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.

Assessing human mirror activity with EEG Mu Rhythm: a meta-analysis

Estimates of functional connectivity derived from resting-state functional magnetic resonance imaging (rs-fMRI) are highly sensitive to artefacts caused by in-scanner head motion. This susceptibility has motivated the development of numerous denoising methods designed to mitigate motion-related artefacts. Here, we compare 8 popular retrospective rs-fMRI denoising methods, including methods such as regression of head motion parameters (with or without expansion terms), aCompCor, volume censoring (e.g., scrubbing and spike regression), global signal regression and ICA-AROMA, combined into 16 different pipelines. These pipelines were evaluated across five different quality control benchmarks in three independent datasets that were characterized by both high and low levels of motion. Pipelines were benchmarked by examining the residual relationship between in-scanner movement and functional connectivity after denoising; the effect of distance on this residual relationship; whole-brain differences in functional connectivity between high- and low-motion healthy controls (HC); the temporal degrees of freedom lost during denoising; and the test-retest reliability of functional connectivity estimates. We also compared the sensitivity of each pipeline to clinical differences in functional connectivity in comparisons between people with schizophrenia (SCZ; n = 50) and HCs (n = 121) and people with obsessive-compulsive disorder (OCD; n = 34) and HCs (n = 39). Our results indicate that (1) simple linear regression of regional fMRI time series against head motion parameters (with or without expansion terms) is not sufficient to remove head motion artefacts; (2) aCompCor pipelines can exacerbate motion artefacts in low-motion data; (3) the primary benefit of volume censoring comes from the exclusion of high-motion individuals rather than censoring of data in remaining participants; and (4) that ICA-AROMA consistently performed well across all benchmarks and datasets, particularly when applied after the exclusion of high-motion individuals. ICA-AROMA was also the most sensitive to clinical differences in case-control analyses, suggesting that its denoising efficacy is associated with enhanced power for detecting pathophysiological effects. Crucially, the comparison between HC and SCZ revealed that the specific choice of noise correction pipeline had a major effect on the findings, affecting both the location and direction of group differences. Putative increases in functional connectivity in patients only emerged in pipelines incorporating either global signal regression or aCompCor. Thus, group comparisons in functional connectivity are highly dependent on preprocessing strategy. We offer some recommendations for best practice and outline some simple analyses to facilitate transparent reporting of the degree to which a given set of findings may be affected by motion-related artefact.

https://www.biorxiv.org/content/biorxiv/early/2017/06/27/156380.full.pdf

An evaluation of the efficacy, reliability, and sensitivity of motion correction strategies for resting-state functional MRI

Mu suppression – a good measure of the human mirror neuron system?

It is typically assumed that perception for action and object recognition are subserved by functionally and neuroanatomically distinct processing streams in the brain However, recent evidence challenges this classical view and suggests an interaction between both visual processing streams While previous studies showed an influence of object perception on action-related tasks, we investigated whether action representations facilitate visual object recognition In order to address this question, two briefly displayed masked objects were sequentially presented, either affording congruent or incongruent motor interactions We found superior naming accuracy for object pairs with congruent as compared to incongruent motor interactions (Experiment 1) This action priming effect indicates that action representations can facilitate object recognition We further investigated the nature of the representations underlying this action priming effect The effect was absent when the prime stimulus was presented as a word (Experiment 2) Thus, the action priming effect seems to rely on action representations specified by visual object information Our findings suggest that processes of object-directed action influence object recognition

The role of action representations in visual object recognition

Do mirror neuron areas mediate mu rhythm suppression during imitation and action observation

We examined the effect of hand grip on object recognition by studying the modulation of the mu rhythm when participants made object decisions to objects and non-objects shown with congruent or incongruent hand-grip actions. Despite the grip responses being irrelevant to the task, mu rhythm activity on the scalp over motor and pre-motor cortex was sensitive to the congruency of the hand grip – in particular the event related desynchronization of the mu rhythm was more pronounced for familiar objects grasped with an appropriate grip than for objects given an inappropriate grasp. Also the power of mu activity correlated with RTs to congruently gripped objects. The results suggest that familiar motor responses evoked by the appropriateness of a hand grip facilitate recognition responses to objects.

/pdf/mu-rhythm-desynchronization-reveals-motoric-influences-of-362ujsbsha.pdf

Margaret Jane Riddoch

Papers

Mu rhythm desynchronization reveals motoric influences of hand action on object recognition.