PAPER Relations between infants’ emerging reach-grasp competence and event-related desynchronization in EEG Erin N. Cannon, 1 Elizabeth A. Simpson, 2,3 Nathan A. Fox, 1 Ross E. Vanderwert, 4 Amanda L. Woodward 5 and Pier F. Ferrari 2 1. Department of Human Development and Quantitative Methodology, University of Maryland, USA 2. Dipartimento di Neuroscienze, Universit a di Parma, Italy 3. Eunice Kennedy Shriver National Institutes of Child Health and Human Development, Poolesville, USA 4. Laboratories of Cognitive Neuroscience, Division of Developmental Medicine, Children’s Hospital Boston, USA 5. Department of Psychology, University of Chicago, USA Abstract Recent reports of similar patterns of brain electrical activity (electroencephalogram: EEG) during action execution and observation, recorded from scalp locations over motor-related regions in infants and adults, have raised the possibility that two foundational abilities – controlling one’s own intentional actions and perceiving others’ actions – may be integrally related during ontogeny. However, to our knowledge, there are no published reports of the relations between developments in motor skill (i.e. recording actual motor skill performance) and EEG during both action execution and action observation. In the present study we collected EEG from 21 9-month-olds who were given opportunities to reach for toys and who also observed an experimenter reach for toys. Event-related desynchronization (ERD) was computed from the EEG during the reaching events. We assessed infants’ reaching-grasping competence, including reach latency, errors, preshaping of the hand, and bimanual reaches, and found that desynchronization recorded in scalp electrodes over motor-related regions during action observation was associated with action competence during execution. Infants who were more competent reachers, compared to less competent reachers, exhibited greater ERD while observing reaching-grasping. These results provide initial evidence for an early emerging neural system integrating one’s own actions with the perception of others’ actions. Research highlights • The control of intentional actions and the meaningful perception of others’ actions are integrally related during ontogeny. • A neural mirror system predicts that developments in infants’ motor competence should be associated with the strength of EEG mu desynchronization during action observation. • To explore this, 9-month-old infants reached for toys and observed an experimenter reaching for toys while we recorded EEG activity in the mu frequency band. • We found that greater desynchronization in scalp electrodes located over motor-related regions during action observation was associated with greater reach- ing-grasping competence, suggesting an early emerg- ing neural system integrating one’s own actions with the perception of others’ actions. Introduction The notion that two foundational abilities – the control of one’s own intentional actions and the meaningful perception of others’ actions – are integrally related has gained momentum and opened debate in behavioral and neuroscience fields in recent years. The mu rhythm, an electroencephalogram (EEG) rhythm found over senso- rimotor areas of the scalp, has been associated with both motor behavior and the perception of biological move- Address for correspondence: Erin Cannon, Department of Human Development and Quantitative Methodology, University of Maryland, College Park, MD 20742, USA; e-mail: ecannon@umd.edu © 2015 John Wiley & Sons Ltd Developmental Science (2015), pp 1–13 DOI: 10.1111/desc.12295