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Kilteni K, Engeler P, Boberg I, Maurex L, Ehrsson HH. No evidence for somatosensory attenuation during action observation of self-touch. Eur J Neurosci 2021; 54:6422-6444. [PMID: 34463971 DOI: 10.1111/ejn.15436] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 08/12/2021] [Accepted: 08/13/2021] [Indexed: 11/28/2022]
Abstract
The discovery of mirror neurons in the macaque brain in the 1990s triggered investigations on putative human mirror neurons and their potential functionality. The leading proposed function has been action understanding: Accordingly, we understand the actions of others by 'simulating' them in our own motor system through a direct matching of the visual information to our own motor programmes. Furthermore, it has been proposed that this simulation involves the prediction of the sensory consequences of the observed action, similar to the prediction of the sensory consequences of our executed actions. Here, we tested this proposal by quantifying somatosensory attenuation behaviourally during action observation. Somatosensory attenuation manifests during voluntary action and refers to the perception of self-generated touches as less intense than identical externally generated touches because the self-generated touches are predicted from the motor command. Therefore, we reasoned that if an observer simulates the observed action and, thus, he/she predicts its somatosensory consequences, then he/she should attenuate tactile stimuli simultaneously delivered to his/her corresponding body part. In three separate experiments, we found a systematic attenuation of touches during executed self-touch actions, but we found no evidence for attenuation when such actions were observed. Failure to observe somatosensory attenuation during observation of self-touch is not compatible with the hypothesis that the putative human mirror neuron system automatically predicts the sensory consequences of the observed action. In contrast, our findings emphasize a sharp distinction between the motor representations of self and others.
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Affiliation(s)
| | - Patrick Engeler
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Ida Boberg
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Linnea Maurex
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - H Henrik Ehrsson
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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Is the Putative Mirror Neuron System Associated with Empathy? A Systematic Review and Meta-Analysis. Neuropsychol Rev 2020; 31:14-57. [PMID: 32876854 DOI: 10.1007/s11065-020-09452-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Accepted: 08/09/2020] [Indexed: 12/18/2022]
Abstract
Theoretical perspectives suggest that the mirror neuron system (MNS) is an important neurobiological contributor to empathy, yet empirical support is mixed. Here, we adopt a summary model for empathy, consisting of motor, emotional, and cognitive components of empathy. This review provides an overview of existing empirical studies investigating the relationship between putative MNS activity and empathy in healthy populations. 52 studies were identified that investigated the association between the MNS and at least one domain of empathy, representing data from 1044 participants. Our results suggest that emotional and cognitive empathy are moderately correlated with MNS activity, however, these domains were mixed and varied across techniques used to acquire MNS activity (TMS, EEG, and fMRI). Few studies investigated motor empathy, and of those, no significant relationships were revealed. Overall, results provide preliminary evidence for a relationship between MNS activity and empathy. However, our findings highlight methodological variability in study design as an important factor in understanding this relationship. We discuss limitations regarding these methodological variations and important implications for clinical and community translations, as well as suggestions for future research.
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I'll cry instead: Mu suppression responses to tearful facial expressions. Neuropsychologia 2020; 143:107490. [PMID: 32387069 DOI: 10.1016/j.neuropsychologia.2020.107490] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 03/27/2020] [Accepted: 05/04/2020] [Indexed: 01/18/2023]
Abstract
Tears are a facial expression of emotion that readily elicit empathic responses from observers. It is currently unknown whether these empathic responses to tears are influenced by specific neural substrates. The EEG mu rhythm is one method of investigating the human mirror neuron system, purported to underlie the sharing of affective states and a facilitator of social cognition. The purpose of this research was to explore the mu response to tearful expressions of emotion. Sixty-eight participants viewed happy and sad faces, both with and without tears, in addition to a neutral control condition. Participants first completed an emotion discrimination task, and then an imitation condition where they were required to mimic the displayed expression. Mu enhancement was found in response to the discrimination task, whilst suppression was demonstrated in response to the imitation condition. Examination of the suppression scores revealed that greater suppression was observed in response to happy-tear and sad tear-free expressions. Planned contrasts exploring suppression to neutral faces revealed no significant differences between emotional and neutral conditions. The mu response to neutral expressions resembled that of the happy-tear and the sad tear-free conditions, lending support to the idea that ambiguous emotional expressions require greater sensorimotor engagement. This study provides preliminary evidence for the role of the mirror neuron system in discerning tearful expressions of emotion in the absence of context.
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Hobson HM, Bishop DVM. Reply to Bowman et al.: Building the foundations for moving mu suppression research forward. Cortex 2017; 96:126-128. [PMID: 28751100 DOI: 10.1016/j.cortex.2017.06.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Revised: 06/13/2017] [Accepted: 06/14/2017] [Indexed: 10/19/2022]
Affiliation(s)
- Hannah M Hobson
- Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience, London, King's College London, 16 De Crespigny Park, London, SE5 8AF, UK.
| | - Dorothy V M Bishop
- Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford, OX1 3UD, UK
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Hobson HM, Bishop DVM. The interpretation of mu suppression as an index of mirror neuron activity: past, present and future. ROYAL SOCIETY OPEN SCIENCE 2017; 4:160662. [PMID: 28405354 PMCID: PMC5383811 DOI: 10.1098/rsos.160662] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Accepted: 02/01/2017] [Indexed: 06/01/2023]
Abstract
Mu suppression studies have been widely used to infer the activity of the human mirror neuron system (MNS) in a number of processes, ranging from action understanding, language, empathy and the development of autism spectrum disorders (ASDs). Although mu suppression is enjoying a resurgence of interest, it has a long history. This review aimed to revisit mu's past, and examine its recent use to investigate MNS involvement in language, social processes and ASDs. Mu suppression studies have largely failed to produce robust evidence for the role of the MNS in these domains. Several key potential shortcomings with the use and interpretation of mu suppression, documented in the older literature and highlighted by more recent reports, are explored here.
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Mu suppression - A good measure of the human mirror neuron system? Cortex 2016; 82:290-310. [PMID: 27180217 PMCID: PMC4981432 DOI: 10.1016/j.cortex.2016.03.019] [Citation(s) in RCA: 150] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Revised: 03/23/2016] [Accepted: 03/23/2016] [Indexed: 12/19/2022]
Abstract
Mu suppression has been proposed as a signature of the activity of the human mirror neuron system (MNS). However the mu frequency band (8–13 Hz) overlaps with the alpha frequency band, which is sensitive to attentional fluctuation, and thus mu suppression could potentially be confounded by changes in attentional engagement. The specific baseline against which mu suppression is assessed may be crucial, yet there is little consistency in how this is defined. We examined mu suppression in 61 typical adults, the largest mu suppression study so far conducted. We compared different methods of baselining, and examined activity at central and occipital electrodes, to both biological (hands) and non-biological (kaleidoscope) moving stimuli, to investigate the involvement of attention and alpha activity in mu suppression. We also examined changes in beta power, another candidate index of MNS engagement. We observed strong mu suppression restricted to central electrodes when participants performed hand movements, demonstrating that mu is indeed responsive to the activity of the motor cortex. However, when we looked for a similar signature of mu suppression to passively observed stimuli, the baselining method proved to be crucial. Selective suppression for biological versus non-biological stimuli was seen at central electrodes only when we used a within-trial baseline based on a static stimulus: this method greatly reduced trial-by-trial variation in the suppression measure compared with baselines based on blank trials presented in separate blocks. Even in this optimal condition, 16–21% of participants showed no mu suppression. Changes in beta power also did not match our predicted pattern for MNS engagement, and did not seem to offer a better measure than mu. Our conclusions are in contrast to those of a recent meta-analysis, which concluded that mu suppression is a valid means to examine mirror neuron activity. We argue that mu suppression can be used to index the human MNS, but the effect is weak and unreliable and easily confounded with alpha suppression.
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Fox NA, Bakermans-Kranenburg MJ, Yoo KH, Bowman LC, Cannon EN, Vanderwert RE, Ferrari PF, van IJzendoorn MH. Assessing human mirror activity with EEG mu rhythm: A meta-analysis. Psychol Bull 2015; 142:291-313. [PMID: 26689088 DOI: 10.1037/bul0000031] [Citation(s) in RCA: 232] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A fundamental issue in cognitive neuroscience is how the brain encodes others' actions and intentions. In recent years, a potential advance in our knowledge on this issue is the discovery of mirror neurons in the motor cortex of the nonhuman primate. These neurons fire to both execution and observation of specific types of actions. Researchers use this evidence to fuel investigations of a human mirror system, suggesting a common neural code for perceptual and motor processes. Among the methods used for inferring mirror system activity in humans are changes in a particular frequency band in the electroencephalogram (EEG) called the mu rhythm. Mu frequency appears to decrease in amplitude (reflecting cortical activity) during both action execution and action observation. The current meta-analysis reviewed 85 studies (1,707 participants) of mu that infer human mirror system activity. Results demonstrated significant effect sizes for mu during execution (Cohen's d = 0.46, N = 701) as well as observation of action (Cohen's d = 0.31, N = 1,508), confirming a mirroring property in the EEG. A number of moderators were examined to determine the specificity of these effects. We frame these meta-analytic findings within the current discussion about the development and functions of a human mirror system, and conclude that changes in EEG mu activity provide a valid means for the study of human neural mirroring. Suggestions for improving the experimental and methodological approaches in using mu to study the human mirror system are offered.
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Affiliation(s)
- Nathan A Fox
- Department of Human Development and Quantitative Methodology, University of Maryland
| | | | - Kathryn H Yoo
- Department of Human Development and Quantitative Methodology, University of Maryland
| | - Lindsay C Bowman
- Department of Human Development and Quantitative Methodology, University of Maryland
| | - Erin N Cannon
- Department of Human Development and Quantitative Methodology, University of Maryland
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Abstract
The activity of mirror neurons in macaque ventral premotor cortex (PMv) and primary motor cortex (M1) is modulated by the observation of another's movements. This modulation could underpin well documented changes in EEG/MEG activity indicating the existence of a mirror neuron system in humans. Because the local field potential (LFP) represents an important link between macaque single neuron and human noninvasive studies, we focused on mirror properties of intracortical LFPs recorded in the PMv and M1 hand regions in two macaques while they reached, grasped and held different objects, or observed the same actions performed by an experimenter. Upper limb EMGs were recorded to control for covert muscle activity during observation.The movement-related potential (MRP), investigated as intracortical low-frequency LFP activity (<9 Hz), was modulated in both M1 and PMv, not only during action execution but also during action observation. Moreover, the temporal LFP modulations during execution and observation were highly correlated in both cortical areas. Beta power in both PMv and M1 was clearly modulated in both conditions. Although the MRP was detected only during dynamic periods of the task (reach/grasp/release), beta decreased during dynamic and increased during static periods (hold).Comparison of LFPs for different grasps provided evidence for partially nonoverlapping networks being active during execution and observation, which might be related to different inputs to motor areas during these conditions. We found substantial information about grasp in the MRP corroborating its suitability for brain-machine interfaces, although information about grasp was generally low during action observation.
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Wamain Y, Pluciennicka E, Kalénine S. Temporal dynamics of action perception: Differences on ERP evoked by object-related and non-object-related actions. Neuropsychologia 2014; 63:249-58. [DOI: 10.1016/j.neuropsychologia.2014.08.034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Revised: 08/25/2014] [Accepted: 08/29/2014] [Indexed: 10/24/2022]
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Simpson EA, Murray L, Paukner A, Ferrari PF. The mirror neuron system as revealed through neonatal imitation: presence from birth, predictive power and evidence of plasticity. Philos Trans R Soc Lond B Biol Sci 2014; 369:20130289. [PMID: 24778381 PMCID: PMC4006187 DOI: 10.1098/rstb.2013.0289] [Citation(s) in RCA: 90] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
There is strong evidence that neonates imitate previously unseen behaviours. These behaviours are predominantly used in social interactions, demonstrating neonates' ability and motivation to engage with others. Research on neonatal imitation can provide a wealth of information about the early mirror neuron system (MNS), namely its functional characteristics, its plasticity from birth and its relation to skills later in development. Although numerous studies document the existence of neonatal imitation in the laboratory, little is known about its natural occurrence during parent-infant interactions and its plasticity as a consequence of experience. We review these critical aspects of imitation, which we argue are necessary for understanding the early action-perception system. We address common criticisms and misunderstandings about neonatal imitation and discuss methodological differences among studies. Recent work reveals that individual differences in neonatal imitation positively correlate with later social, cognitive and motor development. We propose that such variation in neonatal imitation could reflect important individual differences of the MNS. Although postnatal experience is not necessary for imitation, we present evidence that neonatal imitation is influenced by experience in the first week of life.
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Affiliation(s)
- Elizabeth A. Simpson
- Department of Neuroscience, University of Parma, Parma 43215, Italy
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, Poolesville, MD 20837, USA
| | - Lynne Murray
- School of Psychology and Clinical Language Sciences, University of Reading, Reading RG6 7BE, UK
- Department of Psychology, Stellenbosch University, Stellenbosch 7600, South Africa
| | - Annika Paukner
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, Poolesville, MD 20837, USA
| | - Pier F. Ferrari
- Department of Neuroscience, University of Parma, Parma 43215, Italy
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Cooper NR, Simpson A, Till A, Simmons K, Puzzo I. Beta event-related desynchronization as an index of individual differences in processing human facial expression: further investigations of autistic traits in typically developing adults. Front Hum Neurosci 2013; 7:159. [PMID: 23630489 PMCID: PMC3635089 DOI: 10.3389/fnhum.2013.00159] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 04/10/2013] [Indexed: 11/13/2022] Open
Abstract
The human mirror neuron system (hMNS) has been associated with various forms of social cognition and affective processing including vicarious experience. It has also been proposed that a faulty hMNS may underlie some of the deficits seen in the autism spectrum disorders (ASDs). In the present study we set out to investigate whether emotional facial expressions could modulate a putative EEG index of hMNS activation (mu suppression) and if so, would this differ according to the individual level of autistic traits [high versus low Autism Spectrum Quotient (AQ) score]. Participants were presented with 3 s films of actors opening and closing their hands (classic hMNS mu-suppression protocol) while simultaneously wearing happy, angry, or neutral expressions. Mu-suppression was measured in the alpha and low beta bands. The low AQ group displayed greater low beta event-related desynchronization (ERD) to both angry and neutral expressions. The high AQ group displayed greater low beta ERD to angry than to happy expressions. There was also significantly more low beta ERD to happy faces for the low than for the high AQ group. In conclusion, an interesting interaction between AQ group and emotional expression revealed that hMNS activation can be modulated by emotional facial expressions and that this is differentiated according to individual differences in the level of autistic traits. The EEG index of hMNS activation (mu suppression) seems to be a sensitive measure of the variability in facial processing in typically developing individuals with high and low self-reported traits of autism.
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Affiliation(s)
- Nicholas R Cooper
- Centre for Brain Science, Department of Psychology, University of Essex Colchester, UK
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Silas J, Levy JP, Holmes A. Sensitivity of 'mu' rhythm modulation to the relevance of an observed movement but not to goal congruency. Int J Psychophysiol 2012; 85:168-73. [PMID: 22664307 DOI: 10.1016/j.ijpsycho.2012.05.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 05/03/2012] [Accepted: 05/27/2012] [Indexed: 11/29/2022]
Abstract
There is some dispute over whether the primary role of a system that processes both performed and observed actions (the mirror neuron system) is action understanding or the coordination of action with others. We present behavioural and EEG data from a motor priming task that shed some light on this debate. Participants are asked to make one of two simple actions whilst watching video clips of movements that differ in terms of their visuospatial overlap with, and goal-related relevance to, the required performed action. The reaction time data appear to support a direct matching account where visuospatial overlap is prioritised over relevance. However, the EEG data appear to reflect a system that is sensitive to the relevance of the observed movement and suggest an action prediction role for a mirror neuron system.
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Hofelich AJ, Preston SD. The meaning in empathy: distinguishing conceptual encoding from facial mimicry, trait empathy, and attention to emotion. Cogn Emot 2011; 26:119-28. [PMID: 21500047 DOI: 10.1080/02699931.2011.559192] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In order to truly empathise with another, we need to recognise and understand how they feel. Perception-action models of empathy predict that attending to another's emotion will spontaneously activate the observer's own conceptual knowledge for the state, but it is unclear how this activation is related to facial mimicry, trait empathy, or attention to emotion more generally. In the current study, participants did spontaneously encode background facial expressions at a conceptual level even though they were irrelevant to the task (the Emostroop effect; Preston & Stansfield, 2008), but this encoding was not associated with mimicry of the faces, trait empathy, the ability to resolve competing semantic representations (Colour-naming Stroop task), or the tendency to be distracted by emotional information more generally (Intrusive Cognitions task). Our results suggest that trait empathy increases attention to emotional information, but conceptual encoding occurs across individuals as a natural consequence of attended perception.
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Affiliation(s)
- Alicia J Hofelich
- Department of Psychology, University of Michigan, Ann Arbor, MI 48109, USA.
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Lee TW, Yu YWY, Hong CJ, Tsai SJ, Wu HC, Chen TJ. The influence of serotonin transporter polymorphisms on cortical activity: a resting EEG study. BMC Neurosci 2011; 12:33. [PMID: 21507249 PMCID: PMC3110125 DOI: 10.1186/1471-2202-12-33] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Accepted: 04/20/2011] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The serotonin transporter gene (5-HTT) is a key regulator of serotonergic neurotransmission and has been linked to various psychiatric disorders. Among the genetic variants, polymorphisms in the 5-HTT gene-linked polymorphic region (5-HTTLPR) and variable-number-of-tandem-repeat in the second intron (5-HTTVNTR) have functional consequences. However, their genetic impact on cortical oscillation remains unclear. This study examined the modulatory effects of 5-HTTLPR (L-allele carriers vs. non-carriers) and 5-HTTVNTR (10-repeat allele carriers vs. non-carriers) polymorphism on regional neural activity in a young female population. METHODS Blood samples and resting state eyes-closed electroencephalography (EEG) signals were collected from 195 healthy women and stratified into 2 sets of comparisons of 2 groups each: L-allele carriers (N=91) vs. non-carriers for 5-HTTLPR and 10-repeat allele carriers (N=25) vs. non-carriers for 5-HTTVNTR. The mean power of 18 electrodes across theta, alpha, beta, gamma, gamma1, and gamma2 frequencies was analyzed. Between-group statistics were performed by an independent t-test, and global trends of regional power were quantified by non-parametric analyses. RESULTS Among 5-HTTVNTR genotypes, 10-repeat allele carriers showed significantly low regional power at gamma frequencies across the brain. We noticed a consistent global trend that carriers with low transcription efficiency of 5-HTT possessed low regional powers, regardless of frequency bands. The non-parametric analyses confirmed this observation, with P values of 3.071×10-8 and 1.459×10-12 for 5-HTTLPR and 5-HTTVNTR, respectively. CONCLUSIONS AND LIMITATIONS Our analyses showed that genotypes with low 5-HTT activity are associated with less local neural synchronization during relaxation. The implication with respect to genetic vulnerability of 5-HTT across a broad range of psychiatric disorders is discussed. Given the low frequency of 10-repeat allele of 5-HTTVNTR in our research sample, the possibility of false positive findings should also be considered.
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Affiliation(s)
- Tien-Wen Lee
- Department of Psychiatry, Chang Gung Memorial Hospital, and College of Medicine, Chang Gung University, Taoyuan County, Taiwan
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