Synchronous Stimulation Research Articles

Evaluation of a New Mobile Virtual Reality Setup to Alter Pain Perception: Pilot Development and Usability Study in Healthy Participants.

Chronic pain presents a significant treatment challenge, often leading to frustration for both patients and therapists due to the limitations of traditional methods. Research has shown that synchronous visuo-tactile stimulation, as used in the rubber hand experiment, can induce a sense of ownership over a fake body part and reduces pain perception when ownership of the fake body part is reported. The effect of the rubber hand experiment can be extended to the full body, for example, during the full-body illusion, using both visuo-tactile and cardiovisual signals. This study first aimed to evaluate the usability and accuracy of a novel, mobile virtual reality (VR) setup that displays participants' heartbeats as a flashing silhouette on a virtual avatar, a technique known as the cardiovisual full-body illusion. The second part of the study investigated the effects of synchronous cardiovisual stimulation on pain perception and ownership in 20 healthy participants as compared with asynchronous stimulation (control condition). The setup comprised a head-mounted display (HMD) and a heart rate measurement device. A smartphone-based HMD (Samsung Galaxy S8+) was selected for its mobility, and heart rates were measured using smartwatches with photoplethysmography (PPG). The accuracy of 2 smartwatch positions was compared with a 5-point electrocardiogram (ECG) standard in terms of their accuracy (number and percent of missed beats). Each participant underwent two 5-minute sessions of synchronous cardiovisual stimulation and two 5-minute sessions of asynchronous cardiovisual stimulation (total of 4 sessions), followed by pain assessments. Usability, symptoms of cybersickness, and ownership of the virtual body were measured using established questionnaires (System Usability Scale, Simulator Sickness Questionnaire, Ownership Questionnaire). Pain perception was assessed using advanced algometric methods (Algopeg and Somedic algometer). Results demonstrated high usability scores (mean 4.42, SD 0.56; out of 5), indicating ease of use and acceptance, with minimal side effects (mean 1.18, SD 0.46; out of a possible 4 points on the Simulator Sickness Questionnaire). The PPG device showed high heart rate measurement precision, which improved with optimized filtering and peak detection algorithms. However, compared with previous work, no significant effects on body ownership and pain perception were observed between the synchronous and asynchronous conditions. These findings are discussed in the context of existing literature on VR interventions for chronic pain. In conclusion, while the new VR setup showed high usability and minimal side effects, it did not significantly affect ownership or pain perception. This highlights the need for further research to refine VR-based interventions for chronic pain management, considering factors like visual realism and perspective.

Associative plasticity of granule cell inputs to cerebellar Purkinje cells.

Granule cells of the cerebellum make up to 175,000 excitatory synapses on a single Purkinje cell, encoding the wide variety of information from the mossy fibre inputs into the cerebellar cortex. The granule cell axon is made of an ascending portion and a long parallel fibre extending at right angles, an architecture suggesting that synapses formed by the two segments of the axon could encode different information. There are controversial indications that ascending axon (AA) and parallel fibre (PF) synapse properties and modalities of plasticity are different. We tested the hypothesis that AA and PF synapses encode different information, and that the association of these distinct inputs to Purkinje cells might be relevant to the circuit and trigger plasticity, similar to the coincident activation of PF and climbing fibre inputs. Here, by recording synaptic currents in Purkinje cells from either proximal or distal granule cells (mostly AA and PF synapses, respectively), we describe a new form of associative plasticity between these two distinct granule cell inputs. We show for the first time that synchronous AA and PF repetitive train stimulation, with inhibition intact, triggers long-term potentiation (LTP) at AA synapses specifically. Furthermore, the timing of the presentation of the two inputs controls the outcome of plasticity and induction requires NMDAR and mGluR1 activation. The long length of the PFs allows us to preferentially activate the two inputs independently, and despite a lack of morphological reconstruction of the connections, these observations reinforce the suggestion that AA and PF synapses have different coding capabilities and plasticity that is associative, enabling effective association of information transmitted via granule cells.

Impact of minimal self disorders on naturalistic episodic memory in first-episode psychosis and parallels in healthy individuals with schizotypal traits.

Self-disorders constitute a core feature of the schizophrenia spectrum, including early stages such as first-episode psychosis (FEP). These disorders impact the minimal Self, or bodily self-consciousness, which refers to the basic, pre-reflective sense of embodied experience. The minimal Self is intrinsically linked to episodic memory, which captures specific past experiences of the Self. However, research on this relationship in the schizophrenia spectrum remains scarce. This pilot study aimed to investigate how the minimal Self modulated episodic memory of naturalistic events in FEP, using immersive virtual reality. A secondary objective was to examine the relationships between sense of Self, embodiment, episodic memory, schizotypal personality traits in healthy participants (CTL), and psychopathology in FEP. A full-body illusion was induced in 10 FEP and 35 matched CTL, using a first-person avatar, with synchronous or asynchronous visuomotor stimulation (strong or weak embodiment conditions, respectively). Following embodiment induction, participants navigated a virtual city and encountered naturalistic daily life events, which were incidentally encoded. Episodic memory of these events was assessed through a comprehensive recognition task (factual and contextual information, retrieval phenomenology). Sense of Self, schizotypal personality traits, and psychopathology were assessed via self-reported questionnaires or clinical assessments. Synchronous visuomotor stimulation successfully induced a stronger sense of embodiment in both FEP and CTL. The strong embodiment condition was associated with reduced perceived virtual space occupation by the body in FEP. Under strong embodiment, FEP performed significantly worse than CTL in contextual information recognition, but their ratings for retrieval phenomenology were comparable to CTL. Conversely, under weak embodiment, FEP performed similarly to CTL in contextual information recognition, but they rated retrieval phenomenology significantly lower. For CTL, we observed a slight, though non-significant, enhancement in recognition memory under strong compared to weak embodiment. Additionally, higher schizotypy in CTL correlated with a diminished sense of Self and poorer episodic memory. Disturbances in the minimal Self in FEP are associated with episodic memory impairments. These findings emphasise the importance of targeting minimal Self-disorders in schizophrenia spectrum disorders, since episodic memory impairments may negatively affect patients' quality of life and psychosocial outcomes. Additionally, they support a fully dimensional model of schizotypy.

Amelioration of Focal Hand Dystonia via Low-Frequency Repetitive Somatosensory Stimulation.

Dystonia presents a growing concern based on evolving prevalence insights. Previous research found that, in cervical dystonia, high-frequency repetitive somatosensory stimulation (RSS; HF-RSS) applied on digital nerves paradoxically diminishes sensorimotor inhibitory mechanisms, whereas low-frequency RSS (LF-RSS) increases them. However, direct testing on affected body parts was not conducted. This study aims to investigate whether RSS applied directly to forearm muscles involved in focal hand dystonia can modulate cortical inhibitory mechanisms and clinical symptoms. We applied HF-RSS and LF-RSS, the latter either synchronously or asynchronously, on forearm muscles involved in dystonia. Outcome measures included paired-pulse somatosensory evoked potentials, spatial lateral inhibition measured by double-pulse somatosensory evoked potentials, short intracortical inhibition tested with transcranial magnetic stimulation, electromyographic activity from dystonic muscles, and behavioral measures of hand function. Both synchronous and asynchronous low-frequency somatosensory stimulation improved cortical inhibitory interactions, indicated by increased short intracortical inhibition and lateral spatial inhibition, as well as decreased amplitude of paired-pulse somatosensory evoked potentials. Opposite effects were observed with high-frequency stimulation. Changes in electrophysiological markers were paralleled by behavioral outcomes: although low-frequency stimulations improved hand function tests and reduced activation of dystonic muscles, high-frequency stimulation operated in an opposite direction. Our findings confirm the presence of abnormal homeostatic plasticity in response to RSS in the sensorimotor system of patients with dystonia, specifically in inhibitory circuits. Importantly, this aberrant response can be harnessed for therapeutic purposes through the application of low-frequency electrical stimulation directly over dystonic muscles. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Malleability of the sense of bodily self in early childhood: 5- and 6-year-old children show the enfacement illusion

The mechanisms underlying the developing sense of bodily self are debated. Whereas some scholars stress the role of sensory factors, others propose the importance of contextual factors. By manipulating multisensory stimulation and social familiarity with the other person, we explored two factors that are proposed to relate to young children’s developing sense of bodily self. Including an adult sample allowed us to investigate age-related differences of the malleability of the bodily self. To this end, the study implemented an enfacement illusion with children (N = 64) and adults (N = 33). Participants were exposed to one trial with synchronous interpersonal multisensory stimulation and one trial with asynchronous interpersonal multisensory stimulation—either with a stranger or with the mother as the other person. A self-recognition task using morph videos of self and other and an enfacement questionnaire were implemented as dependent measures. Results revealed evidence for the presence of the enfacement effect in children in both measures. The identity of the other person had a significant effect on the self-recognition task. Contrary to our hypothesis, the effect was significantly smaller in the caregiver condition. No significant differences between children and adults emerged. Our results demonstrate the role of both multisensory stimulation and contextual—here social familiarity—factors for the construction and development of a bodily self. The study provides developmental science with a novel approach to the bodily self by showing the validity of the self-recognition task in a child sample. Overall, the study supports proposals that the sense of bodily self is malleable early in development.

Enhancing bodily self-consciousness in the virtual world with synchronous multisensory stimulation, interoceptive feedback and peripersonal space expansion: A narrative review

The article explores the link between neuroscience and the design fields by discussing works on predictive brain, conscious mind, perception, and peripersonal space to increase bodily self-consciousness in the virtual world. Unlike the physical reality, the virtual world often lacks the intricate bodily feedback necessary for self-consciousness, thus resulting in less complete virtual representations. By incorporating findings from neuroscience and the virtual world, this research suggests a theoretical approach to enhance bodily self-consciousness in different virtual worlds, particularly augmented or diminished mixed realities and holistic virtual reality. This is achieved through synchronous multisensory stimulation (visuo-tactile), interoceptive feedback, and peripersonal space expansion (visuo-tactile and audio–tactile). As a narrative review, the article not only suggests a theoretical method but also highlights the potential for future practical experiments to apply these insights.

Experiencing an Elongated Limb in Virtual Reality Modifies the Tactile Distance Perception of the Corresponding Real Limb.

In measurement, a reference frame is needed to compare the measured object to something already known. This raises the neuroscientific question of which reference frame is used by humans when exploring the environment. Previous studies suggested that, in touch, the body employed as measuring tool also serves as reference frame. Indeed, an artificial modification of the perceived dimensions of the body changes the tactile perception of external object dimensions. However, it is unknown if such a change in tactile perception would occur when the body schema is modified through the illusion of owning a limb altered in size. Therefore, employing a virtual hand illusion paradigm with an elongated forearm of different lengths, we systematically tested the subjective perception of distance between two points [tactile distance perception (TDP) task] on the corresponding real forearm following the illusion. Thus, the TDP task is used as a proxy to gauge changes in the body schema. Embodiment of the virtual arm was found significantly greater after the synchronous visuotactile stimulation condition compared with the asynchronous one, and the forearm elongation significantly increased the TDP. However, we did not find any link between the visuotactile-induced ownership over the elongated arm and TDP variation, suggesting that vision plays the main role in the modification of the body schema. Additionally, significant effect of elongation found on TDP but not on proprioception suggests that these are affected differently by body schema modifications. These findings confirm the body schema malleability and its role as a reference frame in touch.

Evaluation of physiological response and synchronisation errors during synchronous and pseudosynchronous stimulation trials

Rhythm perception and synchronisation is musical ability with neural basis defined as the ability to perceive rhythm in music and synchronise body movements with it. The study aimed to check the errors of synchronisation and physiological response as a reaction of the subjects to metrorhythmic stimuli of synchronous and pseudosynchronous stimulation (synchronisation with an externally controlled rhythm, but in reality controlled or produced tone by tapping) Nineteen subjects without diagnosed motor disorders participated in the study. Two tests were performed, where the electromyography signal and reaction time were recorded using the NORAXON system. In addition, physiological signals such as electrodermal activity and blood volume pulse were measured using the Empatica E4. Study 1 consisted of adapting the finger tapping test in pseudosynchrony with a given metrorhythmic stimulus with a selection of preferred, choices of decreasing and increasing tempo. Study 2 consisted of metrorhythmic synchronisation during the heel stomping test. Numerous correlations and statistically significant parameters were found between the response of the subjects with respect to their musical education, musical and sports activities. Most of the differentiating characteristics shown evidence of some group division in the undertaking of musical activities. The use of detailed analyses of synchronisation errors can contribute to the development of methods to improve the rehabilitation process of subjects with motor dysfunction, and this will contribute to the development of an expert system that considers personalised musical preferences.

The efficacy and safety of bilateral synchronous transcutaneous auricular vagus nerve stimulation for prolonged disorders of consciousness: a multicenter, double-blind, stratified, randomized controlled trial protocol.

Treatment of disorders of consciousness (DOC) poses a huge challenge for clinical medicine. Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive neuromodulation method, which shows potential in improving recovery of DOC. However, the evidence came from single-center, small-sample randomized controlled trial, which is insufficient to form a conclusion. Thereby, we propose a prospective, multicenter, double-blind, stratified, two-arm randomized controlled trial protocol to investigate the efficacy and safety of bilateral synchronous taVNS for treatment of DOC. We aim to recruit 382 patients with prolonged DOC, and divide them into an active stimulation group and a sham stimulation group. The patients in the active stimulation group will receive bilateral synchronous taVNS with a 200 μs pulse width, 20 Hz frequency, and personal adjusted intensity. The sham stimulation group will wear the same stimulator but without current output. Both groups will receive treatment for 30 min per session, twice per day, 6 days per week lasting for 4 weeks. The clinical assessment including Coma Recovery Scale-Revised (CRS-R), Full Outline of Unresponsiveness (FOUR), Glasgow Coma Scale (GCS), and Extended Glasgow Outcome Scale (GOS-E) will be conducted to evaluate its efficacy. Heart rate variability (HRV), blood pressure, and adverse events will be recorded to evaluate its safety. These results will enable us to investigate the efficacy and safety of taVNS for DOC. This protocol will provide multicenter, large-sample, high-quality Class II evidence to support bilateral synchronous taVNS for DOC, and will advance the field of treatment options for DOC.Clinical trial registration:https://www.chictr.org.cn/showproj.html?proj=221851, ChiCTR2400081978.

Stimulus intensity and temporal configuration interact during bimodal learning and memory in honey bees.

Multimodal integration is a core neural process with a keen relevance during ecological tasks requiring learning and memory, such as foraging. The benefits of learning multimodal signals imply solving whether the components come from a single event. This challenge presumably depends on the timing and intensity of the stimuli. Here, we used simultaneous and alternate presentations of olfactory and visual stimuli, at low and high intensities, to understand how temporal and intensity variations affect the learning of a bimodal stimulus and its components. We relied on the conditioning of the proboscis extension response (PER) to train honey bees to an appetitive learning task with bimodal stimuli precisely controlled. We trained bees to stimuli with different synchronicity and intensity levels. We found that synchronicity, order of presentation, and intensity significantly impacted the probability of exhibiting conditioned PER responses and the latency of the conditioned responses. At low intensities, synchronous bimodal inputs produced maximal multisensory enhancement, while asynchronous temporal orders led to lower performances. At high intensities, the relative advantage of the synchronous stimulation diminished, and asynchronous stimuli produced similar performances. Memory retention was higher for the olfactory component and bimodal stimuli compared to the visual component, irrespective of the training's temporal configuration. Bees retained the asynchronous bimodal configuration to a lesser extent than the synchronous one, depending on the stimulus intensity. We conclude that time (synchrony), order of presentation, and intensity have interdependent effects on bee learning and memory performance. This suggests caution when assessing the independent effects of each factor.

Prevalence of Adrenal Insufficiency in Korean Patients undergoing Total Knee Arthroplasty.

This study investigated the prevalence of adrenal insufficiency among patients admitted for total knee arthroplasty (TKA) due to osteoarthritis and identified factors contributing to adrenal insufficiency. We divided the patients into two groups based on the results of preoperative standard-dose short synchronous stimulation tests: group 1 (adrenal insufficiency) and group 2 (normal adrenal function). We also assessed the prevalence of adrenal insufficiency and compared the numbers of patients who received oral steroids, the frequency of previous steroid injection use, and the frequency of systemic symptoms of steroid depletion such as fatigue and loss of appetite between the two groups. Multiple regression analysis was performed to identify factors related to adrenal insufficiency. The prevalence of adrenal insufficiency was 60.0% (120/200). Group 1 had higher numbers of previous steroid injections (12.8±10.2 vs. 6.8±7.9) and patients taking oral steroids (18/120 vs. 3/80) (p<0.001 and p=0.011, respectively). The frequency of systemic symptoms of steroid depletion, such as fatigue and loss of appetite, was also higher in group 1 (94/120 vs. 42/80, p<0.001). Recent steroid injections and loss of appetite were associated with adrenal insufficiency (p=0.002 and p=0.009, respectively). The results of this study revealed a high prevalence of adrenal insufficiency in Korean patients hospitalized for TKA due to end-stage osteoarthritis. Recent steroid injections were causally related to the development of adrenal insufficiency. Therefore, adrenal function should be assessed preoperatively to prevent postoperative complications related to adrenal insufficiency.

The third-person perspective full-body illusion induced by visual-tactile stimulation in virtual reality for stroke patients

This paper attempts to induce the third-person perspective full body illusion (3PP-FBI) with virtual reality (VR) in stroke patients. Nineteen individuals with stroke were recruited. The 3PP-FBI induction method, which was well-established in healthy individuals, using synchronous visual-tactile stimulation on one body part was used. Questionnaire scores and proprioceptive drift values were collected under different conditions for characterizing the induced 3PP-FBI. Results showed that synchronous visual-tactile stimulation of a single body part (back or upper limb) was sufficient to elicit 3PP-FBI in stroke patients, forming a sense of ownership (SOO) over the entire virtual body. Moreover, the intensity of 3PP-FBI was stronger when the back was stimulated, compared to stimulating the impaired upper limb. This study demonstrated the viability of visual-guided rehabilitation training while having a SOO to a virtual body from the third-person perspective, in anticipation of achieving better rehabilitation outcome for movements beyond the first-person perspective.

Brief Submotor-Threshold Electrical Stimulation Applied Synchronously Over Wrist Flexor and Extensor Muscles does Not Suppress Essential Tremor, Independent of Stimulation Frequency.

Electrical stimulation of muscles below motoneuron threshold has shown potential as a low-cost and minimally invasive treatment for Essential Tremor (ET). Prior studies have stimulated wrist flexor and extensor muscles synchronously with diverging results, calling for further investigation. Also, prior studies have only used a narrow range of stimulation parameters, so stimulation parameters have not been optimized. Our purpose was to further investigate synchronous submotor stimulation and identify the effect of stimulation frequency on tremor suppression. We quantified the effect of brief, synchronous stimulation at 15 different frequencies from 10-150 Hz applied over wrist flexors and extensors on both tremor power and frequency in 20 ET patients. We compared tremor power and frequency from hand acceleration and sEMG between pre-, per-, and post-stimulation phases. Our stimulation paradigm did not result in significant tremor suppression or tremor frequency changes at any tested stimulation frequency, showing no significant interaction between phase and stimulation frequency for tremor power measured by either hand acceleration (p = 0.69) or sEMG (p = 0.07). Additionally, the effect of phase interacting with stimulation frequency on tremor frequency was statistically insignificant for acceleration (p = 0.64) and sEMG (p = 0.37). We conclude that brief synchronous submotor-threshold stimulation does not reduce tremor in ET patients, independent of stimulation frequency (from 10 to 150 Hz). Our results are consistent with the hypothesis that brief submotor-threshold stimulation suppresses tremor via reciprocal inhibition, which requires asynchronous stimulation. In contrast, it is hypothesized that synchronous stimulation might require longer stimulation durations to affect supraspinal tremor networks. We studied the effects of synchronous submotor electrical stimulation over wrist flexor and extensor muscles on Essential Tremor. Our results indicate that suppressing tremor with brief synchronous stimulation is ineffective. Based on recently hypothesized mechanisms of peripheral tremor suppression, we hypothesize that asynchronous stimulation or long-duration synchronous stimulation are more effective approaches to peripheral tremor suppression.

No reduction in motor-evoked potential amplitude during the rubber hand illusion.

In the rubber hand illusion (RHI), touches are applied to a fake hand at the same time as touches are applied to a participant's real hand that is hidden in a congruent position. Synchronous (but not asynchronous) tactile stimulation of the two hands may induce the sensation that the fake hand is the participant's own. As such, the illusion is commonly used to examine the sense of body ownership. Some studies indicate that in addition to the subjective experience of limb ownership reported by participants, the RHI can also reduce corticospinal excitability (e.g., as reflected in motor-evoked potential [MEP] amplitude) and alter parietal-motor cortical connectivity in passive participants. These findings have been taken to support a link between motor cortical processing and the subjective experience of body ownership. In this study, we tried to replicate the reduction in MEP amplitude associated with the RHI and uncover the components of the illusion that might explain these changes. As such, we used single-pulse transcranial magnetic stimulation to probe the excitability of the corticospinal motor system as participants experienced the RHI. Despite participants reporting the presence of the illusion and showing shifts in perceived real hand position towards the fake limb supporting its elicitation, we did not observe any associated reduction in MEP amplitude. We conclude that a reduction in MEP amplitude is not a reliable outcome of the RHI and argue that if such effects do occur, they are unlikely to be large or functionally relevant.

Cardiac interoception in infants: Behavioral and neurophysiological measures in various emotional and self-related contexts.

Interoception, the perception of internal bodily signals, is fundamental to our sense of self. Even though theoretical accounts suggest an important role for interoception in the development of the self, empirical investigations are limited, particularly in infancy. Previous studies used preferential-looking paradigms to assess the detection of sensorimotor and multisensory contingencies in infancy, usually related to proprioception and touch. So far, only one recent study reported that infants discriminated between audiovisual stimuli presented synchronously or asynchronously with their heartbeat. This discrimination was related to the amplitude of the infant's heartbeat evoked potentials (HEP), a neural correlate of interoception. In the current study, we measured looking preferences between synchronous and asynchronous visuocardiac (bimodal), and audiovisuocardiac (trimodal) stimuli as well as the HEP in conditions of different emotional contexts and with different degrees of self-relatedness in a mirror-like setup. While the infants preferred trimodal to bimodal stimuli, we did not observe the predicted differences between synchronous and asynchronous stimulation. Furthermore, the HEP was not modulated by emotional context or self-relatedness. These findings do not support previously published results and highlight the need for further studies on the early development of interoception in relation to the development of the self.

Development of a synchronous recording and photo-stimulating electrode in multiple brain neurons.

The investigation of brain networks and neural circuits involves the crucial aspects of observing and modulating neurophysiological activity. Recently, opto-electrodes have emerged as an efficient tool for electrophysiological recording and optogenetic stimulation, which has greatly facilitated the analysis of neural coding. However, implantation and electrode weight control have posed significant challenges in achieving long-term and multi-regional brain recording and stimulation. To address this issue, we have developed a mold and custom-printed circuit board-based opto-electrode. We report successful opto-electrode placement and high-quality electrophysiological recordings from the default mode network (DMN) of the mouse brain. This novel opto-electrode facilitates synchronous recording and stimulation in multiple brain regions and holds promise for advancing future research on neural circuits and networks.

Attentional State-Dependent Peripheral Electrical Stimulation During Action Observation Enhances Cortical Activations in Stroke Patients.

Brain-computer interface (BCI) is a promising technique that enables patients' interaction with computers or machines by analyzing specific brain signal patterns and provides patients with brain state-dependent feedback to assist in their rehabilitation. Action observation (AO) and peripheral electrical stimulation (PES) are conventional methods used to enhance rehabilitation outcomes by promoting neural plasticity. In this study, we assessed the effects of attentional state-dependent feedback in the combined application of BCI-AO with PES on sensorimotor cortical activation in patients after stroke. Our approach involved showing the participants a video with repetitive grasping actions under four different tasks. A mu band suppression (8-13 Hz) corresponding to each task was computed. A topographical representation showed that mu suppression of the dominant (healthy) and affected hemispheres (stroke) gradually became prominent during the tasks. There were significant differences in mu suppression in the affected motor and frontal cortices of the stroke patients. The involvement of both frontal and motor cortices became prominent in the BCI-AO+triggered PES task, in which feedback was given to the patients according to their attentive watching. Our findings suggest that synchronous stimulation according to patient attention is important for neurorehabilitation of stroke patients, which can be achieved with the combination of BCI-AO feedback with PES. BCI-AO feedback combined with PES could be effective in facilitating sensorimotor cortical activation in the affected hemispheres of stroke patients.

Look at me now! Enfacement illusion over computer-generated faces.

According to embodied cognition research, one's bodily self-perception can be illusory and temporarily shifted toward an external body. Similarly, the so-called "enfacement illusion" induced with a synchronous multisensory stimulation over the self-face and an external face can result in implicit and explicit changes in the bodily self. The present study aimed to verify (i) the possibility of eliciting an enfacement illusion over computer-generated faces and (ii) which multisensory stimulation condition was more effective. A total of 23 participants were asked to look at a gender-matched avatar in three synchronous experimental conditions and three asynchronous control conditions (one for each stimulation: visuotactile, visuomotor, and simple exposure). After each condition, participants were asked to complete a questionnaire assessing both the embodiment and the enfacement sensations to address different facets of the illusion. Results suggest a stronger effect of synchronous vs. asynchronous stimulation, and the difference was more pronounced for the embodiment items of the questionnaire. We also found a greater effect of visuotactile and visuomotor stimulations as compared to the simple exposure condition. These findings support the enfacement illusion as a new paradigm to investigate the ownership of different face identities and the specific role of visuotactile and visuomotor stimulations with virtual reality stimuli.

Improvements in classification of left and right foot motor intention using modulated steady-state somatosensory evoked potential induced by electrical stimulation and motor imagery.

In recent years, motor imagery-based brain-computer interface (MI-BCI) has been applied to motor rehabilitation in patients with motor dysfunction. However, traditional MI-BCI is rarely used for foot motor intention recognition because the motor cortex regions of both feet are anatomically close to each other, and traditional event-related desynchronization (ERD) patterns for MI-BCI have insufficient spatial discrimination. This study introduced steady-state somatosensory evoked potentials (SSSEPs) by synchronous bilateral feet electrical stimulation at different frequencies, which were used as carrier signals modulated by unilateral foot motor intention. Fifteen subjects participated in MI and MI-SSSEP tasks. A Riemannian geometry classifier with a task-related component analysis (TRCA) spatial filter was proposed to demodulate the variation in SSSEP features and discriminate the left and right foot motor intentions. The feature outcomes indicated that the amplitude and phase synchronization of the SSSEPs could be well modulated by unilateral foot MI tasks under the MI-SSSEP paradigm. The classification results revealed that the modulated SSSEP features played an important role in the recognition of left-right foot discrimination. Moreover, the proposed TRCA-based method outperformed the other three methods and improved the foot average classification accuracy to 81.07±13.29%, with the highest accuracy attained at 97.00%. Compared with the traditional MI paradigm, the foot motor intention recognition accuracy of the MI-SSSEP paradigm was significantly improved, from nearly 60% to more than 80%. This work provides a practical method for left-right foot motor intention recognition and expands the application of MI-BCI in the field of lower-extremity motor function rehabilitation.

Different armpits under my new nose: Olfactory sex but not gender affects implicit measures of embodiment

Conflicting multisensory signals may alter embodiment to produce self-identification with a foreign body, but the role of olfaction in this process has been overlooked. We studied in healthy participants how sex (male and female sweat odors) and gender (male and female cosmetic scents) olfactory stimuli contribute to embodiment. Participants saw, on a head mounted display, the first-person perspective of a sex mismatching person. Synchronous visuotactile stimulation was applied to enhance illusory embodiment. Simultaneously, they smelled either sex- or gender- congruent or incongruent stimuli. We assessed implicit (skin conductance responses to visual threats) and explicit (questionnaire) measures of embodiment. Stronger responses to threat were found when participants smelled the sex-congruent compared to the sex-incongruent odor, while no such differences were found for the cosmetic scents. According to the questionnaire, embodiment did not differ between conditions. Post-experimental assessment of the presented cues, suggest that while both sweat odors were considered generally male, cosmetic scents were not. The presented scents were generally not associated with the embodied body. Our results suggest that sex-related body odors influence implicit but not explicit aspects of embodiment and are in line with unique characteristics of olfaction in other aspects of cognition.