Techniques used in the lab in freely behaving mice Optogenenetics and electrophysiology to manipulate circuits during defined behavioural states. Calcium imaging with miniscopes to follow neuronal assemblies during learning and recall. Calcium imaging coupled with either electrophysiology and/or optogenetics. Neuroanatomical techniques using viral tracing techniques. Lab Tools Engineering In vivo calcium imaging is a technique being adopted in the Williams laboratory and is quickly becoming central to the work of essentially all experimenters. It consists of capturing digital fluorescence microscopy through a special fenestration in the skull of a mouse. Through genetic engineering the mouse’s neurons express proteins whose fluorescence depends on calcium binding. Calcium concentration in nerve cells is integral to their function and the fluorescence indicating dynamic calcium concentration can be obtained concurrent to behavior using a miniature camera worn by the mouse. Manufacturing of the calcium imaging cameras, a variation of the UCLA Miniscope, is done in-house using off-the-shelf and custom-made components, including Delrin and Ultem parts machined on a 5-axis CNC milling machine.