Fiber photometry is a technique that's highly effective for recording bulk or population-level neuronal activity. In the lab, it's used to monitor calcium activity, serving as a proxy for neuronal firing, and for neurotransmitter activity. These reporters are genetically encoded proteins that fluoresce upon binding with neurotransmitters, making it possible to track neurotransmitter activity. The lab currently utilizes this technique for both dopamine and GABA monitoring. This method involves implanting an optical fiber into the brain, which allows for the delivery of excitation light and the measurement of resultant fluorescence from the targeted neuronal population. This approach is particularly useful for long-term studies and for analyzing event-related data, such as calcium signals aligned with specific behavioral events. Fiber photometry has become invaluable in neuroscience for its ability to provide insights into neural circuit dynamics and neurotransmitter activity in vivo.