Optogenetics is an emerging neuroscience technique in which light-activated transmembrane ion channels are introduced to achieve optical control of defined action potential patterns in specifically targeted neuron populations. Since optogenetics allows temporally precise modulation over neuronal activity in vivo, by combining optogenetic control and fMRI, neural activity arising from specific circuit elements and its signaling impact on the rest of circuit can be monitored across the whole brain. In our lab, we combine optogenetics and fMRI in awake animals to determine how specific cell types and their signaling impact fMRI signal.