How do you make a memory? One important ingredient researchers have been studying is calcium. Daniel Johnston, a professor of neuroscience at Baylor College of Medicine (Houston, TX), and his colleagues use charge-coupled-device (CCD) cameras capable of detecting very low levels of light to watch the mechanisms they think trigger memories and learning. It's a demanding application, and scientists are counting on improvements in imaging technology to help them see more.
The researchers start with slices of a rat's brain and stimulate them electrically to mimic neural activity that goes on during learning. They treat the brain with a fluorescent dye and illuminate it with 380-nm light from a tungsten bulb. The dye emits around 500 nm when it binds to a calcium ion. The CCD camera allows them to record changes in calcium concentration throughout a neuron, including both the central cell body and the branching dendrites—the jagged twigs that transmit information to neighboring neurons.