Basically, you need a way of labeling neurons that were active during a specific experience, and a switch to operate them. (scientificamerican.com)
S to label neurons lining the digestive tract with a cocktail of three distinct fluorescent proteins. (sciencedaily.com)
Finally, hydroxystilbamadine, also known as fluoro - gold, is a dye that can be used as a retrograde enhancer for labelling neurons by injecting it in vivo. (abcam.com)