Neuronal circuits develop, adjust to experience and degenerate in response to injury or disease in the course
of weeks and months. Available recording techniques, however, typically sample physiological properties of
identified neurons on the time scale of minutes and hours. Thus, in order to obtain a full understanding of a
long term physiological process data need to be extrapolated from numerous experimental sessions and animals,
often collected blindly and under variable conditions. The generation and ongoing engineering of genetically
encoded calcium indicators creates an opportunity to repeatedly record activity from the same
individual neurons in vivo over weeks, months and potentially the entire lifetime of a model organism.
Chronic calcium imaging with genetically encoded indicators thus may allow to establish functional biographies
of identified neuronal cell types in the brain and to reveal the physiological relevance of structural
changes as they occur under natural and pathological conditions.