Mu Rhythm Suppression Reflects Mother-Child Face-to-Face Interactions: A Hyperscanning MEG Study

Background:

Spontaneous face-to-face interactions between mothers and their children play crucial roles in the development of social minds. However, these inter-brain dynamics are still unclear. To better understand the inter-brain dynamics that occur during human interactions, it is necessary to research not only a single brain in isolation but two brains during a real interaction. Simultaneous multiple brain functional measurements may reveal the brain dynamics underlying social interactions.

Objectives:

We measured the mu suppression during face-to-face spontaneous nonverbal interactions between mothers and their children with autism spectrum disorder (ASD) using the dual magnetoencephalography (MEG) system.

Methods:

Fourteen children with ASD and their mothers participated in this experiment. They were diagnosed by a clinical psychiatrist and a clinical psychologist with more than 5 years of experience in ASD using the Autism Diagnostic Observational Schedule–Generic (ADOS), the Diagnostic Interview for Social and Communication Disorders (DISCO), and the DSM-5 criteria at the time that they entered into this study. We used a 160 channel MEG (MEG vision NEO, Yokogawa Electric Corporation) and a 151 channel MEG (PQ1151R, Yokogawa Electric Corporation/KIT). These MEG systems were housed in a magnetically shielded room. To measure the mother-child interactions in a face-to-face situation, we set up a real-time dual video presentation to show the facial expressions of the mother and child. Short movies and the other’s facial expression with a live movie or a still picture were alternately displayed for 10 or 15 sec, respectively, on the half-mirror screen, while simultaneous, neuromagnetic recordings of their brain activities were performed.

Results:

The results demonstrated significant correlations between the index of mu suppression (IMS) in the right precentral area and the traits of ASD in 13 mothers and 8 children (Data from some children and a mother could not be obtained due to artifacts). In addition, higher IMS values (i.e., strong mu suppression) in mothers were associated with higher IMS values in their children. To evaluate the behavioral contingency between mothers and their children, we calculated cross correlations between the magnitude of the mother and child head-motion during MEG recordings. As a result, in mothers whose head motions tended to follow her child’s head motion, the magnitudes of mu suppression in the mother’s precentral area were large.

Conclusions:

Our results from this study demonstrated that the mu suppression level of ASD children and their mothers reflects their social ability or autistic traits and demonstrated a correlation between the mu suppression in the mothers and their children. Further studies with larger sample sizes, including both typically developing children and children with ASD, are necessary to test the reliability of these findings and support their generalization to interactions between typically developed mothers and typically developing children.