Toddler EEG power reflects behavioral social engagement state during naturalistic parent-child interaction.

Social engagement is a critical process for children's language and social development and is altered in neurodevelopmental conditions such as autism. Although previous EEG studies have investigated correlates of children's social development in closely controlled experimental studies, few studies have examined how the brain reflects meaningful behavioral states, such as social engagement, within naturalistic parent-child interaction. This study collected EEG from typically developing toddlers of varying language ability and their parent (n = 49, 24-44 months) during the Social EEG paradigm; dyads completed contexts of dyadic interaction (book reading and puzzle play) and baseline (movie watching) during EEG recording. Videos of the interaction session were coded for social engagement using moment-by-moment behavioral coding and applied to the EEG data. As predicted, child EEG alpha power decreased (p < .001) and theta power increased (p = .01) during social engagement relative to baseline movie engagement. Further, the same pattern was replicated in an independent sample (n = 24, 25-47 months) including children diagnosed with autism, who showed the same pattern of power. These results demonstrate for the first time that EEG power is associated with naturally occurring moments of parent-child social engagement across a range of social/linguistic abilities and ages. This opens avenues for study of more naturalistic and meaningful developmental constructs.