Yahiro, T.; Chen, Y.; Bayless-Edwards, L.; An, S.; Mao, T.; Zhong, H.

Fluorescence lifetime measurements overcome the limitation of widely used intensity-based measurements in quantifying tonic activities and longitudinal changes in neural dynamics. However, while lifetime sensors are rapidly emerging, their applications have been limited by the complexity and expense of required hardware and software. Here, we report a simple, low-cost lifetime fiber photometry system, named iFLiP, that uses entirely off-the-shelf products and can be assembled without specialized expertise. We also develop software that enables turn-key operation. The integrated system can accurately monitor lifetime changes at up to 5000 Hz for days. We demonstrate the utility of iFLiP in monitoring the activity of protein kinase A (PKA) in vitro and in vivo, and uncover striatal subregion- and cell-type-specific PKA dynamics elicited by locomotion in mice. Additionally, multi-day continuous measurements in the basal forebrain reveal previously unappreciated PKA activity associated with sleep/wakefulness. Overall, iFLiP may make lifetime measurements broadly accessible in neuroscience research.