<p><span>The capacity to remember temporal relationships between different events is essential to episodic memory, but little is currently known about its underlying mechanisms. We performed time-lapse imaging of thousands of neurons over weeks in the hippocampal CA1 of mice as they repeatedly visited two distinct environments. Longitudinal analysis exposed ongoing environment-independent evolution of episodic representations, despite stable place field locations and constant remapping between the two environments.

<p><span>Recording neuronal activity in behaving subjects has been instrumental in studying how information is represented and processed by the brain. Recent advances in optical imaging and bioengineering have converged to enable time-lapse, cell-type specific recordings of neuronal activities from large neuronal populations in deep-brain structures of freely behaving rodents. We will highlight these advancements, with an emphasis on miniaturized integrated microscopy for large-scale imaging in freely behaving mice.