Agent-dependent modulation of corticospinal excitability during painful transcutaneous electrical stimulation

Aberrant Spontaneous Low-Frequency Brain Activity in Migraine: A Meta-Analysis of Resting-State fMRI Studies

BACKGROUND AND PURPOSE

Resting-state functional MRI has revealed abnormal brain activity in patients with migraine, though findings have been inconsistent. This meta-analysis utilized Seed-based d Mapping to assess variations in amplitude of low-frequency fluctuations (ALFF) and fractional amplitude of low-frequency fluctuations (fALFF). The aim was to identify common brain regions with altered spontaneous brain activity in migraine patients.

METHODS

A systematic search was conducted in PubMed, Web of Science, and Embase for studies published up to August 2023, comparing spontaneous low-frequency brain activity between migraine patients and healthy controls (HCs). Jackknife sensitivity, heterogeneity, publication bias, and meta-regression analyses were performed to ensure the robustness and reliability of our findings.

RESULTS

Nine studies, including 708 migraine patients and HCs, were included in the analysis. Applying a highly conservative family-wise error rate correction, no significant findings were observed. However, when a less conservative threshold was used, migraine patients exhibited increased ALFF/fALFF in the left anterior thalamus and the corticospinal tract but showed decreased values in the right middle frontal gyrus. Jackknife sensitivity analysis confirmed the reproducibility of these results, while heterogeneity analysis revealed significant variability across studies, likely due to differences in study design and patient populations.

CONCLUSIONS

This meta-analysis provides a comprehensive synthesis of neuroimaging evidence, linking migraine to abnormal spontaneous brain activity in regions associated with pain processing and nociceptive emotional modulation. These findings enhance our understanding of migraine pathophysiology and highlight potential targets for neuromodulation therapies, offering new directions for future research and clinical interventions.

The tangled threads: Unveiling the interplay between the sense of body ownership and the sense of agency in impacting the bodily-self representation in eating disorders

The feeling of owning a body (body ownership) and controlling its actions (sense of agency) contributes to the emergence of the bodily-self representation, whose alteration is at the root of the central psychopathology of Eating Disorders (EDs). Yet, studies addressing these aspects in EDs provided inconsistent results. Here, we simultaneously test body ownership and sense of agency in EDs compared to controls by exploiting different rubber hand illusion (RHI) paradigms (i.e., classic visuo-tactile, passive and active visuo-motor versions). In any RHI versions, no differences in the susceptibility to the illusion between EDs patients and controls emerged at the body ownership questionnaire, thus suggesting a normal multisensory integration mechanism. Crucially, correlation analysis revealed that a higher level of body dissatisfaction is associated with increased susceptibility to RHI, as measured by the body ownership questionnaire. Interestingly, patients with a bulimic variant of EDs reported agency toward the fake hand in the visuo-tactile RHI, revealing an abnormal sense of agency in absence of voluntary movement. Moreover, in the visuo-motor RHI, EDs patients exhibited a proprioceptive drift both in synchronous and asynchronous conditions. Hence, our results revealed a dissociation between explicit and implicit RHI measures, showing a more plastic bodily-self representation when the RHI enlists hand movements, leading to a stronger visual-capture of proprioception. This study contributes to understanding the intricate link between body ownership and agency, shedding light on the role of voluntary actions in driving the sense of self in EDs.

Topographic mapping of the sensorimotor qualities of empathic reactivity: A psychophysiological study in people with spinal cord injuries

The experience of empathy for pain is underpinned by sensorimotor and affective dimensions which, although interconnected, are at least in part behaviorally and neurally distinct. Spinal cord injuries (SCI) induce a massive, below-lesion level, sensorimotor body-brain disconnection. This condition may make it possible to test whether sensorimotor deprivation alters specific dimensions of empathic reactivity to observed pain. To explore this issue, we asked SCI people with paraplegia and healthy controls to observe videos of painful or neutral stimuli administered to a hand (intact) or a foot (deafferented). The stimuli were displayed by means of a virtual reality set-up and seen from a first person (1PP) or third person (3PP) visual perspective. A number of measures were recorded ranging from explicit behaviors like explicit verbal reports on the videos, to implicit measures of muscular activity (like EMG from the corrugator and zygomatic muscles that may represent a proxy of sensorimotor empathy) and of autonomic reactivity (like the electrodermal response and Respiratory Sinus Arrhythmia that may represent a general proxy of affective empathy). While no across group differences in explicit verbal reports about the pain stimuli were found, SCI people exhibited reduced facial muscle reactivity to the stimuli applied to the foot (but not the hand) seen from the 1PP. Tellingly, the corrugator activity correlated with SCI participants' neuropathic pain. There were no across group differences in autonomic reactivity suggesting that SCI lesions may affect sensorimotor dimensions connected to empathy for pain.

Abnormal sense of agency in eating disorders

The feeling of controlling one's own actions and, through them, impacting the external environment (i.e. Sense of Agency-SoA) can be relevant in the eating disorders (EDs) symptomatology. Yet, it has been poorly investigated. This study aims to implicitly assess SoA exploiting the Sensory Attenuation paradigm in two groups of EDs patients (Anorexia Nervosa Restrictive and Anorexia Nervosa Binge-Purging or Bulimia Nervosa) compared to a control group. We find that controls perceive self-generated stimuli as less intense than other-generated ones showing the classic pattern of sensory attenuation. By contrast, EDs patients show the opposite pattern, with self-generated perceived as more intense than other-generated stimuli. This result indicates an alteration of the implicit component of the feeling of control in EDs patients, thus suggesting a potential implication of these results for the clinical practice and the treatment of EDs symptomatology.

Spatial proximity to others induces plastic changes in the neural representation of the peripersonal space

Peripersonal space (PPS) is a highly plastic "invisible bubble" surrounding the body whose boundaries are mapped through multisensory integration. Yet, it is unclear how the spatial proximity to others alters PPS boundaries. Across five experiments (N = 80), by recording behavioral and electrophysiological responses to visuo-tactile stimuli, we demonstrate that the proximity to others induces plastic changes in the neural PPS representation. The spatial proximity to someone else's hand shrinks the portion of space within which multisensory responses occur, thus reducing the PPS boundaries. This suggests that PPS representation, built from bodily and multisensory signals, plastically adapts to the presence of conspecifics to define the self-other boundaries, so that what is usually coded as "my space" is recoded as "your space". When the space is shared with conspecifics, it seems adaptive to move the other-space away from the self-space to discriminate whether external events pertain to the self-body or to other-bodies.

Behavioural evidence of altered sensory attenuation in obesity

Body ownership (i.e., the conscious belief of owning a body) and sense of agency (i.e., being the agent of one's own movements) are part of a pre-reflective experience of bodily self, which grounds on low-level complex sensory-motor processes. Although previous literature had already investigated body ownership in obesity, sense of agency was never explored. Here, we exploited the sensory attenuation effect (i.e., an implicit marker of the sense of agency; SA effect) to investigate whether the sense of agency was altered in a sample of 18 individuals affected by obesity as compared with 18 healthy-weight individuals. In our experiment, participants were asked to rate the perceived intensity of self-generated and other-generated tactile stimuli. Healthy-weight individuals showed a significantly greater SA effect than participants affected by obesity. Indeed, while healthy-weight participants perceived self-generated stimuli as significantly less intense as compared to externally generated ones, this difference between stimuli was not reported by affected participants. Our results relative to the SA effect pinpointed an altered sense of agency in obesity. We discussed this finding within the motor control framework with reference to obesity. We encouraged future research to further explore such effect and its role in shaping the clinical features of obesity.

Pain, No Gain: Acute Pain Interrupts Motor Imagery Processes and Affects Mental Training-Induced Plasticity

Pain influences both motor behavior and neuroplastic adaptations induced by physical training. Motor imagery (MI) is a promising method to recover motor functions, for instance in clinical populations with limited endurance or concomitant pain. However, the influence of pain on the MI processes is not well established. This study investigated whether acute experimental pain could modulate corticospinal excitability assessed at rest and during MI (Exp. 1) and limit the use-dependent plasticity induced by MI practice (Exp. 2). Participants imagined thumb movements without pain or with painful electrical stimulations applied either on digit V or over the knee. We used transcranial magnetic stimulation to measure corticospinal excitability at rest and during MI (Exp. 1) and to evoke involuntary thumb movements before and after MI practice (Exp. 2). Regardless of its location, pain prevented the increase of corticospinal excitability that is classically observed during MI. In addition, pain blocked use-dependent plasticity following MI practice, as testified by a lack of significant posttraining deviations. These findings suggest that pain interferes with MI processes, preventing the corticospinal excitability facilitation needed to induce use-dependent plasticity. Pain should be carefully considered for rehabilitation programs using MI to restore motor function.

Immersive virtual reality reveals that visuo-proprioceptive discrepancy enlarges the hand-centred peripersonal space

Vision and proprioception, informing the system about the body position in space, seem crucial in defining the boundary of the peripersonal space (PPS). What happens to the PPS representation when a conflict between vision and proprioception arises? We capitalize on the Immersive Virtual Reality to dissociate vision and proprioception by presenting the participants' 3D hand image in congruent/incongruent positions with respect to the participants' real hand. To measure the hand-centred PPS, we exploit multisensory integration occurring when visual stimuli are delivered simultaneously with tactile stimuli applied to a body district; i.e., visual enhancement of touch (VET). Participants are instructed to respond to tactile stimuli while ignoring visual stimuli (red LED), which can appear either near to or far from the hand receiving tactile (electrical) stimuli. The results show that, when vision and proprioception are congruent (i.e., real and virtual hand coincide), a space-dependent modulation of the VET effect occurs (with faster responses when visual stimuli are near to than far from the stimulated hand). Contrarily, when vision and proprioception are incongruent (i.e., a discrepancy between real and virtual hand is present), a comparable VET effect is observed when visual stimuli occur near to the real hand and when they occur far from it, but close to the virtual hand. These findings, also confirmed by the independent estimate of a Bayesian Causal Inference model, suggest that, when the visuo-proprioceptive discrepancy makes the coding of the hand position less precise, the hand-centred PPS is enlarged, likely to optimize reactions to external events.

Self-Harming and Sense of Agency in Patients With Borderline Personality Disorder

Self-harm is considered a pervasive problem in several psychopathologies, and especially in Borderline Personality Disorder (BPD). Self-harming behaviors may be enacted for many purposes for example to regulate emotions and to reduce dissociation. BPD patients often report dissociative episodes, which may be related to an altered body awareness, and in particular to an altered awareness of the sense of agency. The sense of agency draws in part upon perceptions of being in control of our bodies and our physical movements, of being able to act upon environments. In this study, we aim to investigate whether dissociative experiences of BPD patients may be linked to an altered sense of agency and whether self-injurious actions may, through strong sensorial stimulation, constitute a coping strategy for the reduction of the distress associated with these dissociative experiences. A group of 20 BPD patients, of whom 9 presented self-harming behaviors, took part in the study and were compared with an age-matched control group of 20 healthy individuals. Sense of agency was evaluated through the Sensory Attenuation paradigm. In this paradigm, in a comparison with externally generated sensations, the degree to which perceived intensity of self-generated sensations is reduced is considered an implicit measure of sense of agency. As we expected, we found a significant difference in the perceptions of the two groups. The attenuation effect appeared to be absent in the BPD group while it was present in the control group. However, further analysis revealed that those BPD patients who engaged in self-harming behaviors presented a degree of attenuation which was similar to that of the control group. These results confirm the hypothesis that self-injurious actions constitute a coping strategy for increasing the sense of agency. We finally discuss the correlation of these experimental results with some clinical self-evaluation measures assessing dissociation, anxiety, depression, and affective dysregulation.