemporal features of gait and symmetry, variability and complexity were extracted. We used an ensemble ML technique ("super learning") to identify gait variables in our cross-sectional data associated with the presence/absence of unilateral knee pain. We then used logistic regression to determine the association of selected gait variables with odds of mild knee pain. Of 2066 participants (mean age 63.6 [SD: 10.4] years, 56% female), 21.3% had mild unilateral pain while walking. Gait parameters selected in the ML process as influential included step regularity, sample entropy, gait speed, and amplitude dominant frequency, among others. In adjusted cross-sectional analyses, lower levels of step regularity (i.e., greater gait variability) and lower sample entropy(i.e., lower gait complexity) were associated with increased likelihood of unilateral mild pain while walking [aOR 0.80 (0.64-1.00) and aOR 0.79 (0.66-0.95), respectively].

Prediction and action in cortical pain processing

Predicting that a stimulus is painful facilitates action to avoid harm. But how distinct are the neural processes underlying the prediction of upcoming painful events vis-à-vis those taking action to avoid them? Here, we investigated brain activity as a function of current and predicted painful or nonpainful thermal stimulation, as well as the ability of voluntary action to affect the duration of upcoming stimulation. Participants performed a task which involved the administration of a painful or nonpainful stimulus (S1), which predicted an immediately subsequent very painful or nonpainful stimulus (S2). Pressing a response button within a specified time window during S1 either reduced or did not reduce the duration of the upcoming stimulation. Predicted pain increased activation in several regions, including anterior cingulate cortex (ACC), midcingulate cortex (MCC), and insula; however, activation in ACC and MCC depended on whether a meaningful action was performed, with MCC activation showing a direct relationship with motor output. Insula's responses for predicted pain were also modulated by potential action consequences, albeit without a direct relationship with motor output. These findings suggest that cortical pain processing is not specifically tied to the sensory stimulus, but instead, depends on the consequences of that stimulus for sensorimotor control of behavior.

Effect of Painful Electrical Stimuli on Readiness Potential in the Human Brain

The readiness potential (RP), which is a slow negative electrical brain potential that occurs before voluntary movement, can be interpreted as a measure of intrinsic brain activity originating from self-regulating mechanisms. Early and late components of the RP may indicate clinical-neurophysiological features such as motivation, preparation, intention, and initiation of voluntary movements. In the present study, we hypothesized that electrical pain stimuli modulate the preparatory brain activity for movement. The grand average evoked potentials were measured at sensory motor regions with EEG during an experimental protocol consisting of painful and nonpainful stimuli. Our results demonstrated that painful stimuli were preceded by an enhanced RP when compared to non-painful stimuli at the Cz channel (p < 0.05). Furthermore, the mean amplitude of the RP at the early phase was significantly higher for the painful stimuli when compared to the non-painful stimuli (p < 0.05). Our results indicate that electrical painful stimuli, which can be considered as an unpleasant and stressful condition, modulate the motor preparation at sensory motor regions to a different extent when compared to non-painful electrical stimuli. Since early component of the RP represents cortical activation due to anticipation of the stimuli and the allocation of attentional resources, our results suggest that painful stimuli may affect the motor preparation processes and the prediction of the movement at the cortical level.

Influence of acid-sensing ion channel blocker on behavioral responses in a zebrafish model of acute visceral pain

Acid-sensing ion channels (ASICs) play significant roles in numerous neurological and pathological conditions, including pain. Although acid-induced nociception has been characterized previously in zebrafish, the contribution of ASICs in modulating pain-like behaviors is still unknown. Here, we investigated the role of amiloride, a nonselective ASICs blocker, in the negative modulation of specific behavioral responses in a zebrafish-based model of acute visceral pain. We verified that intraperitoneal injection (i.p.) of 0.25, 0.5, 1.0, and 2.0 mg/mL amiloride alone or vehicle did not change zebrafish behavior compared to saline-treated fish. Administration of 2.5% acetic acid (i.p.) elicited writhing-like response evidenced by the abnormal body curvature and impaired locomotion and motor activity. Attenuation of acetic acid-induced pain was verified at lower amiloride doses (0.25 and 0.5 mg/mL) whereas 1.0 and 2.0 mg/mL abolished pain-like responses. The protective effect of the highest amiloride dose tested was evident in preventing writhing-like responses and impaired locomotion and vertical activity. Collectively, amiloride antagonized abdominal writhing-like phenotype and aberrant behaviors, supporting the involvement of ASICs in a zebrafish-based model of acute visceral pain.

Social Acts and Anticipation of Social Feedback

Socialization happens so regularly in humans that it can be perceived as an effortless activity. However, it reflects a sophisticated behavior, pervaded by anticipation and emotion. The fast-paced social interplay, strongly mediated by facial expressions, can be considered one of the most frequent high-order motor acts within the human behavioral repertoire. The ability to adequately process social feedback is critical for appropriate socialization and affects well-being. The social difficulties often observed in psychiatric patients highlight the link between mental health and successful socialization and the importance of characterizing the behavioral and neural mechanisms of social interaction. This chapter will present some cross-species evidence on the cortical regions engaged during social interactions including facial expressions, and the impact of induced or perceived social stress on the experience of social interactions.

Pain expectation and avoidance in the social context: an electrophysiological study

Contingent negative variation (CNV) is an informative electrophysiological measure of pain anticipation showing higher amplitudes when highly painful stimulation is expected while presenting lower amplitudes when low painful stimulation is expected. Two groups of participants were recruited: one group expected and received an electrical stimulation of different intensities while being alone in the room (i.e. without social context), while a second group performed the same experiment with an observer in the room (i.e. with social context). Lower pain ratings and slower reaction times were observed in the group with social context and these results were accompanied in this group by a lower amplitude in the early component of the CNV as well as a lower amplitude of the later component of the wave. These results show that CNV can be considered a precise measure of central elaboration of pain anticipation explaining both its perceptual and motor components.

The impact of experimental pain on shoulder movement during an arm elevated reaching task in a virtual reality environment

BACKGROUND

People with chronic shoulder pain have been shown to present with motor adaptations during arm movements. These adaptations may create abnormal physical stress on shoulder tendons and muscles. However, how and why these adaptations develop from the acute stage of pain is still not well-understood.

OBJECTIVE

To investigate motor adaptations following acute experimental shoulder pain during upper limb reaching.

METHODS

Forty participants were assigned to the Control or Pain group. They completed a task consisting of reaching targets in a virtual reality environment at three time points: (1) baseline (both groups pain-free), (2) experimental phase (Pain group experiencing acute shoulder pain induced by injecting hypertonic saline into subacromial space), and (3) Post experimental phase (both groups pain-free). Electromyographic (EMG) activity, kinematics, and performance data were collected.

RESULTS

The Pain group showed altered movement planning and execution as shown by a significant increased delay to reach muscles EMG peak and a loss of accuracy, compared to controls that have decreased their mean delay to reach muscles peak and improved their movement speed through the phases. The Pain group also showed protective kinematic adaptations using less shoulder elevation and elbow flexion, which persisted when they no longer felt the experimental pain.

CONCLUSION

Acute experimental pain altered movement planning and execution, which affected task performance. Kinematic data also suggest that such adaptations may persist over time, which could explain those observed in chronic pain populations.

The effects of long-term menstrual pain on pain empathy in women with primary dysmenorrhea

ABSTRACT

Primary dysmenorrhea (PDM) is not only a painful experience but also affects the psychological and affective states of women. Neuroimaging studies have revealed shared neural substrates for somatic and empathic pains in healthy subjects. However, little is known about the relationship between pain intensity and pain empathy in pain disorders. The cyclic nature of PDM makes it a unique model for investigating this issue during a patients' pain phase. To study how long-term pain modulates empathy for pain, T1-weighted magnetic resonance imaging scans were obtained in 39 PDM patients and 41 matched female healthy controls during menstruation. Subjects viewed static visual stimuli of the limbs submitted to painful and nonpainful stimulation to solicit empathy. The visual analogue scale for pain intensity and the Interpersonal Reactivity Index for empathic ability were also obtained. We found that women with PDM exhibited higher pain empathy compared with controls. The anterior insula and brain regions related to sensory discrimination with decreased gray matter volumes were not only shared but also acted as a mediator between pain intensity and pain empathy in PDM patients. In addition, the general linear modeling analysis revealed that long-term pain experience was a more important factor to pain empathy compared with pain intensity. This indicated that long-term pain may cause maladaptive brain structural plasticity, which may further affect psychological adjustment to bring patients more vivid pain when they witness suffering and distress in others.

Dispositional empathy predicts primary somatosensory cortex activity while receiving touch by a hand

Previous research revealed an active network of brain areas such as insula and anterior cingulate cortex when witnessing somebody else in pain and feeling empathy. But numerous studies also suggested a role of the somatosensory cortices for state and trait empathy. While recent studies highlight the role of the observer’s primary somatosensory cortex when seeing painful or nonpainful touch, the interaction of somatosensory cortex activity with empathy when receiving touch on the own body is unknown. The current study examines the relationship of touch related somatosensory cortex activity with dispositional empathy by employing an fMRI approach. Participants were touched on the palm of the hand either by the hand of an experimenter or by a rubber hand. We found that the BOLD responses in the primary somatosensory cortex were associated with empathy personality traits personal distress and perspective taking. This relationship was observed when participants were touched both with the experimenter’s real hand or a rubber hand. What is the reason for this link between touch perception and trait empathy? We argue that more empathic individuals may express stronger attention both to other’s human perceptions as well as to the own sensations. In this way, higher dispositional empathy levels might enhance tactile processing by top-down processes. We discuss possible implications of these findings.

Cortical dynamics of movement-evoked pain in chronic low back pain

KEY POINTS

Cortical activity underlying movement-evoked pain is not well understood, despite being a key symptom of chronic musculoskeletal pain. We combined high-density electroencephalography with a full-body reaching protocol in a virtual reality environment to assess cortical activity during movement-evoked pain in chronic low back pain. Movement-evoked pain in individuals with chronic low back pain was associated with longer reaction times, delayed peak velocity and greater movement variability. Movement-evoked pain was associated with attenuated disinhibition in prefrontal motor areas, as evidenced by an attenuated reduction in beta power in the premotor cortex and supplementary motor area.

ABSTRACT

Although experimental pain alters neural activity in the cortex, evidence of changes in neural activity in individuals with chronic low back pain (cLBP) remains scarce and results are inconsistent. One of the challenges in studying cLBP is that the clinical pain fluctuates over time and often changes during movement. The goal of the present study was to address this challenge by recording high-density electroencephalography (HD-EEG) data during a full-body reaching task to understand neural activity during movement-evoked pain. HD-EEG data were analysed using independent component analyses, source localization and measure projection analyses to compare neural oscillations between individuals with cLBP who experienced movement-evoked pain and pain-free controls. We report two novel findings. First, movement-evoked pain in individuals with cLBP was associated with longer reaction times, delayed peak velocity and greater movement variability. Second, movement-evoked pain was associated with an attenuated reduction in beta power in the premotor cortex and supplementary motor area. Our observations move the field forward by revealing attenuated disinhibition in prefrontal motor areas during movement-evoked pain in cLBP.

Mutation Carriers with Reduced C-Afferent Density Reveal Cortical Dynamics of Pain-Action Relationship during Acute Pain

The evidence that action shapes perception has become widely accepted, for example, in the domain of vision. However, the manner in which action-relevant factors might influence the neural dynamics of acute pain processing has remained underexplored, particularly the functional roles of anterior insula (AI) and midanterior cingulate cortex (mid-ACC), which are frequently implicated in acute pain. To address this, we examined a unique group of heterozygous carriers of the rare R221W mutation on the nerve growth factor (NGF) gene. R221W carriers show a congenitally reduced density of C-nociceptor afferent nerves in the periphery, but can nonetheless distinguish between painful and nonpainful stimulations. Despite this, carriers display a tendency to underreact to acute pain behaviorally, thus exposing a potential functional gap in the pain–action relationship and allowing closer investigation of how the brain integrates pain and action information. Heterozygous R221W carriers and matched controls performed a functional magnetic resonance imaging (fMRI) task designed to dissociate stimulus type (painful or innocuous) from current behavioral relevance (relevant or irrelevant), by instructing participants to either press or refrain from pressing a button during thermal stimulation. Carriers’ subjective pain thresholds did not differ from controls’, but the carrier group showed decreased task accuracy. Hemodynamic activation in AI covaried with task performance, revealing a functional role in pain–action integration with increased responses for task-relevant painful stimulation (“signal,” requiring button-press execution) over task-irrelevant stimulation (“noise,” requiring button-press suppression). As predicted, mid-ACC activation was associated with action execution regardless of pain. Functional connectivity between AI and mid-ACC increased as a function of reported urge to withdraw from the stimulus, suggesting a joint role for these regions in motivated action during pain. The carrier group showed greater activation of primary sensorimotor cortices—but not the AI and mid-ACC regions—during pain and action, suggesting compensatory processing. These findings indicate a critical role for the AI–mid-ACC axis in supporting a flexible, adaptive action selection during pain, alongside the accompanying subjective experience of an urge to escape the pain.

Hypervigilance for Bodily Sensations in the Back During a Movement Task in People With Chronic and Recurrent Low Back Pain

OBJECTIVES

The current study assessed the role of hypervigilance for bodily sensations in the back in long-term low back pain problems.

METHODS

People with chronic low back pain, recurrent low back pain, and no low back pain were compared on the extent to which they attended to somatosensory stimuli on the back during a movement task. To measure hypervigilance, somatosensory event-related potentials (SEPs) to task-irrelevant tactile stimuli on the back were measured when preparing movements in either a threatening or a neutral condition, indicated by a cue signaling possible pain on the back during movement or not.

RESULTS

Results showed stronger attending to stimuli on the back in the threat condition than in the neutral condition, as reflected by increased amplitude of the N96 SEP. However, this effect did not differ between groups. Similarly, for all 3 groups the amplitude of the P172 was larger for the threatening condition, suggesting a more general state of arousal resulting in increased somatosensory responsiveness. No significant associations were found between somatosensory attending to the back and theorized antecedents such as pain catastrophizing, pain-related fear, and pain vigilance.

DISCUSSION

The current study confirmed that individuals preparing a movement attended more toward somatosensory stimuli at the lower back when anticipating back pain during the movement, as measured by the N96 SEP. However, no differences were found between participants with chronic low back pain or recurrent low back pain, or the pain-free controls.

Reward and empathy in the treating clinician: the neural correlates of successful doctor-patient interactions

The goal of this study was to determine the neural correlates of successful doctor-patient interactions. We performed an experimental neuroimaging study where medical doctors (MDs) performed a treatment task while their brain activation pattern was measured, using functional magnetic resonance imaging (fMRI). MDs (25-37 years old) first performed a standardized clinical exam of a "professional patient". Unbeknownst to the doctors, the professional patient was a confederate that rated the doctors' clinical examination using the Consultation And Relational Empathy (CARE) questionnaire, a standardized protocol assessing a clinician's social interaction during a consultation. After the clinical exam, MDs were placed inside a brain scanner and the patient was placed on a chair next to the MD. MDs performed a treatment task where an analgesic device was used to alleviate the patient's pain (experimentally induced), while the MD's brain activity was measured with fMRI. MDs rated their own empathic concern (equivalent of compassion) and personal distress using the Interpersonal Reactivity Index questionnaire. The patient's rating of CARE was robustly related to the MD's own ratings of trait empathic concern and to compassion-related and reward-related activation of medial frontal brain regions during treatment. In contrast, there was no relation with MD's personal distress, nor with activation in regions associated with the aversive component of experiencing empathy. We conclude that a patient's positive experience of a medical examination is reflected in doctors' empathic concern and reward-related brain activations during treatment, suggesting that compassion and pleasure are key factors for successful doctor-patient interactions.

Somatosensory attending to the lower back is associated with response speed of movements signaling back pain

The present study investigated if preparing a movement that is expected to evoke pain results in hesitation to initiate the movement (i.e., avoidance) and, especially, if the allocation of attention to the threatened body part mediates such effect. To this end, healthy volunteers (N = 33) performed a postural perturbation task recruiting lower back muscles. In 'threat trials', the movement was sometimes followed by an experimental pain stimulus on the back, whereas in 'no-threat trials', a non-painful control stimulus was applied. Electroencephalography (EEG) was used to assess attending to the lower back. Specifically, somatosensory evoked potentials (SEPs) to task-irrelevant tactile stimuli administered to the lower back were recorded during movement preparation. Reaction times (RTs) were recorded to assess movement initiation. The results revealed faster responses and enhanced somatosensory attending to the lower back on threat trials than on no-threat trials. Importantly, the amplitude of the N95 SEP component predicted RTs and was found to partially mediate the effect of pain anticipation on movement initiation. These findings suggest that somatosensory attending might be a potential mechanism by which pain anticipation can modulate motor execution.

Pain Experience is Somatotopically Organized and Overlaps with Pain Anticipation in the Human Cerebellum

Many fMRI studies have shown activity in the cerebellum after peripheral nociceptive stimulation. We investigated whether the areas in the cerebellum that were activated after nociceptive thumb stimulation were separate from those after nociceptive toe stimulation. In an additional experiment, we investigated the same for the anticipation of a nociceptive stimulation on the thumb or toe. For his purpose, we used fMRI after an electrical stimulation of the thumb and toe in 19 adult healthy volunteers. Following nociceptive stimulation, different areas were activated by stimulation on the thumb (lobule VI ipsilaterally and Crus II mainly contralaterally) and toe (lobules VIII-IX and IV-V bilaterally and lobule VI contralaterally), i.e., were somatotopically organized. Cerebellar areas innervated non-somatotopically by both toe and thumb stimulation were the posterior vermis and Crus I, bilaterally. In the anticipation experiment, similar results were found. However, here, the somatotopically activated areas were relatively small for thumb and negligible for toe stimulation, while the largest area was innervated non-somatotopically and consisted mainly of Crus I and lobule VI bilaterally. These findings indicate that nociceptive stimulation and anticipation of nociceptive stimulation are at least partly processed by the same areas in the cerebellum. This was confirmed by an additional conjunction analysis. Based on our findings, we hypothesize that input that is organized in a somatotopical manner reflects direct input from the spinal cord, while non-somatotopically activated parts of the cerebellum receive their information indirectly through cortical and subcortical connections, possibly involved in processing contextual emotional states, like the expectation of pain.

Please empathize! Instructions to empathise strengthen response facilitation after pain observation

Recent research has shown that observing others in pain leads to a general facilitation of reaction times. The current study sheds further light on the relationship between pain observation and reaction time by exploring how bottom-up processes, in the form of perceived pain intensity, and top-down processes, in the form of explicit instructions to empathise, influence response facilitation after pain observation. Participants watched videos of a hand getting pierced by a needle or touched by a Q-tip. To manipulate bottom-up information, participants saw videos depicting either deep or shallow insertion of the needle. To investigate potential top-down modulation, half the participants were explicitly requested to empathise with the person in the video, while the other half were told to simply watch and attend to the video. Results from two experiments corroborate previous results showing response facilitation after pain observation. Critically, experiment 2 provides robust evidence that explicit instructions to empathise with a person in pain strengthen response facilitation. We discuss these results considering social cognitive neuroscience and experimental psychology studies of empathy and pain observation.

Motor Responses to Noxious Stimuli Shape Pain Perception in Chronic Pain Patients

Pain serves vital protective functions, which crucially depend on appropriate motor responses to noxious stimuli. Such responses not only depend on but can themselves shape the perception of pain. In chronic pain, perception is often decoupled from noxious stimuli and motor responses are no longer protective, which suggests that the relationships between noxious stimuli, pain perception, and behavior might be changed. We here performed a simple experiment to quantitatively assess the relationships between noxious stimuli, perception and behavior in 22 chronic pain patients and 22 age-matched healthy human participants. Brief noxious and tactile stimuli were applied to the participants’ hands and participants performed speeded motor responses and provided perceptual ratings of the stimuli. Multi-level moderated mediation analyses assessed the relationships between stimulus intensity, perceptual ratings and reaction times for both stimulus types. The results revealed a significantly stronger involvement of motor responses in the translation of noxious stimuli into perception than in the translation of tactile stimuli into perception. This significant influence of motor responses on pain perception was found for both chronic pain patients and healthy participants. Thus, stimulus-perception-behavior relationships appear to be at least partially preserved in chronic pain patients and motor-related as well as behavioral interventions might harness these functional relationships to modulate pain perception.

A meta-analytic study of experimental and chronic orofacial pain excluding headache disorders

Chronic orofacial pain (COFP) disorders are prevalent and debilitating pain conditions affecting the head, neck and face areas. Neuroimaging studies have reported functional and grey matter abnormalities, but not all the studies have reported consistent findings. Identifying convergent abnormalities across COFPs provides a basis for future hypothesis-driven research aimed at elucidating common CNS mechanisms. Here, we perform three coordinate-based meta-analyses according to PRISMA guidelines to elucidate the central mechanisms of orofacial pain disorders. Specifically, we investigated consistent patterns of: (1) brain function to experimental orofacial pain in healthy subjects, (2) structural and (3) functional brain abnormalities in COFP. We computed our coordinate-based meta-analyses using GingerALE. The experimental pain meta-analysis revealed increased brain activity in bilateral thalami, posterior mid-cingulate cortices, and secondary somatosensory cortices, the right posterior parietal cortex extending to the orofacial region of the right primary somatosensory cortex and the right insula, and decreased activity in the right somatomotor regions. The structural COFP meta-analysis identified consistent higher grey matter volume/concentration in the right ventral thalamus and posterior putamen of COFP patients compared to healthy controls. The functional COFP meta-analysis identified a consistent increase in brain activity in the left medial and posterior thalamus and lesser activity in the left posterior insula in COFP, compared to healthy controls. Overall, these findings provide evidence of brain abnormalities in pain-related regions, namely the thalamus and insula, across different COFP disorders. The convergence of thalamic abnormalities in both structure and function suggest a key role for this region in COFP pathophysiology.

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Identifying convergent abnormalities in COFP can elucidate novel therapeutic targets.

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Experimental orofacial pain is associated with activity in nociceptive processing brain areas.

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Chronic orofacial pain (COFP) is associated with abnormal thalamic activity and grey matter.

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Our review highlights the need for more high quality COFP brain imaging studies.

Designing Brains for Pain: Human to Mollusc

There is compelling evidence that the "what it feels like" subjective experience of sensory stimuli arises in the cerebral cortex in both humans as well as mammalian experimental animal models. Humans are alone in their ability to verbally communicate their experience of the external environment. In other species, sensory awareness is extrapolated on the basis of behavioral indicators. For instance, cephalopods have been claimed to be sentient on the basis of their complex behavior and anecdotal reports of human-like intelligence. We have interrogated the findings of avoidance learning behavioral paradigms and classical brain lesion studies and conclude that there is no evidence for cephalopods feeling pain. This analysis highlighted the questionable nature of anthropometric assumptions about sensory experience with increased phylogenetic distance from humans. We contend that understanding whether invertebrates such as molluscs are sentient should first begin with defining the computational processes and neural circuitries underpinning subjective awareness. Using fundamental design principles, we advance the notion that subjective awareness is dependent on observer neural networks (networks that in some sense introspect the neural processing generating neural representations of sensory stimuli). This introspective process allows the observer network to create an internal model that predicts the neural processing taking place in the network being surveyed. Predictions arising from the internal model form the basis of a rudimentary form of awareness. We develop an algorithm built on parallel observer networks that generates multiple levels of sensory awareness. A network of cortical regions in the human brain has the appropriate functional properties and neural interconnectivity that is consistent with the predicted circuitry of the algorithm generating pain awareness. By contrast, the cephalopod brain lacks the necessary neural circuitry to implement such an algorithm. In conclusion, we find no compelling behavioral, functional, or neuroanatomical evidence to indicate that cephalopods feel pain.

Semantically defined subdomains of functional neuroimaging literature and their corresponding brain regions

The functional neuroimaging literature has become increasingly complex and thus difficult to navigate. This complexity arises from the rate at which new studies are published and from the terminology that varies widely from study-to-study and even more so from discipline-to-discipline. One way to investigate and manage this problem is to build a "semantic space" that maps the different vocabulary used in functional neuroimaging literature. Such a semantic space will also help identify the primary research domains of neuroimaging and their most commonly reported brain regions. In this work, we analyzed the multivariate semantic structure of abstracts in Neurosynth and found that there are six primary domains of the functional neuroimaging literature, each with their own preferred reported brain regions. Our analyses also highlight possible semantic sources of reported brain regions within and across domains because some research topics (e.g., memory disorders, substance use disorder) use heterogeneous terminology. Furthermore, we highlight the growth and decline of the primary domains over time. Finally, we note that our techniques and results form the basis of a "recommendation engine" that could help readers better navigate the neuroimaging literature.

Effect of movement-related pain on behaviour and corticospinal excitability changes associated with arm movement preparation

KEY POINTS

Experimental pain or its anticipation influence motor preparation processes as well as upcoming movement execution, but the underlying physiological mechanisms remain unknown. Our results showed that movement-related pain modulates corticospinal excitability during motor preparation. In accordance with the pain adaptation theory, corticospinal excitability was higher when the muscle has an antagonist (vs. an agonist) role for the upcoming movement associated with pain. Anticipation of movement-related pain also affects motor initiation and execution, with slower movement initiation (longer reaction times) and faster movement execution compared to movements that do not evoke pain. These results confirm the implementation of protective strategies during motor preparation known to be relevant for acute pain, but which may potentially have detrimental long-term consequences and lead to the development of chronic pain.

ABSTRACT

When a movement repeatedly generates pain, we anticipate movement-related pain and establish self-protective strategies during motor preparation, but the underlying mechanisms remains poorly understood. The current study investigated the effect of movement-related pain anticipation on the modulation of behaviour and corticospinal excitability during the preparation of arm movements. Participants completed an instructed-delay reaction-time (RT) task consisting of elbow flexions and extensions instructed by visual cues. Nociceptive laser stimulations (unconditioned stimuli) were applied to the lateral epicondyle during movement execution in a specific direction (CS+) but not in the other (CS-), depending on experimental group. During motor preparation, transcranial magnetic stimulation was used to measure corticospinal excitability in the biceps brachii (BB). RT and peak end-point velocity were also measured. Neurophysiological results revealed an opposite modulation of corticospinal excitability in BB depending on whether it plays an agonist (i.e. flexion) or antagonist (i.e. extension) role for the CS+ movements (P < 0.001). Moreover, behavioural results showed that for the CS+ movements RT did not change relative to baseline, whereas the CS- movements were initiated more quickly (P = 0.023) and the CS+ flexion movements were faster relative to the CS- flexion movements (P < 0.001). This is consistent with the pain adaptation theory which proposes that in order to protect the body from further pain, agonist muscle activity is reduced and antagonist muscle activity is increased. If these strategies are initially relevant and lead to short-term pain alleviation, they may potentially have detrimental long-term consequences and lead to the development of chronic pain.

Empathy for pain motivates actions without altruistic effects: evidence of motor dynamics and brain activity

Empathy has been supposed to be a proximate mechanism of altruistic behavior. We investigated whether empathy for pain drives actions without altruistic effects and how such actions modulate neural responses to others’ pain. In two experiments, we asked healthy adults to press a button for no reason when viewing video clips showing faces with pain expressions receiving needle penetration or faces with neutral expressions receiving a cotton swab touch. Experiment 1 found that participants pressed a button with greater response force when watching painful than non-painful stimuli. Participants who reported greater unpleasant feelings pressed the button harder when viewing painful stimuli. Experiment 2 revealed that passively viewing painful vs non-painful stimuli increased blood-oxygen-level-dependent signals in the middle cingulate cortex, supplementary motor cortex, and bilateral second somatosensory and inferior frontal cortex, which, however, were reduced by the action of button press without altruistic effects. In addition, individuals who reported higher personal distress illustrated greater decrease of the second somatosensory activity induced by button press. Our results indicate that empathy for pain motivates simple actions without altruistic effects that in turn reduce neural responses to others’ pain, suggesting a functional role of action execution in self distress relief when viewing others’ suffering.

Observing painful events in others leads to a temporally extended general response facilitation in the self

Excitability in the motor cortex is modulated when we observe other people receiving a painful stimulus (Avenanti et al., Nat Neurosci 8(7):955-960, 2005). However, the task dependency of this modulation is not well understood, as different paradigms have yielded seemingly different results. Previous neurophysiological work employing transcranial magnetic stimulation (TMS) suggests that watching another person's hand being pierced by a needle leads to a muscle specific inhibition, assessed via motor evoked potentials. Results from previous behavioural studies suggest that overt behavioural responses are facilitated due to pain observation (Morrison et al., Cereb Cortex 17:2214-2222, 2007b; Morrison et al., Cognition 104:407-416, 2007a). There are several paradigmatic differences both between typical TMS studies and behavioural studies, and within behavioural studies themselves, that limit our overall understanding of how pain observation affects the motor system. In the current study, we combine elements of typical TMS experimental designs in a behavioural assessment of how pain observation affects overt behavioural responding. Specifically, we examined the muscle specificity, timing, and direction of modulation of motor responses due to pain observation. To assess muscle specificity, we employed pain and non-pain videos from previous TMS studies in a Go/No-Go task in which participants responded by either pressing a key with their index finger or with their foot. To assess timing, we examined response times for Go signals presented at 0 or 500 ms after the video. Results indicate that observation of another individual receiving a painful stimulus leads to a non-effector specific, temporally extended response facilitation (e.g., finger and foot facilitation present at 0 and 500 ms delays), compared to observation of non-pain videos. This behavioural facilitation effect differs from the typical motor inhibition seen in TMS studies, and we argue that the effects of pain observation on the motor system are state-dependent, with different states induced via task instructions. We discuss our results in light of previous work on motor responses to pain observation.

Influence of pain on motor preparation in the human brain

The protective function of pain depends on appropriate motor responses to avoid injury and promote recovery. The preparation and execution of motor responses is thus an essential part of pain. However, it is not yet fully understood how pain and motor processes interact in the brain. Here we used electroencephalography to investigate the effects of pain on motor preparation in the human brain. Twenty healthy human participants performed a motor task in which they performed button presses to stop increasingly painful thermal stimuli when they became intolerable. In another condition, participants performed button presses without concurrent stimulation. The results show that the amplitudes of preparatory event-related desynchronizations at alpha and beta frequencies did not differ between conditions. In contrast, the amplitude of the preparatory readiness potential was reduced when a button press was performed to stop a painful stimulus compared with a button press without concomitant pain. A control experiment with nonpainful thermal stimuli showed a similar reduction of the readiness potential when a button press was performed to stop a nonpainful thermal stimulus. Together, these findings indicate that painful and nonpainful thermal stimuli can similarly influence motor preparation in the human brain. Pain-specific effects on motor preparation in the human brain remain to be demonstrated.NEW & NOTEWORTHY Pain is inherently linked to motor processes, but the interactions between pain and motor processes in the human brain are not yet fully understood. Using electroencephalography, we show that pain reduces movement-preparatory brain activity. Further results indicate that this effect is not pain specific but independent of the modality of stimulation.

Pain-Related Suppression of Beta Oscillations Facilitates Voluntary Movement

Increased beta oscillations over sensorimotor cortex are antikinetic. Motor- and pain-related processes separately suppress beta oscillations over sensorimotor cortex leading to the prediction that ongoing pain should facilitate movement. In the current study, we used a paradigm in which voluntary movements were executed during an ongoing pain-eliciting stimulus to test the hypothesis that a pain-related suppression of beta oscillations would facilitate the initiation of a subsequent voluntary movement. Using kinematic measures, electromyography, and high-density electroencephalography, we demonstrate that ongoing pain leads to shorter reaction times without affecting the kinematics or accuracy of movement. Reaction time was positively correlated with beta power prior to movement in contralateral premotor areas. Our findings corroborate the view that beta-band oscillations are antikinetic and provide new evidence that pain primes the motor system for action. Our observations provide the first evidence that a pain-related suppression of beta oscillations over contralateral premotor areas leads to shorter reaction times for voluntary movement.

Measuring expectation of pain: Contingent negative variation in placebo and nocebo effects

BACKGROUND

Expectation is an important mechanism underlying placebo response. Here, we analysed expectation of placebo hypoalgesia and nocebo hyperalgesia by using, for the first time, the contingent negative variation (CNV), also known as expectancy wave.

METHODS

Subjects were presented a green or red cue followed by a train of either non painful or painful electrical stimuli, and expected hypoalgesia after the green and hyperalgesia after the red cue. In experiment 1, expectation was reinforced using a conditioning procedure whereby the green and red cues were paired with non painful and painful stimuli, respectively (acquisition). In a second session (test) the intensity of the stimuli was kept constant, regardless of cue. In experiment 2 no conditioning was performed and participants expected an altered pain perception indicated by the visual cues. CNV mean amplitude, time necessary to stop the train of stimuli (reaction time) and pain ratings were measured.

RESULTS

A difference in pain perception occurred when electrical stimuli followed the presentation of the green cue compared to the red in the test session, whereas reaction times showed no changes. The same difference occurred in the early CNV component, related to cognitive stimulus anticipation, whereas the late CNV component, related to motor preparation, did not change. Moreover, these differences in pain perception and CNV amplitude were less robust in the experiment 2.

CONCLUSION

Placebo hypoalgesia and nocebo hyperalgesia differently affect sensory (pain perception) and motor components (pain avoidance) of pain. Furthermore, CNV is an electrophysiological objective measure capable of dissecting these components.

SIGNIFICANCE

Dissection of placebo hypoalgesia, differentiating the sensory component (pain perception) from the motor component (pain avoidance). Study of these components using the contingent negative variation (CNV) as an electrophysiological objective measure.

How Accurate Appraisal of Behavioral Costs and Benefits Guides Adaptive Pain Coping

Coping with pain is a complex phenomenon encompassing a variety of behavioral responses and a large network of underlying neural circuits. Whether pain coping is adaptive or maladaptive depends on the type of pain (e.g., escapable or inescapable), personal factors (e.g., individual experiences with coping strategies in the past), and situational circumstances. Keeping these factors in mind, costs and benefits of different strategies have to be appraised and will guide behavioral decisions in the face of pain. In this review we present pain coping as an unconscious decision-making process during which accurately evaluated costs and benefits lead to adaptive pain coping behavior. We emphasize the importance of passive coping as an adaptive strategy when dealing with ongoing pain and thus go beyond the common view of passivity as a default state of helplessness. In combination with passive pain coping, we highlight the role of the reward system in reestablishing affective homeostasis and discuss existing evidence on a behavioral and neural level. We further present neural circuits involved in the decision-making process of pain coping when circumstances are ambiguous and, therefore, costs and benefits are difficult to anticipate. Finally, we address the wider implications of this topic by discussing its relevance for chronic pain patients.

The effect of acute pain on risky and intertemporal choice

Pain is a highly salient and attention-demanding experience that motivates people to act. We investigated the effect of pain on decision making by delivering acute thermal pain to participants' forearm while they made risky and intertemporal choices involving money. Participants (n = 107) were more risk seeking under pain than in a no-pain control condition when decisions involved gains but not when they involved equivalent losses. Pain also resulted in greater preference for immediate (smaller) over future (larger) monetary rewards. We interpret these results as a motivation to offset the aversive, pain-induced state, where monetary rewards become more appealing under pain than under no pain and when delivered sooner rather than later. Our findings add to the long-standing debate regarding the role of intuition and reflection in decision making.

Automated classification of pain perception using high-density electroencephalography data

The translation of brief, millisecond-long pain-eliciting stimuli to the subjective perception of pain is associated with changes in theta, alpha, beta, and gamma oscillations over sensorimotor cortex. However, when a pain-eliciting stimulus continues for minutes, regions beyond the sensorimotor cortex, such as the prefrontal cortex, are also engaged. Abnormalities in prefrontal cortex have been associated with chronic pain states, but conventional, millisecond-long EEG paradigms do not engage prefrontal regions. In the current study, we collected high-density EEG data during an experimental paradigm in which subjects experienced a 4-s, low- or high-intensity pain-eliciting stimulus. EEG data were analyzed using independent component analyses, EEG source localization analyses, and measure projection analyses. We report three novel findings. First, an increase in pain perception was associated with an increase in gamma and theta power in a cortical region that included medial prefrontal cortex. Second, a decrease in lower beta power was associated with an increase in pain perception in a cortical region that included the contralateral sensorimotor cortex. Third, we used machine learning for automated classification of EEG data into low- and high-pain classes. Theta and gamma power in the medial prefrontal region and lower beta power in the contralateral sensorimotor region served as features for classification. We found a leave-one-out cross-validation accuracy of 89.58%. The development of biological markers for pain states continues to gain traction in the literature, and our findings provide new information that advances this body of work.NEW & NOTEWORTHY The development of a biological marker for pain continues to gain traction in literature. Our findings show that high- and low-pain perception in human subjects can be classified with 89% accuracy using high-density EEG data from prefrontal cortex and contralateral sensorimotor cortex. Our approach represents a novel neurophysiological paradigm that advances the literature on biological markers for pain.

Pain and motor processing in the human cerebellum

Pain-related adaptations in movement require a network architecture that allows for integration across pain and motor circuits. Previous studies addressing this issue have focused on cortical areas such as the midcingulate cortex. Here, we focus on pain and motor processing in the human cerebellum. The goal of this study was to identify areas of activation in the cerebellum, which are common to pain and motor processing, and to determine whether the activation is limited to the superior and inferior cerebellar motor maps or extends into multimodal areas of the posterior cerebellum. Our observations identified overlapping activity in left and right lobules VI and VIIb during pain and motor processing. Activation in these multimodal regions persisted when pain and motor processes were combined within the same trial, and activation in contralateral left lobule VIIb persisted when stimulation was controlled for. Functional connectivity analyses revealed significant correlations in the BOLD time series between multimodal cerebellar regions and sensorimotor regions in the cerebrum including anterior midcingulate cortex, supplementary motor area, and thalamus. The current findings are the first to show multimodal processing in lobules VI and VIIb for motor control and pain processing and suggest that the posterior cerebellum may be important in understanding pain-related adaptations in motor control.

Functional Connectivity with the Default Mode Network Is Altered in Fibromyalgia Patients

Fibromyalgia syndrome (FMS) patients show altered connectivity with the network maintaining ongoing resting brain activity, known as the default mode network (DMN). The connectivity patterns of DMN with the rest of the brain in FMS patients are poorly understood. This study employed seed-based functional connectivity analysis to investigate resting-state functional connectivity with DMN structures in FMS. Sixteen female FMS patients and 15 age-matched, healthy control subjects underwent T2-weighted resting-state MRI scanning and functional connectivity analyses using DMN network seed regions. FMS patients demonstrated alterations to connectivity between DMN structures and anterior midcingulate cortex, right parahippocampal gyrus, left superior parietal lobule and left inferior temporal gyrus. Correlation analysis showed that reduced functional connectivity between the DMN and the right parahippocampal gyrus was associated with longer duration of symptoms in FMS patients, whereas augmented connectivity between the anterior midcingulate and posterior cingulate cortices was associated with tenderness and depression scores. Our findings demonstrate alterations to functional connectivity between DMN regions and a variety of regions which are important for pain, cognitive and emotional processing in FMS patients, and which may contribute to the development or maintenance of chronic symptoms in FMS.

Cerebellar direct current stimulation modulates pain perception in humans

PURPOSE

The cerebellum is involved in a wide number of integrative functions, but its role in pain experience and in the nociceptive information processing is poorly understood. In healthy volunteers we evaluated the effects of transcranial cerebellar direct current stimulation (tcDCS) by studying the changes in the perceptive threshold, pain intensity at given stimulation intensities (VAS:0-10) and laser evoked potentials (LEPs) variables (N1 and N2/P2 amplitudes and latencies).

METHODS

Fifteen subjects were studied before and after anodal, cathodal and sham tcDCS. LEPs were obtained using a neodymium:yttrium-aluminium-perovskite (Nd:YAP) laser and recorded from the dorsum of the left hand. VAS was evaluated by delivering laser pulses at two different intensities, respectively two and three times the perceptive threshold.

RESULTS

Cathodal polarization dampened significantly the perceptive threshold and increased the VAS score, while the anodal one had opposite effects. Cathodal tcDCS increased significantly the N1 and N2/P2 amplitudes and decreased their latencies, whereas anodal tcDCS elicited opposite effects. Motor thresholds assessed through transcranial magnetic stimulation were not affected by cerebellar stimulation.

CONCLUSIONS

tcDCS modulates pain perception and its cortical correlates. Since it is effective on both N1 and N2/P2 components, we speculate that the cerebellum engagement in pain processing modulates the activity of both somatosensory and cingulate cortices. Present findings prompt investigation of the cerebellar direct current polarization as a possible novel and safe therapeutic tool in chronic pain patients.

Top-Down Dysregulation-From ADHD to Emotional Instability

Deficient cognitive top-down executive control has long been hypothesized to underlie inattention and impulsivity in attention-deficit/hyperactivity disorder (ADHD). However, top-down cognitive dysfunction explains a modest proportion of the ADHD phenotype whereas the salience of emotional dysregulation is being noted increasingly. Together, these two types of dysfunction have the potential to account for more of the phenotypic variance in patients diagnosed with ADHD. We develop this idea and suggest that top-down dysregulation constitutes a gradient extending from mostly non-emotional top-down control processes (i.e., “cool” executive functions) to mainly emotional regulatory processes (including “hot” executive functions). While ADHD has been classically linked primarily to the former, conditions involving emotional instability such as borderline and antisocial personality disorder are closer to the other. In this model, emotional subtypes of ADHD are located at intermediate levels of this gradient. Neuroanatomically, gradations in “cool” processing appear to be related to prefrontal dysfunction involving dorsolateral prefrontal cortex (dlPFC) and caudal anterior cingulate cortex (cACC), while “hot” processing entails orbitofrontal cortex and rostral anterior cingulate cortex (rACC). A similar distinction between systems related to non-emotional and emotional processing appears to hold for the basal ganglia (BG) and the neuromodulatory effects of the dopamine system. Overall we suggest that these two systems could be divided according to whether they process non-emotional information related to the exteroceptive environment (associated with “cool” regulatory circuits) or emotional information related to the interoceptive environment (associated with “hot” regulatory circuits). We propose that this framework can integrate ADHD, emotional traits in ADHD, borderline and antisocial personality disorder into a related cluster of mental conditions.

Functional reorganisation in chronic pain and neural correlates of pain sensitisation: A coordinate based meta-analysis of 266 cutaneous pain fMRI studies

Maladaptive mechanisms of pain processing in chronic pain conditions (CP) are poorly understood. We used coordinate based meta-analysis of 266 fMRI pain studies to study functional brain reorganisation in CP and experimental models of hyperalgesia. The pattern of nociceptive brain activation was similar in CP, hyperalgesia and normalgesia in controls. However, elevated likelihood of activation was detected in the left putamen, left frontal gyrus and right insula in CP comparing stimuli of the most painful vs. other site. Meta-analysis of contrast maps showed no difference between CP, controls, mood conditions. In contrast, experimental hyperalgesia induced stronger activation in the bilateral insula, left cingulate and right frontal gyrus. Activation likelihood maps support a shared neural pain signature of cutaneous nociception in CP and controls. We also present a double dissociation between neural correlates of transient and persistent pain sensitisation with general increased activation intensity but unchanged pattern in experimental hyperalgesia and, by contrast, focally increased activation likelihood, but unchanged intensity, in CP when stimulated at the most painful body part.

ALE meta-analysis reveals dissociable networks for affective and discriminative aspects of touch

Emotionally-laden tactile stimulation-such as a caress on the skin or the feel of velvet-may represent a functionally distinct domain of touch, underpinned by specific cortical pathways. In order to determine whether, and to what extent, cortical functional neuroanatomy supports a distinction between affective and discriminative touch, an activation likelihood estimate (ALE) meta-analysis was performed. This meta-analysis statistically mapped reported functional magnetic resonance imaging (fMRI) activations from 17 published affective touch studies in which tactile stimulation was associated with positive subjective evaluation (n = 291, 34 experimental contrasts). A separate ALE meta-analysis mapped regions most likely to be activated by tactile stimulation during detection and discrimination tasks (n = 1,075, 91 experimental contrasts). These meta-analyses revealed dissociable regions for affective and discriminative touch, with posterior insula (PI) more likely to be activated for affective touch, and primary somatosensory cortices (SI) more likely to be activated for discriminative touch. Secondary somatosensory cortex had a high likelihood of engagement by both affective and discriminative touch. Further, meta-analytic connectivity (MCAM) analyses investigated network-level co-activation likelihoods independent of task or stimulus, across a range of domains and paradigms. Affective-related PI and discriminative-related SI regions co-activated with different networks, implicated in dissociable functions, but sharing somatosensory co-activations. Taken together, these meta-analytic findings suggest that affective and discriminative touch are dissociable both on the regional and network levels. However, their degree of shared activation likelihood in somatosensory cortices indicates that this dissociation reflects functional biases within tactile processing networks, rather than functionally and anatomically distinct pathways.

Altered sensorimotor activation patterns in idiopathic dystonia-an activation likelihood estimation meta-analysis of functional brain imaging studies

Dystonia is characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements or postures. Functional neuroimaging studies have yielded abnormal task‐related sensorimotor activation in dystonia, but the results appear to be rather variable across studies. Further, study size was usually small including different types of dystonia. Here we performed an activation likelihood estimation (ALE) meta‐analysis of functional neuroimaging studies in patients with primary dystonia to test for convergence of dystonia‐related alterations in task‐related activity across studies. Activation likelihood estimates were based on previously reported regional maxima of task‐related increases or decreases in dystonia patients compared to healthy controls. The meta‐analyses encompassed data from 179 patients with dystonia reported in 18 functional neuroimaging studies using a range of sensorimotor tasks. Patients with dystonia showed bilateral increases in task‐related activation in the parietal operculum and ventral postcentral gyrus as well as right middle temporal gyrus. Decreases in task‐related activation converged in left supplementary motor area and left postcentral gyrus, right superior temporal gyrus and dorsal midbrain. Apart from the midbrain cluster, all between‐group differences in task‐related activity were retrieved in a sub‐analysis including only the 14 studies on patients with focal dystonia. For focal dystonia, an additional cluster of increased sensorimotor activation emerged in the caudal cingulate motor zone. The results show that dystonia is consistently associated with abnormal somatosensory processing in the primary and secondary somatosensory cortex along with abnormal sensorimotor activation of mesial premotor and right lateral temporal cortex. Hum Brain Mapp 37:547–557, 2016. © 2015 Wiley Periodicals, Inc.

Psychosocial versus physiological stress - Meta-analyses on deactivations and activations of the neural correlates of stress reactions

Stress is present in everyday life in various forms and situations. Two stressors frequently investigated are physiological and psychosocial stress. Besides similar subjective and hormonal responses, it has been suggested that they also share common neural substrates. The current study used activation-likelihood-estimation meta-analysis to test this assumption by integrating results of previous neuroimaging studies on stress processing. Reported results are cluster-level FWE corrected. The inferior frontal gyrus (IFG) and the anterior insula (AI) were the only regions that demonstrated overlapping activation for both stressors. Analysis of physiological stress showed consistent activation of cognitive and affective components of pain processing such as the insula, striatum, or the middle cingulate cortex. Contrarily, analysis across psychosocial stress revealed consistent activation of the right superior temporal gyrus and deactivation of the striatum. Notably, parts of the striatum appeared to be functionally specified: the dorsal striatum was activated in physiological stress, whereas the ventral striatum was deactivated in psychosocial stress. Additional functional connectivity and decoding analyses further characterized this functional heterogeneity and revealed higher associations of the dorsal striatum with motor regions and of the ventral striatum with reward processing. Based on our meta-analytic approach, activation of the IFG and the AI seems to indicate a global neural stress reaction. While physiological stress activates a motoric fight-or-flight reaction, during psychosocial stress attention is shifted towards emotion regulation and goal-directed behavior, and reward processing is reduced. Our results show the significance of differentiating physiological and psychosocial stress in neural engagement. Furthermore, the assessment of deactivations in addition to activations in stress research is highly recommended.

Laser-Evoked Vertex Potentials Predict Defensive Motor Actions

The vertex potential is the largest response that can be recorded in the electroencephalogram of an awake, healthy human. It is elicited by sudden and intense stimuli, and is composed by a negative–positive deflection. The stimulus properties that determine the vertex potential amplitude have been well characterized. Nonetheless, its functional significance remains elusive. The dominant interpretation is that it reflects neural activities related to the detection of salient stimuli. However, given that threatening stimuli elicit both vertex potentials and defensive movements, we hypothesized that the vertex potential is related to the execution of defensive actions. Here, we directly compared the salience and motoric interpretations by investigating the relationship between the amplitude of laser-evoked potentials (LEPs) and the response time of movements with different defensive values. First, we show that a larger LEP negative wave (N2 wave) predicts faster motor response times. Second, this prediction is significantly stronger when the motor response is defensive in nature. Third, the relation between the N2 wave and motor response time depends not only on the kinematic form of the movement, but also on whether that kinematic form serves as a functional defense of the body. Therefore, the N2 wave of the LEP encodes key defensive reactions to threats.

The neural basis of the imitation drive

Spontaneous imitation is assumed to underlie the acquisition of important skills by infants, including language and social interaction. In this study, functional magnetic resonance imaging (fMRI) was used to examine the neural basis of ‘spontaneously’ driven imitation, which has not yet been fully investigated. Healthy participants were presented with movie clips of meaningless bimanual actions and instructed to observe and imitate them during an fMRI scan. The participants were subsequently shown the movie clips again and asked to evaluate the strength of their ‘urge to imitate’ (Urge) for each action. We searched for cortical areas where the degree of activation positively correlated with Urge scores; significant positive correlations were observed in the right supplementary motor area (SMA) and bilateral midcingulate cortex (MCC) under the imitation condition. These areas were not explained by explicit reasons for imitation or the kinematic characteristics of the actions. Previous studies performed in monkeys and humans have implicated the SMA and MCC/caudal cingulate zone in voluntary actions. This study also confirmed the functional connectivity between Urge and imitation performance using a psychophysiological interaction analysis. Thus, our findings reveal the critical neural components that underlie spontaneous imitation and provide possible reasons why infants imitate spontaneously.

Pain-Related Brain Activity Evoked by Active and Dynamic Arm Movement: Delayed-Onset Muscle Soreness as a Promising Model for Studying Movement-Related Pain in Humans

OBJECTIVE

To demonstrate delayed-onset muscle soreness (DOMS) is a suitable model for the study of movement-evoked pain, we attempted to identify brain regions specifically involved in pain evoked by active and dynamic movement under DOMS condition.

SUBJECT

Twelve healthy volunteers

METHODS

DOMS was induced in the left upper-arm flexor muscles by an eccentric elbow contraction exercise. Movement-evoked pain in the affected muscles was evaluated just before (day 0) and after (days 1-7 and 30) the exercise using a visual analog scale. Subjects underwent functional magnetic resonance imaging scans while performing repeated elbow flexion on day 2 (DOMS condition) and day 30 (painless condition). We compared brain activity between the DOMS and painless conditions.

RESULTS

Movement-evoked pain reached peak intensity on day 2 and disappeared by day 30 in all subjects. No subject felt pain at rest on either of these days. Contralateral primary motor cortex (M1), parietal operculum and bilateral presupplementary motor area (pre-SMA) showed greater activity during active and dynamic arm movement with DOMS than during the same movement without pain. There was no difference in activation of brain regions known collectively as the "pain matrix," except for the parietal operculum, between the two conditions.

CONCLUSION

Active and dynamic movement with pain selectively evoked activation of M1, pre-SMA, and parietal operculum, as assessed using DOMS. Our results demonstrate that DOMS is a promising experimental model for the study of movement-evoked pain in humans.

Mirroring pain in the brain: emotional expression versus motor imitation

Perception of pain in others via facial expressions has been shown to involve brain areas responsive to self-pain, biological motion, as well as both performed and observed motor actions. Here, we investigated the involvement of these different regions during emotional and motor mirroring of pain expressions using a two-task paradigm, and including both observation and execution of the expressions. BOLD responses were measured as subjects watched video clips showing different intensities of pain expression and, after a variable delay, either expressed the amount of pain they perceived in the clips (pain task), or imitated the facial movements (movement task). In the pain task condition, pain coding involved overlapping activation across observation and execution in the anterior cingulate cortex, supplementary motor area, inferior frontal gyrus/anterior insula, and the inferior parietal lobule, and a pain-related increase (pain vs. neutral) in the anterior cingulate cortex/supplementary motor area, the right inferior frontal gyrus, and the postcentral gyrus. The ‘mirroring’ response was stronger in the inferior frontal gyrus and middle temporal gyrus/superior temporal sulcus during the pain task, and stronger in the inferior parietal lobule in the movement task. These results strongly suggest that while motor mirroring may contribute to the perception of pain expressions in others, interpreting these expressions in terms of pain content draws more heavily on networks involved in the perception of affective meaning.