PROJECT SUMMARY The proposed work will adapt current wearable, optically pumped magnetometer-based magnetoencephalography (opmMEG) for use in infants, and will then further adapt these protocols for simultaneous recording of brain activity in mother-infant dyads during naturalistic social interactions. While both electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) have been used to assess brain function in infants, and EEG has even been used to simultaneously assess mother-infant dyad brain function during naturalistic interactions, they each have limitations that are addressed by wearable opmMEG. Both EEG and fMRI allow for high temporal, millisecond, resolution; however, EEG poses challenges for source localization. Although fMRI addresses the source localization issues of EEG, it does not allow for the same naturalistic social paradigms as EEG, and is also loud and expensive. OpmMEG is non-invasive, quiet, and provides both high temporal resolution and accurate source localization. OPMs can be used at room temperature, unlike other MEG sensors that must be cooled using expensive cryogens. OPMs are also small and lightweight, making them amenable to use in wearable helmets, which can be used even during paradigms that include participant motion. All of these characteristics of opmMEG make it an ideal candidate for adaptation for use in infants, and further, use in naturally interacting mother-infant dyads. The ability to assess brain function simultaneously within a mother-infant dyad represents an unprecedented opportunity to gain knowledge about typical development, which is key to being able to recognize clinically relevant patterns of brain function indicative of later emerging psychopathology. Once the proposed work is completed, we will have developed optimized protocols, and the first-ever opmMEG data collected in an infant, as well as the first ever simultaneous mother-infant opmMEG collected during naturalistic, physically-touching, social interactions. The innovations represented by this proposal are paramount to moving the field of infant imaging vertically to improve our understanding of neurodevelopment using salient social interactions that exist within the developmentally unique and formative mother-infant dyad.