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BACKGROUND: Previous studies have reported that the sense of "self" is associated with specific brain regions and neural network activities. In addition, the mirror system, which functions when executing or observing an action, might contribute to differentiating the self from others and form the basis of the sense of self as a fundamental physical representation. This study investigated whether differences in mu suppression, an indicator of mirror system activity, reflect cognitions related to self-other discrimination. METHODS: The participants were 30 of healthy college students. The participants observed short video clips of hand movements performed by themselves or actors from two perspectives (i.e., first-person and third-person). The electroencephalogram (EEG) mu rhythm (8-13 Hz) was measured during video observation as an index of mirror neuron system activity. EEG activity related to self-detection was analyzed using participants' hand movements as self-relevant stimuli. RESULTS: The results showed that mu suppression in the 8-13-Hz range exhibited perspective-dependent responses to self/other stimuli. There was a significant self-oriented mu suppression response in the first-person perspective. However, the study found no significant response orientation in the third-person perspective. The results suggest that mirror system activity may involve self-other discrimination differently depending on the perspective. CONCLUSIONS: In summary, this study examined the mirror system's activity for self and others using the EEG's mu suppression. As a result, it was suggested that differences in self and others or perspectives may influence mu suppression.

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The review provides a brief overview of the history of the development of mirror therapy. Current data on the putative mechanisms of mirror therapy as well as the theory of mirror neurons are presented. The authors describe the implementation of the effects of mirror therapy in motor rehabilitation after stroke, including motor imagination or mental simulation of actions, strengthening of spatial attention and self-perception, activation of the ipsilateral corticospinal tract, reorganization of neuronal networks that influence the state of structurally intact but functionally inactive neurons. The authors reflected the prerequisites for the use of mirror therapy in the rehabilitation of cognitive impairment in poststroke patients. The results of current clinical studies and case reports of the use of mirror therapy for the rehabilitation of speech and non-speech cognitive disorders, and neglect syndrome after stroke are presented.

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Mirror neurons show activity during both the execution (AE) and observation of actions (AO). The Mirror Neuron System (MNS) could be involved during motor imagery (MI) as well. Extensive research suggests that the cerebellum is interconnected with the MNS and may be critically involved in its activities. We gathered evidence on the cerebellum's role in MNS functions, both theoretically and experimentally. Evidence shows that the cerebellum plays a major role during AO and MI and that its lesions impair MNS functions likely because, by modulating the activity of cortical inhibitory interneurons with mirror properties, the cerebellum may contribute to visuomotor matching, which is fundamental for shaping mirror properties. Indeed, the cerebellum may strengthen sensory-motor patterns that minimise the discrepancy between predicted and actual outcome, both during AE and AO. Furthermore, through its connections with the hippocampus, the cerebellum might be involved in internal simulations of motor programs during MI. Finally, as cerebellar neuromodulation might improve its impact on MNS activity, we explored its potential neurophysiological and neurorehabilitation implications.

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Engaging in chasing, where an actor actively pursues a target, is considered a crucial activity for the development of social skills. Previous studies have focused predominantly on understanding the neural correlates of chasing from an observer's perspective, but the neural mechanisms underlying the real-time implementation of chasing action remain poorly understood. To gain deeper insights into this phenomenon, the current study employed functional near-infrared spectroscopy (fNIRS) techniques and a novel interactive game. In this interactive game, participants (N = 29) were tasked to engage in chasing behavior by controlling an on-screen character using a gamepad, with the goal of catching a virtual partner. To specifically examine the brain activations associated with the interactive nature of chasing, we included two additional interactive actions: following action of following the path of a virtual partner and free action of moving without a specific pursuit goal. The results revealed that chasing and following actions elicited activation in a broad and overlapping network of brain regions, including the temporoparietal junction (TPJ), medial prefrontal cortex (mPFC), premotor cortex (PMC), primary somatosensory cortex (SI), and primary motor cortex (M1). Crucially, these regions were found to be modulated by the type of interaction, with greater activation and functional connectivity during the chasing interaction than during the following and free interactions. These findings suggested that both the MNS, encompassing regions such as the PMC, M1 and SI, and the mentalizing system (MS), involving the TPJ and mPFC, contribute to the execution of online chasing actions. Thus, the present study represents an initial step toward future investigations into the roles of MNS and MS in real-time chasing interactions.

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Motor issues are frequently observed accompanying core deficits in autism spectrum disorder (ASD). Impaired motor behavior has also been linked to cognitive and social abnormalities, and problems with predictive ability have been suggested to play an important, possibly shared, part across all these domains. Brain imaging of sensory-motor behavior is a promising method for characterizing the neurobiological foundation for this proposed key trait. The present functional magnetic resonance imaging (fMRI) developmental study, involving children/youth with ASD, typically developing (TD) children/youth, and neurotypical adults, will investigate brain activations during execution and observation of a visually guided, goal-directed sequential (two-step) manual task. Neural processing related to both execution and observation of the task, as well as activation patterns during the preparation stage before execution/observation will be investigated. Main regions of interest include frontoparietal and occipitotemporal cortical areas, the human mirror neuron system (MNS), and the cerebellum.

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Neurofeedback training (NFT) is a promising adjuvant intervention method. The desynchronization of mu rhythm (8-13 Hz) in the electroencephalogram (EEG) over centro-parietal areas is known as a valid indicator of mirror neuron system (MNS) activation, which has been associated with social skills. Still, the effect of neurofeedback training on the MNS requires to be well investigated. The present study examined the possible impact of NFT with a mu suppression training protocol encompassing 15 NFT sessions (45 min each) on 16 healthy neurotypical participants. In separate pre- and post-training sessions, 64-channel EEG was recorded while participants (1) observed videos with various types of movements (including complex goal-directed hand movements and social interaction scenes) and (2) performed the "Reading the Mind in the Eyes Test" (RMET). EEG source reconstruction analysis revealed statistically significant mu suppression during hand movement observation across MNS-attributed fronto-parietal areas after NFT. The frequency analysis showed no significant mu suppression after NFT, despite the fact that numerical mu suppression appeared to be visible in a majority of participants during goal-directed hand movement observation. At the behavioral level, RMET accuracy scores did not suggest an effect of NFT on the ability to interpret subtle emotional expressions, although RMET response times were reduced after NFT. In conclusion, the present study exhibited preliminary and partial evidence that mu suppression NFT can induce mu suppression in MNS-attributed areas. More powerful experimental designs and longer training may be necessary to induce substantial and consistent mu suppression, particularly while observing social scenarios.

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PURPOSE: To identify the effects of mirror neuron activation (MNAT) combined or not with physical exercise (PE) in healthy older adults, on functionality, balance, gait velocity and risk of falls. METHODS: A systematic electronic search was performed in PubMed/MEDLINE, Cochrane, and Embase databases. RESULTS: Thirteen randomized controlled trials were included in the qualitative analysis, and eleven in the quantitative analysis. All studies showed fair to high quality and the most frequent high-risk bias was "Blinding of participants and personnel". Compared to the control condition, higher improvement was shown in older people who received MNAT, on functionality (1.57 [0.57, 2.62], balance (1.95 [1.32, 2.572]), and gait velocity (1.20 [0.30, 2.11]). Compared to PE, MNAT combined with PE does not improve functionality. More studies are needed to assess MNAT effectiveness in the rest of the outcomes. CONCLUSIONS: Neuron system activation through MNAT improves relevant abilities in older adults, with better results when including functional activities. However, the beneficial effects on these variables of adding MNAT to a PE program are controversial.

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Are there brain regions that are specialized for the execution of imitative actions? We compared two hypotheses of imitation: the mirror neuron system (MNS) hypothesis predicts frontal and parietal engagement which is specific to imitation, while the Grist-Mills hypothesis predicts no difference in brain activation between imitative and matched non-imitative actions. Our delayed imitation fMRI paradigm included two tasks, one where correct performance was defined by a spatial rule and another where it was defined by an item-based rule. For each task, participants could learn a sequence from a video of a human hand performing the task, from a matched "Ghost" condition, or from text instructions. When participants executed actions after seeing the Hand demonstration (compared to Ghost and Text demonstrations), no activation differences occurred in frontal or parietal regions; rather, activation was localized primarily to occipital cortex. This adds to a growing body of evidence which indicates that imitation-specific responses during action execution do not occur in canonical mirror regions, contradicting the mirror neuron system hypothesis. However, activation differences did occur between action execution in the Hand and Ghost conditions outside MNS regions, which runs counter to the Grist-Mills hypothesis. We conclude that researchers should look beyond these hypotheses as well as classical MNS regions to describe the ways in which imitative actions are implemented by the brain.

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According to the mirror mechanism the discharge of F5 mirror neurons of a monkey observing another individual performing an action is a motor representation of the observed action that may serve to understand or learn from the action. This hypothesis, if strictly interpreted, requires mirror neurons to exhibit an action tuning that is shared between action observation and execution. Due to insufficient data it remains contentious if this requirement is met. To fill in the gaps, we conducted an experiment in which identical objects had to be manipulated in three different ways in order to serve distinct action goals. Using three methods, including cross-task classification, we found that at most time points F5 mirror neurons did not encode observed actions with the same code underlying action execution. However, in about 20% of neurons there were time periods with a shared code. These time periods formed a distinct cluster and cannot be considered a product of chance. Population classification yielded non-shared coding for observed actions in the whole population, which was at times optimal and consistently better than shared coding in differentially selected subpopulations. These results support the hypothesis of a representation of observed actions based on a strictly defined mirror mechanism only for small subsets of neurons and only under the assumption of time-resolved readout. Considering alternative concepts and recent findings, we propose that during observation mirror neurons represent the process of a goal pursuit from the observer's viewpoint. Whether the observer's goal pursuit, in which the other's action goal becomes the observer's action goal, or the other's goal pursuit is represented remains to be clarified. In any case, it may allow the observer to use expectations associated with a goal pursuit to directly intervene in or learn from another's action.

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The mirror neuron system (MNS), including the inferior frontal gyrus (IFG), inferior parietal lobule (IPL) and superior temporal sulcus (STS) plays an important role in action representation and imitation and may be dysfunctional in autism spectrum disorder (ASD). However, it's not clear how these three regions respond and interact during the imitation of different basic facial expressions and whether the pattern of responses is influenced by autistic traits. Thus, we conducted a natural facial expression (happiness, angry, sadness and fear) imitation task in 100 healthy male subjects where expression intensity was measured using facial emotion recognition software (FaceReader) and MNS responses were recorded using functional near-infrared spectroscopy (fNIRS). Autistic traits were measured using the Autism Spectrum Quotient questionnaire. Results showed that imitation of happy expressions produced the highest expression intensity but a small deactivation in MNS responses, suggesting a lower processing requirement compared to other expressions. A cosine similarity analysis indicated a distinct pattern of MNS responses during imitation of each facial expression with functional intra-hemispheric connectivity between the left IPL and left STS being significantly higher during happy compared to other expressions, while inter-hemispheric connectivity between the left and right IPL differed between imitation of fearful and sad expressions. Furthermore, functional connectivity changes during imitation of each different expression could reliably predict autistic trait scores. Overall, the results provide evidence for distinct patterns of functional connectivity changes between MNS regions during imitation of different emotions which are also associated with autistic traits.

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The association between social cognition and putative mirror neuron system (MNS)-activity in major psychoses might be contingent upon frontal dysregulation. We used a transdiagnostic ecological approach to enrich a specific behavioral phenotype (echophenomena or hyper-imitative states) across clinical diagnoses (mania and schizophrenia) to compare behavioral and physiological markers of social cognition and frontal disinhibition. We examined 114 participants with schizophrenia (N = 53) and mania (N = 61) for the presence and severity of echo-phenomena (echopraxia, incidental, and induced echolalia) using an ecological paradigm to simulate real-life social communication. Symptom severity, frontal release reflexes, and theory of mind performance were also assessed. In a proportion of these participants with (N = 20) and without (N = 20) echo-phenomena, we compared motor resonance (motor evoked potential facilitation during action observation compared to static image viewing) and cortical silent period (CSP) as putative markers of MNS-activity and frontal disinhibition, respectively, using Transcranial Magnetic Stimulation. While the prevalence of echo-phenomena was similar between mania and schizophrenia, incidental echolalia was more severe in mania. Participants with echo-phenomena (compared to those without) had significantly greater motor resonance with singlepulse (not with paired-pulse) stimuli, poorer theory of mind scores, higher frontal release reflexes but similar CSP, and greater symptom severity. None of these parameters significantly differed between participants with mania and schizophrenia. We observed relatively better phenotypic and neurophysiological characterization of major psychoses by categorizing participants based on the presence of echophenomena than clinical diagnoses. Higher putative MNS-activity was associated with poorer theory of mind in a hyper-imitative behavioral state.

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Broadly congruent mirror neurons, responding to any grasp movement, and strictly congruent mirror neurons, responding only to specific grasp movements, have been reported in single-cell studies with primates. Delineating grasp properties in humans is essential to understand the human mirror neuron system with implications for behavior and social cognition. We analyzed electrocorticography data from a natural reach-and-grasp movement observation and delayed imitation task with 3 different natural grasp types of everyday objects. We focused on the classification of grasp types from high-frequency broadband mirror activation patterns found in classic mirror system areas, including sensorimotor, supplementary motor, inferior frontal, and parietal cortices. Classification of grasp types was successful during movement observation and execution intervals but not during movement retention. Our grasp type classification from combined and single mirror electrodes provides evidence for grasp-congruent activity in the human mirror neuron system potentially arising from strictly congruent mirror neurons.

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Background/aim: The firing rate of the mirror neuron system in monkeys decreases systematically with more repetitions. The aim of this study is to investigate whether the activity of the mirror neuron system varies based on the observed movement and the contents of the action, as well as whether there is inhibition in the mirror neuron system when humans observe repeated actions. If inhibition is present, the second question of the study is whether it is related to the organization of the observed action. Materials and methods: Fourteen healthy volunteers participated in the study. Transcranial magnetic stimulation was applied to the left primary motor cortex and motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous and abductor pollicis brevis muscles while the participants were watching videos specially prepared for the study. Results: There were no significant changes in MEP amplitudes compared to baseline MEPs while observing aimless action. However, while participants watched the repeated action video, the mean MEP amplitude increased at the beginning of the movement, but neither facilitation nor inhibition was detected when the participants watched the phase of grasping the object of the action compared to the baseline MEP amplitude. On the other hand, while participants were watching different activities, an increased MEP amplitude was observed at the beginning of the movement and in the grasping of the object of the action. Additionally, there was no significant reduction in MEP amplitude during any movement stages while observing the repeated action video. Conclusion: The findings of this study suggest that the activation of the mirror neuron system in humans depends on the content and stages of the observed movement. Additionally, there was no inhibition or systematic reduction in MEP amplitudes while watching a repeated action.

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Social learning in the forms of imitative and contagious behaviors are essential for learning abilities and social interaction. However, children with neurodevelopmental disorders and intellectual disabilities show impairments in these behaviors, which profoundly affect their communication skills and cognitive functions. Although these deficits are well studied in humans, pre-clinical animal model assessments of imitative and contagious behavioral deficits are limited. Here, we first define various forms of social learning as well as their developmental and evolutionary significance in humans. We also explore the impact of imitative and contagious behavioral deficits in several neurodevelopmental disorders associated with autistic-like symptoms. Second, we highlight imitative and contagious behaviors observed in nonhuman primates and other social animals commonly used as models for neurodevelopmental disorders. Lastly, we conceptualize these behaviors in the contexts of mirror neuron activity, learning, and empathy, which are highly debated topics. Taken together, this review furthers the understanding of imitative and contagious behaviors. We hope to prompt and guide future behavioral studies in animal models of neurodevelopmental disorders.

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Cognitive skills and the underlying neural architecture are under the influence of genetics. Cognitive genomics research explores the triadic relationship between genes, brain, and cognition, with its major strategy being genotype-driven. Here we show that an inverse strategy is feasible to identify novel candidate genes for particular neuro-cognitive phenotypes in macaques. Two monkeys, originally involved in separate psychological studies, exhibited learning delay and low levels of social performance monitoring. In one monkey, mirror neurons were fewer compared to controls and mu suppression was absent in the frontal cortex. The other monkey showed heightened visual responsiveness in both frontal cortex and dopamine-rich midbrain, with a lack of inter-areal synchronization. Exome analyses revealed that the two monkeys were most likely cousins and shared variants in MAP2, APOC1, and potentially HTR2C. This phenotype-driven strategy in cognitive genomics provides a useful means to clarify the genetic basis of phenotypic variation and develop macaque models of neuropsychiatric disorders.

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Mirror neurons have been associated with empathy. People with psychopathic traits present low levels of empathy. To analyze this, a systematic review of fMRI studies of people with psychopathic traits during an emotional facial expression processing task was performed. The regions of interest were structures associated with the mirror neuron system: ventromedial prefrontal cortex (vmPFC), inferior parietal lobe (IPL), inferior frontal gyrus and superior temporal sulcus. The analysis was also extended to structures related to affective empathy (insula, amygdala and anterior cingulate cortex) and to two more emotional processing areas (orbitofrontal cortex and fusiform gyrus). Hypoactivation was more frequently observed in regions of the mirror neuron system from people with high psychopathic traits, as well as in the emotional processing structures, and those associated with affective empathy, except for the insula, where it presented higher activity. Differences were observed for all types of emotions. The results suggest that the mirror neuron system is altered in psychopathy and their relationship with affective empathy deficits is discussed.

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In experiments on observing and performing social gestures, the level of mu rhythm suppression is associated with the activity of the mirror neuron system (MNS), which is responsible for the perception and understanding of nonverbal signals in social communication. In turn, while MNS activity may be associated primarily with empathy, it is also associated with other psychological and demographic factors affecting the effectiveness of cortical neural networks. In this study, we verified the influence of empathy, state and trait anxiety levels, presence and number of children, and age on the mu-suppression level in 40 women. We used 32-channel EEG recorded during observation, and synchronous execution of various hand movements. The ICA infomax method was used for decomposing and selecting the left hemisphere component of the mu-rhythm. Mu-suppression was higher in women with one child, with higher levels of empathy, and with lower anxiety levels. It is possible that MNS activity is stronger in women during parental care.

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BACKGROUND: The Action Observation Therapy (AOT) is a well-established post-stroke rehabilitation treatment based on the theoretical framework of the Mirror Neuron System (MNS) activation. However, AOT protocols are still heterogeneous in terms of video contents of observed actions. OBJECTIVE: The aim of this study was to analyze electroencephalographic (EEG) recordings in stroke patients during the observation of different videos of task-specific upper limb movements, and to define which category of actions can elicit a stronger cortical activation in the observer's brain. METHODS: Signals were analyzed from 19 chronic stroke subjects observing customized videos that represented 3 different categories of upper limb actions: Finalized Actions, Non-Finalized Actions, and Control Videos. The Event-Related Desynchronization in the µ and ß bands was chosen to identify the involvement of the cerebral cortex: the area of the normalized power spectral density was calculated for each category and, deepening, for the reaching and completion sub-phases of Finalized Actions. For descriptive purposes, the time course of averaged signal power was described. The Kruskal-Wallis test (P < .05) was applied. RESULTS: The analysis showed a greater desynchronization when subjects observed Finalized Actions with respect to Non-Finalized in all recorded areas; Control videos provoked a synchronization in the same areas and frequency bands. The reaching phase of feeding and self-care actions evoked a greater suppression both in µ and ß bands. CONCLUSIONS: The observation of finalized arm movements seems to elicit the strongest activation of the MNS in chronic stroke patients. This finding may help the clinicians to design future AOT-based stroke rehabilitation protocols. CLINICAL TRIAL REGISTRATION: Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT04047134.

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