Abstract: Hemodynamic signals allow us to non-invasively assay neural activity and could provide great insight into neural changes during postnatal development. However, it is not clearly understood how neural activity is related to changes in blood flow and oxygenation in the neonatal and juvenile brain. Previous studies in anesthetized animals and sedated humans have come to conflicting results as to the sign and magnitude of neurovascular coupling, and this unresolved issue has stalled the use of hemodynamic imaging in infants and children. In this proposal, we will determine how neurovascular coupling changes during postnatal development in the somatosensory cortex of the awake mouse brain, how this change in neurovascular coupling impacts BOLD fMRI signals, and how behavioral state can alter neurovascular coupling. We will use a multimodal approach, combining optical imaging (intrinsic optical signal imaging and 2-photon microscopy), electrophysiology, and fMRI to elucidate the relationship of hemodynamic signals to neural activity from the levels of single vessels up to the whole brain. We will mechanistically dissect the roles of local neural activity and cardiovascular effects on hemodynamic signals. The research proposed here will enable the use of hemodynamic imaging to study neural activity, plasticity, and neurodevelopmental disorders in infants and juvenile humans and animals.