Multisensory Integration of Anticipated Cardiac Signals with Visual Targets Affects Their Detection among Multiple Visual Stimuli

Many studies have elucidated the multisensory processing of different exteroceptive signals (e.g., auditory-visual stimuli), but less is known about the multisensory integration of interoceptive signals with exteroceptive information. Here, we investigated the perceptual outcomes and electrophysiological brain mechanisms of cardio-visual integration by using participants’ electrocardiogram signals to control the color change of a visual target in dynamically changing displays. Reaction times increased when the target change coincided with strong cardiac signals concerning the state of cardiovascular arousal (i.e., presented at the end of ventricular systole), compared to when the target change occurred at a time when cardiac arousal was relatively low (i.e., presented at the end of ventricular diastole). Moreover, the concurrence of the target change and cardiac arousal signals modulated the event-related potentials and the beta power in an early period (~100 ms after stimulus onset), and decreased the N2pc and the beta lateralization in a later period (~200 ms after stimulus onset). Our results suggest that the multisensory integration of anticipated cardiac signals with a visual target negatively affects its detection among multiple visual stimuli, potentially by suppressing sensory processing and reducing attention toward the visual target. This finding highlights the role of cardiac information in visual processing and furthers our understanding of the brain dynamics underlying multisensory perception involving both interoception and exteroception

Brain-body interactions in perception and action

How we perceive and react to the environment is not fixed; instead, it changes dynamically. This variability can be attributed to various factors operating at conscious and subconscious levels. Interoception, the processing of internal bodily signals such as heartbeats, has been found to modulate perception and action. However, the findings are partly inconsistent, and the underlying neural mechanisms are largely unclear. Sense of agency, the feeling of control over our actions and their outcomes, has also been found to shape our actions. Nevertheless, whether and how changes in our sense of agency influence our capacity to regulate behavior flexibly are largely unknown. The present thesis investigates the effects of cardiac interoception and the sense of agency on visual perception and action regulation. It includes five studies with behavioral and electrophysiological data from healthy human participants. The Influence of Cardiac Interoception on Visual Perception (Study I and Study II) In Study I, we investigated the perceptual effects and electrophysiological mechanisms of cardio-visual integration by coupling the color change of a visual target with participants' heartbeats in dynamically changing displays. Participants' task was to identify the orientation of the visual target. We found that (i) reaction times increased when the target change coincided with strong cardiac signals (during systole), compared to when the target change occurred at a time when cardiac signals were relatively weak (during diastole); (ii) the co-occurrence of the target change and cardiac signals modulated the ERP amplitude and the beta power in an early period (~100 ms after stimulus onset), and decreased the lateralized N2pc amplitude and the lateralized beta power in a later period (~200 ms after stimulus onset). Our results suggest that the multisensory integration of anticipated cardiac signals with a visual target negatively affects its detection among multiple visual stimuli, potentially by suppressing sensory processing and reducing attention toward the visual target. In study II, we investigated the spontaneous shifts of attention between the internal and external environment across the cardiac cycle. Two groups of flickering dots moved continuously and changed direction dynamically within the same spatial location of the screen. However, only the direction change of one group of dots was coupled with participants' heartbeats. Participants' task was to detect a brief color change in the moving dots. We found that (i) compared to the visual dots whose direction change occurred randomly within the cardiac cycle, the dots coincided with strong cardiac signals (during systole) induced decreased SSVEP power, while the dots that coincided with weak cardiac signals (during diastole) induced increased SSVEP phase synchronization; (ii) the coupling of visual stimuli to the systole led to a larger HEP but a smaller N2 component evoked by the color change; (iii) the increase in HEP amplitude was related to the decrease in N2 amplitude. Our results suggest cardiac signals automatically redirect attention from external to internal domains. Both studies reveal the interplay between cardiac processing and visual processing and support the spontaneous shifts of attention between interoception and exteroception across the cardiac cycle. The Influence of Cardiac Interoception on Action Regulation (Study Ⅲ) In study Ⅲ, we investigated how cardiac signals influence response inhibition in a stop-signal task by coupling the occurrence of the stop signal with participants' heartbeats. The stop signal signified the cancellation of the prepotent motor response. We observed prolonged stop-signal reaction times, reduced stop-signal P3 amplitudes, and higher HEP amplitudes when the stop signal was presented during cardiac systole, compared to presentation randomly within the cardiac cycle. Furthermore, these effects were independent of the emotional attribute of the stop signal (emotional facial expression change or non-emotional color change). Our results suggest that the co-occurrence of the action-relevant external cue and cardiac signals makes it harder to cancel the prepotent motor behavior. This effect may be attributed to inhibited perceptual processes of the visual cue, heightened readiness for action, or impaired inhibitory control ability during systole. This study reveals the impact of cardiac signals on response inhibition and supports the attentional trade-off mechanism between interoception and exteroception. The Influence of Sense of Agency on Action Regulation (Study Ⅳ and Study Ⅴ) Both Study Ⅳ and Study Ⅴ investigated the effect of the sense of agency on subsequent action regulation by adopting modified go/no-go tasks. The first experiment of Study Ⅳ modulated participants' sense of agency by varying the occurrence of action outcomes (present vs. absent) both locally on a trial-by-trial basis and globally regarding the overall probability of action outcomes within a block of trials (high vs. low). When participants' previous action led to an outcome (i.e., a happy face) compared with no outcome, they responded more accurately and faster to go cues, reacted less accurately to no-go cues, and made go decisions more frequently and faster to free-choice cues. These effects were even stronger when action outcomes occurred more frequently in a given block or several previous trials. The second experiment of Study Ⅳ further demonstrated that the effects of outcome presence on subsequent action regulation were independent of the emotional valence of the action outcome (a happy or an angry face). Taken together, Study Ⅳ provides behavioral evidence that a higher sense of agency as induced by the presence of action outcomes enhanced action readiness and suppressed response inhibition. Study Ⅴ manipulated participants' sense of agency by varying the presence, predictability, and emotional valence of a visual outcome for a given motor action. Consistent with the results of Study Ⅳ, when participants unexpectedly did not receive any visible outcome following their action, they exhibited slower responses and lower hit rates to the subsequent go signal but higher rates of successful inhibition to the subsequent no-go signal, regardless of the emotional valence of the expected action outcome. Furthermore, enhanced inhibitory tendencies were accompanied by reduced N2 and P3 amplitudes, midfrontal theta power, and theta synchronization between midfrontal and medial-to-parietal areas, indicating that less top-down control is required for successful response inhibition after experiencing a low sense of agency. These findings suggest that feeling less in control in a preceding trial makes it easier to implement inhibitory control in the current trial. Both studies reveal the facilitatory effect of sense of agency on subsequent action readiness and its inhibitory effect on subsequent response inhibition, and they uncover how the automatic evaluation of action effectiveness shapes our ability to regulate actions flexibly. General Conclusions Overall, the present thesis suggests that fluctuations in internal bodily signals can influence perception and action, indicating a strong link between mind and body. Additionally, the effectiveness of motor action can shape subsequent action tendencies. These findings shed new light on the theory of embodied cognition

Different priming effects of empathy on neural processing associated with firsthand pain and nonpain perception

The shared-representation model of empathy is still debated. One of the major questions is whether empathy-eliciting stimuli depicting others&#39; pain selectively activate the representations of self-pain. To address this issue, we assessed the priming effects of empathy-eliciting pictures on firsthand pain and nonpain perception, as well as its associated neural processing. In Experiment 1, when compared with nonpainful pictures depicting individuals&#39; body parts with no injury, participants primed by painful pictures showing individuals&#39; body parts with injury reported higher ratings for perceived intensity, unpleasantness, and salience of nociceptive and auditory stimuli, but they only exhibited increased N2 amplitude in response to nociceptive stimuli. In Experiment 2, the results from another group of participants replicated the observations of Experiment 1 and validated the findings in the non-nociceptive somatosensory modality. Importantly, participants&#39; concern ratings for priming pictures predicted their unpleasantness ratings for subsequent nociceptive stimuli, while participants&#39; attention ratings predicted their unpleasantness ratings for subsequent auditory and tactile stimuli. This finding implies that empathy for pain might influence pain and nonpain perception via different psychological mechanisms. In summary, our findings highlight the existence of pain-selective representations in empathy for pain and contribute to a better understanding of the shared-representation model of empathy.</p

Impact Factors of Empathy in Mainland Chinese Youth

Empathy was investigated in 592 Mainland Chinese youth using the Interpersonal Reactivity Index. Participants&#39; empathy-related information covering demographic traits, emotional wellness, as well as academic and social problems were recorded. Results of Classification and Regression Tree (CART) analysis showed that emotional empathy, cognitive empathy, and empathy-related personal distress was impacted by inherited traits (e.g., sex), acquired traits (e.g., study major), and a combination of both aspects, respectively. Moreover, empathy was found to be higher in youth in a vulnerable social position (i.e., outlander, female, and ethnic minority) than those in a dominant one (i.e., local, male, and ethnic majority). It was also found that personal distress, rather than empathy, was significantly correlated with academic, social, and emotional problems in the youth cohort. Hence, the current study provided an innovative observation of the relationships between empathy, personal distress, ethnicity, social vulnerability, wellness, study major, and other key characteristics in Mainland Chinese youth.</p

Transcutaneous Electrical Nerve Stimulation in Relieving Neuropathic Pain: Basic Mechanisms and Clinical Applications

Purpose of Review Transcutaneous electrical nerve stimulation (TENS) is widely used as a non-pharmacological approach for pain relief in a variety of clinical conditions. This manuscript aimed to review the basic mechanisms and clinical applications regarding the use of TENS for alleviating the peripheral (PNP) and central neuropathic pain (CNP). Recent Findings Basic studies on animal models showed that TENS could alleviate pain by modulating neurotransmitters and receptors in the stimulation site and its upper levels, including the spinal cord, brainstem, and brain. Besides, many clinical studies have investigated the efficacy of TENS in patients with CNP (caused by spinal cord injury, stroke, or multiple sclerosis) and PNP (induced by diabetes, cancer, or herpes zoster). Most clinical trials have demonstrated the efficacy of TENS in attenuating neuropathic pain and suggested that appropriate stimulation parameters (e.g., stimulation frequency and intensity) were critical to improving the analgesic effects of TENS. However, there are some conflicting findings related to the efficacy of TENS in relieving neuropathic pain. With optimized stimulation parameters, TENS would be effective in attenuating neuropathic pain. To obtain sufficient evidence to support the use of TENS in the clinic, researchers recommended performing multicenter clinical trials with optimized TENS protocols for the treatment of various CNP and PNP.</p

Evaluating Cortical Alterations in Patients With Chronic Back Pain Using Neuroimaging Techniques: Recent Advances and Perspectives

Chronic back pain (CBP) is a leading cause of disability and results in considerable socio-economic burdens worldwide. Although CBP patients are commonly diagnosed and treated with a focus on the &ldquo;end organ dysfunction&rdquo; (i.e., peripheral nerve injuries or diseases), the evaluation of CBP remains ?awed and problematic with great challenges. Given that the peripheral nerve injuries or diseases are insuf?cient to de?ne the etiology of CBP in some cases, the evaluation of alterations in the central nervous system becomes particularly necessary and important. With the development of advanced neuroimaging techniques, extensive studies have been carried out to identify the cortical abnormalities in CBP patients. Here, we provide a comprehensive overview on a series of novel ?ndings from these neuroimaging studies to improve our understanding of the cortical abnormalities originated in the disease. First, CBP patients normally exhibit central sensitization to external painful stimuli, which is indexed by increased pain sensitivity and brain activations in pain-related brain regions. Second, long-term suffering from chronic pain leads to emotional disorders, cognitive impairments, and the abnormalities of the relevant brain networks among CBP patients. Third, CBP is associated with massive cortical reorganization, including structural, functional, and metabolic brain changes. Overall, a deep insight into the neural mechanisms underlying the development and outcome of CBP through more sophisticated neuroimaging investigations could not only improve our current understanding of the etiology of CBP but also facilitate the diagnosis and treatment of CBP based on precision medicine.</p

Distinct and common mechanisms of cross-model semantic conflict and response conflict in an auditory relevant task

The mechanisms of semantic conflict and response conflict in the Stroop task have mainly been investigated in the visual modality. However, the understanding of these mechanisms in cross-modal modalities remains limited. In this electroencephalography (EEG) study, an audiovisual 2-1 mapping Stroop task was utilized to investigate whether distinct and/or common neural mechanisms underlie cross-modal semantic conflict and response conflict. The response time data showed significant effects on both cross-modal semantic and response conflicts. Interestingly, the magnitude of semantic conflict was found to be smaller in the fast response time bins than in the slow response time bins, whereas no such difference was observed for response conflict. The EEG data demonstrated that cross-modal semantic conflict specifically increased the N450 amplitude. However, cross-modal response conflict specifically enhanced theta band power and theta phase synchronization between the medial frontal cortex (MFC) and lateral prefrontal electrodes as well as between the MFC and motor electrodes. In addition, both cross-modal semantic conflict and response conflict led to a decrease in P3 amplitude. Taken together, these findings provide cross-modal evidence for domain-specific mechanism in conflict detection and suggest both domain-specific and domain-general mechanisms exist in conflict resolution