Mirroring Activity During Observation of Actions Underlies Distinct yet Functionally Connected Motor and Attention Processes

• In Event: 2-128 - Function and Development of the Mirror System in Infancy and Toddlerhood

Integrative Statement

The mirroring system is believed to be involved in infant’s social-cognitive development such as, imitation, language, motor skill learning. The EEG mu rhythm (oscillation in the alpha (6-9Hz in infant) frequency range) a putative measure of the mirroring system, reflects motor cortex activation, and has been found to be desynchronized during both action execution and observation. As such, modulation of the mu rhythm has become widely used as a marker of mirroring system activity in humans, however concerns over its validity as such have recently been raised. One significant concern is the contamination of mu rhythm and visual alpha (Hobson and Bishop, 2016). This issue may be particularly problematic in studies utilizing the mu rhythm as the measure of mirroring activity in developmental populations, as children and infants are likely to exhibit greater attention to others' actions as they learn about objects, actions, and the goals and intentions driving actions (Bowman et al., 2017). The goal of the present study was to address this concern by examining the proposal that the mu rhythm over central cortical regions is distinct from yet functionally connected to alpha activity over the occipital region during observation of actions in infancy.
To do so, we employed high density EEG recording and performed a comprehensive analysis of the EEG data, which included: time-frequency decomposition in mu/alpha (6-9Hz) frequency range, scalp topographies and functional connectivity between brain areas in 6-9Hz frequency range. EEG was recorded while 46 9-month-old infants executed grasping actions and observed an experimenter grasping. To address the concern regarding contamination of mu rhythm and alpha activity, the EEG data were transformed via surface Laplacian into a reference free current source density (CSD) waveform, which minimizes the effect of volume conduction thus improving both spatial and functional specificity of mu and alpha activity. Moreover, we calculated a measure of phase-connectivity, which indicates a mechanism for functionally coupled interregional activity to provide insight regarding potential functional connectivity between mirroring and attention processes.
Mu desynchronization was evident over central regions during both execution and observation of movements (Figure 1), and independent alpha desynchronization over occipital region was also present in both conditions. The connectivity analyses revealed that central-occipital areas were functionally more connected compared to other areas of the brain during observation of movements (Figure 2). Collectively, the results demonstrate that while these two areas of activity (motor and visual systems) are distinct they may also work in concert. Overall these findings provide significant information about the mu rhythm and its validity as a measure of mirroring system activity in human and support the proposal of a functional connection between distinct motor and attention processes during observation of action.

Authors

• Ranjan Debnath, University of Maryland, College Park
  Presenting Author

• Virginia Salo, University of Maryland, College Park
  Non-Presenting Author

• George A Buzzell, University of Maryland, College Park
  Non-Presenting Author

• Kathryn H Yoo, University of California, Davis
  Non-Presenting Author

• Nathan Fox, University of Maryland
  Non-Presenting Author