The interpretation of mu suppression as an index of mirror neuron activity: past, present and future

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

Attention modulates motor system activation during action observation: evidence for inhibitory rebound

Perceiving another individual’s actions activates the human motor system. We investigated whether this effect is stronger when the observed action is relevant to the observer’s task. The mu rhythm (oscillatory activity in the 8- to 13-Hz band over sensorimotor cortex) was measured while participants watched videos of grasping movements. In one of two conditions, the participants had to later report how many times they had seen a certain kind of grasp. In the other condition, they viewed the identical videos but had to later report how many times they had seen a certain colour change. The colour change and the grasp always occurred simultaneously. Results show mu rhythm attenuation when watching the videos relative to baseline. This attenuation was stronger when participants later reported the grasp rather than the colour, suggesting that the motor system is more strongly activated when the observed grasping actions were relevant to the observer’s task. Moreover, when the graspable object disappeared after the offset of the video, there was subsequent mu rhythm enhancement, reflecting a post-stimulus inhibitory rebound. This enhancement was again stronger when making judgments about the grasp than the colour, suggesting that the stronger activation is followed by a stronger inhibitory rebound

Investigating the effects of neuromodulatory training on autistic traits: a multi-methods psychophysiological study.

Autism spectrum disorder (ASD) is characterized by noticeable difficulties with social interaction and communication. Building on past research in this area and with the aim of improving methodological perspectives, a multi method approach to the study of ASD, mirror neurons and neurofeedback was taken. This thesis is made up of three main experiments: 1) A descriptive study of the resting state electroencephalography (EEG) across the spectrum of autistic traits in neurotypical individuals, 2) A comparison of 3 EEG protocols on MNs activation (mu suppression) and its difference according to self-reported traits of autism in neurotypical individuals, and 3) Neurofeedback training (NFT) on individuals with high autistic traits. In chapters 3 and 4 we employed simultaneous monitoring of physiological data. For chapter 3 EEG and eye-tracking was used, In the case of chapter 4, EEG and eye-tracking as well functional near infrared spectroscopy (fNIRS). Overall the findings revealed differences in mu rhythm reactivity associated to AQ traits. In chapter 2, the rEEG showed that individuals with high AQ scores showed less activation of frontal and fronto-central regions combined with higher levels of complexity in fronto-temporal, temporal, parietal and parieto-occipital areas. In chapter 3, EEG protocols that elicited Mu reactivity in individuals with different AQ traits suggested that as the AQ traits become more pronounced in neurotypical population, the event-related desynchronization (ERD) in low alpha declines. Chapter 3 was also the basis for the choice of pre/post assessment for chapter 4. In chapter 4 the multi-method physiological approach provided parallel physiological evidence for the effects of NFT in sensorimotor reactivity, namely, an increase in ERD in high alpha, higher levels of oxygenated haemoglobin and changes to the amplitude and frequency in the microstructure of mu for participants who underwent active training as opposed to a sham group

Through a Mirror Darkly: Shedding Light on Individual Differences in the Neural Correlates of Empathy

The aim of this thesis was to explore individual differences in the neural correlates of empathy. This was achieved over the course of three experimental studies to gain a better understanding of mirror neuron activity as a putative index of empathy and its relationship with self-report measures of empathy. In the first study we built upon the existing literature by exposing participants to two EEG protocols. Findings demonstrated a more reactive mirror neuron system in response to crying relative to laughing sounds and to painful relative to non-painful imagery. We also found inverse relationships with empathy that could be related to expertise. In our second study we examined the long-term effect of loving-kindness meditation (compared to controls) on empathy by comparing the mirror neuron activity from three EEG protocols. It is argued that we found meaningful differences in mirror neuron activity (for each protocol) that might again be explained by an expertise effect. The final study investigated the potential effect of power-posing on empathy as measured by both EEG and behavioural tasks. Findings demonstrated that those in an open pose (counter to predictions) actually performed better on an empathic accuracy task than those in a closed or control posture. In terms of mirror neuron activity, we find no conclusive evidence to suggest that open posing has a negative effect on empathy, however again we see evidence to suggest that expertise might be driving our data

La représentation auditive motrice reflétée par la négativité de discordance chez l’enfant présentant un trouble du spectre de l’autisme

Il est maintenant bien établi que le cerveau humain est doté d’un système de neurones qui s’active tant à la perception qu’à l’exécution d’une action. Les neurones miroirs, ainsi que le système qu’ils forment avec des structures adjacentes appelées système neurones miroirs (SNM), ont été relié à la compréhension d’action et pourrait être impliqué dans les fonctions sociales de haut niveau tel que l’empathie et l’imitation. Dans la foulée spéculative reliant le SNM à la sphère sociale, le dysfonctionnement de ce système a rapidement gagné intérêt dans la genèse des anomalies du domaine social chez les personnes présentant le Trouble du spectre de l’autisme (TSA). Néanmoins, l’hypothèse voulant que le dysfonctionnement social des TSA repose sur une atteinte du SNM est controversée. En effet, les études soutenant cette hypothèse nécessitent des fonctions cognitives et sociales qui peuvent contribuer à l’obtention de résultats atypiques, telles que la compréhension des consignes, l’attention sur des stimuli sociaux ou la réalisation d’acte moteur. Récemment, un protocole auditif de négativité de discordance (MMN) utilisant des stimuli reliés à l’action humaine a été utilisé pour mesurer l’activité du SNM. Cette technique semble prometteuse dans la mesure où elle ne nécessite pas de capacités attentionnelles ou langagières, elle est brève et demande un montage minimal d’électrodes. Le premier article avait comme objectif principal de mesurer la validité de convergence du protocole MMN relié à l’action avec celui du rythme mu, le protocole le plus utilisé pour enregistrer l’activité miroir à l’aide de l’électroencéphalographie (EEG). Les modes de stimulation ont été délivrées en bloc successif à un groupe de 12 adultes en santé. Alors que les deux techniques ont modulé efficacement les régions fronto-centrales et centrales respectivement, mais ne sont pas corrélées, nous avons conclu qu’il est possible 2 qu’elles mesurent des aspects différents du SNM. Le deuxième article avait comme objectif principal de mesurer l’activité du SNM à l’aide du protocole MMN relié à l’action chez 10 enfants présentant un TSA ainsi que chez 12 enfants neurotypiques dans la même tranche d’âge (5-7ans). Chez les enfants TSA, nous avons montré un patron de latence inversée, comparativement aux enfants du groupe contrôle; ils traitaient plus rapidement les sons contrôles que les sons reliés à l’action humaine, alors que la tendance inverse était observée chez les contrôles. De plus, bien que les deux groupes différaient quant aux sons d’action, ils ne différaient pas quant aux sons contrôles. Quant à l’amplitude, les enfants TSA se distinguaient du groupe contrôle par une amplitude restreinte du son d’action provenant de la bouche. Par ailleurs, les mesures neurophysiologiques et neuropsychologiques n’étaient pas corrélées. En sommes, basé sur la prémisse que ce protocole MMN pourrait mesurer l’activité du SNM, cette thèse a comme but d’améliorer les connaissances quant à son utilisation chez l’adulte et l’enfant neurotypique ainsi que chez l’enfant TSA. Celui-ci pourrait ultimement être utilisé comme un biomarqueur potentiel du TSA.Mirror-neuron system (NMS) has been suggested to underlie action understanding, which is believed to be involved in higher social functions such as empathy and imitation. Numerous studies have also provided indirect evidence supporting the existence of a MNS in the human brain using functional magnetic resonance imaging, transcranial magnetic stimulation, magnetoenceophalography and electroencephalography (EEG). As evidence relating MNS function with social cognition accumulated, its dysfunction was proposed to underlie social impairments in Autism Spectrum Disorder (ASD). Although some studies have reported structural and/or functional data supporting this hypothesis, it remains controversial. Indeed, the techniques used to probe MNS activity often require the participant to understand the task, display sustained attention and present spared visual cognitive functions, which could be altered in ASD population. This, in turn, could partly explain differences in MNS activity found between invididuals with ASD and neurotypical participants. The auditory mismatch negativity (MMN) protocol has recently been proposed as a viable tool to assess MNS activity using action-related sounds. This relatively short oddball paradigm does not require visual, attentional or language skills and can be performed with minimal electrode installation (minimal use of 4 electrodes). This action-related MMN may therefore be well-suited to investigate MNS function in very young children or populations with mental disabilities, such as ASD. The first article of this thesis assessed the convergent validity of the action-related MMN protocol with a mu rhythm suppression paradigm, which is the most commonly used EEG measure of MNS activity. To do so, both protocols were consecutively administered in healthy adults in the same experimental session. While both techniques successfully 4 modulated the fronto-central and central brain regions using action-related stimuli, they did not correlate significantly. This suggests that the two techniques may not probe the same aspects of MNS function. The second article aimed at investigating MNS activity in children with ASD using the action-related MMN protocol. Data were compared to age-matched typically developing children. We show that children with ASD present an opposite pattern to that of control children : whereas MMN latencies are shorter for action-related sounds compared to control sounds in neurotypical children, the opposite pattern is observed in children with ASD. Furthermore, although the two groups present different response patterns with regards to action-related sounds, they repond similarly to control sounds. For amplitude measurements, children with ASD display reduced amplitude to action-related sounds produced by the mouth compared to neurotypical children. In summary, this thesis aimed at determining whether and action-related MMN protocol could be used to measure MNS activity in neurotypical adults and children, as well as in ASD children. The action-related MMN could potentially be used as a biological biomarker of ASD pending further studies

Neural empathy mechanisms are shared for physical and social pain, and increase from adolescence to older adulthood

Empathy is a critical component of social interaction that enables individuals to understand and share the emotions of others. We report a pre-registered experiment in which 240 participants, including adolescents, young adults and older adults, viewed images depicting hands and feet in physically or socially painful situations (vs. non-painful). Empathy was measured using imagined pain ratings and EEG mu suppression. Imagined pain was greater for physical vs. social pain, with young adults showing particular sensitivity to social pain events compared to adolescents and older adults. Mu desynchronisation was greater to pain vs. no-pain situations, but the physical/social context did not modulate pain responses. Brain responses to painful situations increased linearly from adolescence to young and older adulthood. These findings highlight shared activity across the core empathy network for both physical and social pain contexts, and an empathic response that develops over the lifespan with accumulating social experience

Motor imagery during action observation enhances automatic imitation in children with and without developmental coordination disorder

Developmental coordination disorder (DCD) is a neurodevelopmental condition characterized by uncoordinated movement relative to age. While action observation (AO) and motor imagery (MI) can both independently enhance movement skills in children, we report the first study to assess the effects of combined action observation and motor imagery (AO + MI) on automatic imitation in children aged 7–12 years both with DCD (n = 12) and without DCD (n = 12). On each trial, participants planned to execute an instructed rhythmical action (face washing or paint brushing). Before responding, participants observed a rhythmical distractor showing the same or a different action with a subtle speed manipulation across trials (fast vs. slow). Automatic imitation was quantified as an imitation bias in subsequent response cycle times. Across blocks of trials, participants engaged in AO, MI, or combined AO + MI during the distractor phase or intentionally imitated the distractor speeds. Although there were no between groups differences, combined AO + MI instructions produced a significantly greater imitation bias (115%) than both AO (109%) and MI (109%), with intentional imitation yielding the strongest effects overall (128%). Within groups analyses revealed a significant bias for AO and MI in both groups. Combined AO + MI effects were significantly greater than AO in typically developing children and were greater than both AO and MI in children with DCD. These results demonstrate a clear capacity for different forms of motor simulation in children both with and without DCD. Moreover, combined AO + MI instructions represent an advantageous method for training movements in children with different motor abilities compared with separate AO and MI instructions.</p

The development of social processing in young children: insights from somatosensory activations during observation and experience of touch in typically developing children and speech processing in children with autism spectrum disorders

This thesis explores the neural mechanisms underlying the observation of touch and tactile processing in adults and typically developing children and speech versus computerized speech processing in children with autism spectrum disorders (ASD). Chapter 1 reviews the literature on mirror functioning, embodied cognition and typical and atypical development of social and speech processing in infancy and childhood. Chapter 2 investigates the neural mechanisms underlying hand and object touch observation in adults. In Chapter 3, a similar procedure is employed to investigate tactile mirroring mechanisms in children. The findings demonstrate that these mechanisms are relatively developed in 4- to 5- year old children. Chapter 4 further explores somatosensory activity during touch in adults and children. The findings reveal the modulation of somatosensory beta (15-24 Hz) activity during touch in adults, but not in children. Chapter 5 examines the neural mechanisms underlying speech versus computerized speech perception in children with ASD. These results suggest an impaired classification of speech sounds preceded by computerized speech, and atypical lateralization of speech processing in children with ASD. Together, these findings make a notable contribution to our understanding of typical development of tactile mirroring and touch processing mechanisms, and social processing dysfunctions in children with ASD