Bodily self-perception during voluntary actions: The causal contribution of premotor cortex and cerebellum

Body Ownership and the Motor System: Rapid Facilitation of Embodied Fake Hand Movement on Actual Movement Execution

Body ownership-the perception that one's body belongs to oneself-has been explored using a rubber hand illusion, in which individuals misperceive a fake hand as their own (i.e., embodiment of the fake hand) when an unseen real hand and a visible fake hand are stroked synchronously. Thus, the movement of an embodied fake body may be represented in one's own sensorimotor system. Using a combination of the rubber hand illusion and a motor task, we investigated whether simple movement of the embodied fake hand influenced the subsequent movement of the participants' hand. The participants lifted their own index finger immediately upon observing the index finger lifting on the embodied (rubber hand illusion) or non-embodied (non-rubber hand illusion) fake hand (Experiment 1), and a light-emitting diode turning on near the fake hand (Experiment 2). The reaction times, peak velocities, and peak acceleration were extracted from the participants' finger-lifting movements. In Experiment 1, the reaction time was significantly shorter in the rubber hand illusion condition than in the non-rubber hand illusion condition, suggesting the rapid facilitation effect of embodied fake hand movement on actual movement. However, no such motor facilitation was observed in Experiment 2, confirming that the improved reaction time in Experiment 1 resulted from the visual movement of the fake hand rather than attention to the fake hand itself. In contrast to the reaction time, the peak velocity and acceleration did not differ significantly in either experiment. These findings reflect the similar sensorimotor representations of illusory and actual self-movement.

Neurostimulation and Sense of Agency: Three tDCS Experiments on the Modulation of Intentional Binding

Objectives: This research investigated the impact of transcranial Direct Current Stimulation (tDCS) on sense of agency (SoA) when focusing on cortical regions like the cerebellum, the dorsolateral prefrontal cortex (DLPFC), and the angular gyrus (AG). To this aim, three experiments were carried out, and agency was assessed through the Wundt Clock Paradigm, which provides a measure of intentional binding. Methods: The first experiment provided offline cathodal stimulation applied to the right cerebellum, with the return electrode placed on the left DLPFC, and participants were randomly assigned to either the placebo group or the active group. The second experiment adopted the same montage as the previous one, but the online stimulation was provided in a within-subjects design. Results: Since none of these studies targeting the cerebellum produced significant results on the agency measures, we carried out a third experiment aimed to replicate a previous study that provided inhibitory stimulation of the left AG. However, this also showed no modulations of SoA. Conclusions: Several explanations could be given for these negative results. For example, the inter-individual variability, task complexity, and limitations of tDCS technology may contribute to the inconsistencies of the results. Also, the failure to replicate a previous study raises the issue of the replicability crisis in psychology. Nevertheless, this study may represent an important reference for research aimed at modulating SoA through the neuromodulation of brain areas included in the agency network. Future studies could benefit from assessing individual cognitive abilities supporting agency, optimizing stimulation protocols, and exploring alternative brain stimulation techniques to obtain significant results.

Neuromodulation of the Cerebellum for Motor Applications: A Systematic Review

BACKGROUND

Despite the connections and clear importance of the cerebellum in motor function, research utilizing cerebellar neuromodulation for treatment of movement disorders is still underdeveloped. Here we conduct a systematic review to investigate non-invasive neurostimulation of the cerebellum and its potential impact on motor systems and its function. Our aim is to give a general review of each neurostimulation study focusing on the cerebellum as a treatment target in the past five years at time of search, in order to update the field on current findings and inspire similar cerebellar neurostimulation research without unnecessary repetition.

METHODS

Using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, our search included articles over the past five years that evaluated neurostimulation of the cerebellum (e.g., transcranial magnetic stimulation, transcranial direct current stimulation, and transcranial alternating current stimulation, etc.). Inclusion criteria included: (1) neurostimulation (repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS)) of the cerebellum; (2) only original articles, and (3) outcomes focused on motor functions. Exclusion criteria included: (1) neurostimulation with the goal of targeting any brain structure other than the cerebellum and (2) reviews and conference abstracts.

RESULTS

The search revealed 82 distinct articles relevant to the research question. Included are 17 articles concerning rTMS, 56 articles concerning tDCS, and 9 articles concerning tACS. The majority of the studies are controlled trials of varying types, with 79, with two case studies and one pilot study.

CONCLUSIONS

Many studies showed significant effects on motor function and circuitry via non-invasive neurostimulation of the cerebellum. Common targets of cerebellar neurostimulation include visuomotor control, stroke rehabilitation for improvements in balance and coordination, and motor skill acquisition. The field is still exploring ideal parameters of neurostimulation for each disorder or function of interest. Future research areas should include the inclusion of individual anatomy, including functional connectivity, and improving stimulation selectivity.

Subcortical contributions to the sense of body ownership

The sense of body ownership (i.e. the feeling that our body or its parts belong to us) plays a key role in bodily self-consciousness and is believed to stem from multisensory integration. Experimental paradigms such as the rubber hand illusion have been developed to allow the controlled manipulation of body ownership in laboratory settings, providing effective tools for investigating malleability in the sense of body ownership and the boundaries that distinguish self from other. Neuroimaging studies of body ownership converge on the involvement of several cortical regions, including the premotor cortex and posterior parietal cortex. However, relatively less attention has been paid to subcortical structures that may also contribute to body ownership perception, such as the cerebellum and putamen. Here, on the basis of neuroimaging and neuropsychological observations, we provide an overview of relevant subcortical regions and consider their potential role in generating and maintaining a sense of ownership over the body. We also suggest novel avenues for future research targeting the role of subcortical regions in making sense of the body as our own.

Ego- and Geo-Centered References: A Functional Neuroimagery Study

INTRODUCTION

The integration of vestibular, visual, and somatosensory cues allows the perception of space through the orientation of our body and surrounding objects with respect to gravity. The main goal of this study was to identify the cortical networks recruited during the representation of body midline and the representation of verticality.

METHODS

Thirty right-handed healthy participants were evaluated using fMRI. Brain networks activated during a subjective straight-ahead (SSA) task were compared to those recruited during a subjective vertical (SV) task.

RESULTS

Different patterns of cortical activation were observed, with differential increases in the angular gyrus and left cerebellum posterior lobe during the SSA task, in right rolandic operculum and cerebellum anterior lobe during the SV task.

DISCUSSION

The activation of these areas involved in visuo-spatial functions suggests that bodily processes of great complexity are engaged in body representation and vertical perception. Interestingly, the common brain networks involved in SSA and SV tasks were comprised of areas of vestibular projection that receive multisensory information (parieto-occipital areas) and the cerebellum, and reveal a predominance of the right cerebral and cerebellar hemispheres. The outcomes of this first fMRI study designed to unmask common and specific neural mechanisms at work in gravity- or body-referenced tasks pave a new way for the exploration of spatial cognitive impairment in patients with vestibular or cortical disorders.

Premotor cortex is hypoactive during sustained vowel production in individuals with Parkinson's disease and hypophonia

Introduction

Hypophonia is a common feature of Parkinson's disease (PD); however, the contribution of motor cortical activity to reduced phonatory scaling in PD is still not clear.

Methods

In this study, we employed a sustained vowel production task during functional magnetic resonance imaging to compare brain activity between individuals with PD and hypophonia and an older healthy control (OHC) group.

Results

When comparing vowel production versus rest, the PD group showed fewer regions with significant BOLD activity compared to OHCs. Within the motor cortices, both OHC and PD groups showed bilateral activation of the laryngeal/phonatory area (LPA) of the primary motor cortex as well as activation of the supplementary motor area. The OHC group also recruited additional activity in the bilateral trunk motor area and right dorsal premotor cortex (PMd). A voxel-wise comparison of PD and HC groups showed that activity in right PMd was significantly lower in the PD group compared to OHC (p < 0.001, uncorrected). Right PMd activity was positively correlated with maximum phonation time in the PD group and negatively correlated with perceptual severity ratings of loudness and pitch.

Discussion

Our findings suggest that hypoactivation of PMd may be associated with abnormal phonatory control in PD.

Did you hear your action? An ecological approach to the senses of ownership and agency

The Sense of Ownership (SoO) and the Sense of Agency (SoA) are two key components of bodily self-consciousness. In this experiment, we investigated how they are affected by variations in the ecological validity of the moving Rubber Hand Illusion (mRHI) paradigm, which typically include three movement conditions: active congruent, passive congruent, and active incongruent. These conditions were either in a session in which no auditory feedback associated with finger-tapping was eliminated, or in a session in which such a feedback occurred. Since the presence of the auditory feedback more closely corresponds to what individuals experience in daily life when they tap their finger on a surface, sessions with feedback are more ecologically valid, and should thus result in a more marked SoO. Results indicated that in the active movement condition in which the illusion is typically found (congruent), the effect was enhanced when the feedback was present. This advantage emerged on both on objective and subjective measures of SoO. The SoA, on the other hand, is not affected by the auditory feedback.

Abnormal functional connectivity of the frontostriatal circuits in type 2 diabetes mellitus

Background

Type 2 diabetes mellitus (T2DM) is a metabolic disorder associated with an increased incidence of cognitive and emotional disorders. Previous studies have indicated that the frontostriatal circuits play a significant role in brain disorders. However, few studies have investigated functional connectivity (FC) abnormalities in the frontostriatal circuits in T2DM.

Objective

We aimed to investigate the abnormal functional connectivity (FC) of the frontostriatal circuits in patients with T2DM and to explore the relationship between abnormal FC and diabetes-related variables.

Methods

Twenty-seven patients with T2DM were selected as the patient group, and 27 healthy peoples were selected as the healthy controls (HCs). The two groups were matched for age and sex. In addition, all subjects underwent resting-state functional magnetic resonance imaging (rs-fMRI) and neuropsychological evaluation. Seed-based FC analyses were performed by placing six bilateral pairs of seeds within a priori defined subdivisions of the striatum. The functional connection strength of subdivisions of the striatum was compared between the two groups and correlated with each clinical variable.

Results

Patients with T2DM showed abnormalities in the FC of the frontostriatal circuits. Our findings show significantly reduced FC between the right caudate nucleus and left precentral gyrus (LPCG) in the patients with T2DM compared to the HCs. The FC between the prefrontal cortex (left inferior frontal gyrus, left frontal pole, right frontal pole, and right middle frontal gyrus) and the right caudate nucleus has a significant positive correlation with fasting blood glucose (FBG).

Conclusion

The results showed abnormal FC of the frontostriatal circuits in T2DM patients, which might provide a new direction to investigate the neuropathological mechanisms of T2DM.

Regenerative Virtual Therapy: The Use of Multisensory Technologies and Mindful Attention for Updating the Altered Representations of the Bodily Self

The term “regenerative medicine” (RM) indicates an emerging trend in biomedical sciences that aims at replacing, engineering, or regenerating human cells, tissues, or organs to restore or establish normal function. So far, the focus of RM has been the physical body. Neuroscience, however, is now suggesting that mental disorders can be broadly characterized by a dysfunction in the way the brain computes and integrates the representations of the inner and outer body across time [bodily self-consciousness (BSC)]. In this perspective, we proposed a new kind of clinical intervention, i.e., “Regenerative Virtual Therapy” (RVT), which integrates knowledge from different disciplines, from neuroscience to computational psychiatry, to regenerate a distorted or faulty BSC. The main goal of RVT was to use technology-based somatic modification techniques to restructure the maladaptive bodily representations behind a pathological condition. Specifically, starting from a Bayesian model of our BSC (i.e., body matrix), we suggested the use of mindful attention, cognitive reappraisal, and brain stimulation techniques merged with high-rewarding and novel synthetic multisensory bodily experience (i.e., a virtual reality full-body illusion in sync with a low predictabIlity interoceptive modulation) to rewrite a faulty experience of the body and to regenerate the wellbeing of an individual. The use of RVT will also offer an unprecedented experimental overview of the dynamics of our bodily representations, allowing the reverse-engineering of their functioning for hacking them using advanced technologies.