This article argues that mirror neurons originate in sensorimotor associative learning and therefore a new approach is needed to investigate their functions. Mirror neurons were discovered about 20 years ago in the monkey brain, and there is now evidence that they are also present in the human brain. The intriguing feature of many mirror neurons is that they fire not only when the animal is performing an action, such as grasping an object using a power grip, but also when the animal passively observes a similar action performed by another agent. It is widely believed that mirror neurons are a genetic adaptation for action understanding; that they were designed by evolution to fulfill a specific socio-cognitive function. In contrast, we argue that mirror neurons are forged by domain-general processes of associative learning in the course of individual development, and, although they may have psychological functions, they do not necessarily have a specific evolutionary purpose or adaptive function. The evidence supporting this view shows that (1) mirror neurons do not consistently encode action "goals"; (2) the contingency- and context-sensitive nature of associative learning explains the full range of mirror neuron properties; (3) human infants receive enough sensorimotor experience to support associative learning of mirror neurons ("wealth of the stimulus"); and (4) mirror neurons can be changed in radical ways by sensorimotor training. The associative account implies that reliable information about the function of mirror neurons can be obtained only by research based on developmental history, system-level theory, and careful experimentation.

/pdf/mirror-neurons-from-origin-to-function-2cikufi2n0.pdf

Mirror neurons: from origin to function

Our understanding of the functions of motor system evolved remarkably in the last 20 years. This is the consequence not only of an increase in the amount of data on this system but especially of a ...

Cortical Mechanisms Underlying the Organization of Goal-Directed Actions and Mirror Neuron-Based Action Understanding

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

http://ilabs.washington.edu/meltzoff/pdf/11MarshallMeltzoff_Mirroring_DCN.pdf

Neural Mirroring Systems: Exploring the EEG Mu Rhythm in Human Infancy

How do infants understand the goals of others' actions? It has been proposed that action-understanding results from a mechanism whereby an observed action is mapped onto the observer's own motor representation of that action. However, direct evidence of the matching process in early infancy is difficult to find. Here we show the developmental correspondence between action prediction and motor ability by comparing gazing and grasping responses to interesting objects in 4- to 10-month-old infants and adults. The onset of infants' ability to predict the goal of others' action was found to be synchronized with the onset of their own ability to perform that action. Moreover, there was correspondence relationship between action-prediction ability and motor ability of same action. Our findings indicate that the ability to predict others' action goals requires a corresponding motor ability, providing ontogenetic evidence for a direct matching process by a mirror neuron system.

/pdf/developmental-correspondence-between-action-prediction-and-37tmo68wd5.pdf

Developmental correspondence between action prediction and motor ability in early infancy

The Mirror Neuron System hypothesis stating that observed actions are projected onto the observer’s own action system assigns an important role to development, because only actions mastered by the observer can be mirrored. The purpose of the present study was to investigate whether there is evidence of a functioning mirror neuron system (MNS) in 8-month-old infants. High-density EEG was used to assess the mu rhythm desynchronization in an action observation task where the infants observed a live model. To reduce noise, ICA decompositions were used. The results show a higher desynchronization of the mu rhythm when infants observed a goal-directed action than when they observed a spatially similar non-goal-directed movement. The localizations of the sources are in agreement with those proposed by the MNS hypothesis. This indicates that the MNS is functioning at this age.

Using mu rhythm desynchronization to measure mirror neuron activity in infants

The introduction of high density EEG (hd-EEG) nets for easy application on subjects of all ages has improved the possibilities to investigate the development of the infant neurophysiology This dissertation consists of three studies (I – III) that investigate the visual motion system and mirror neuron system of the infant, and methodological sections that outline the bioelectrical background and the characteristics of the methods used Study I covers the maturation of cortical areas involved in motion perception in adults and infants using an ERP paradigm Over three age groups (2, 3 and 5 month olds) the cortical activation increased dramatically All infant groups showed significant activation when moving displays was contrasted to static displays on a video screen The study shows that 5-month-old infants and older can be expected to process motion in a similar fashion as adultsStudy II covers the infant mirror neuron system (MNS) In adults the mu rhythm perturbations is considered a reliable measure of activation of the MNS This study presented both a mu rhythm analysis and a ERP analysis to detect MNS activity in 6-month-olds and in adults This study concludes that the infant MNS can be measured using ERPs and that the development of mu rhythm perturbations requires further studyStudy III focused on exploring the mu rhythm suppressions 8-month-olds observed a live actor that performed goal directed reaches and non-goal directed hand movements The results show robust mu rhythm perturbations time-locked to the grasping moment The study concluded that the MNS activity is possible to evaluate by analysis of mu rhythm perturbations and that the MNS show mature characteristics at the age of 8 monthsIn summary, Study 2 and 3 present new methods to investigate the infant mirror neuron system and shows that the infant MNS is active at 6 months of age At 8 months of age the infant MNS show mature EEG responses to simple actions such as reaching How the MNS development relates to the infants’ motor development, and how the MNS interacts with the development of social skills requires further studies that could benefit from the methods presented here

Therese Ljunghammar

Papers

Using mu rhythm desynchronization to measure mirror neuron activity in infants

Using mu rhythm perturbations to measure mirror neuron activity in infants