"We’d like to understand how a rat makes a decision. A decision, in this case, involves a sensory cue, an odor, and a meaning for that odor that the rat has learned because we’ve trained it in a particular way.

"The decision happens somewhere in the brain, where sensory information comes together with memory, with learning, and with motivation. In this case, the rat is motivated to find water. So it's learned a particular cue.

"The rat has a very keen sense of smell. Rats can discriminate between any pair of chemicals. There are actually many things that you or I couldn’t distinguish that a rat has no problem learning to tell apart.

"They use odors in their social lives, as sources of food or to avoid predators, and to navigate. They’re very attuned to smell versus vision or hearing. We take advantage of that in our experiments by using odors to direct their behavior."Essentially, we will teach the rat that this particular odor means it will get water as a reward. An odor can serve as a cue for the rat to tell it where to go and at what time.

"These electrodes are very thin wires. It’s relatively noninvasive. The rat will recover from the surgery and go back into this behavioral chamber. We’ll record, for example, from the neurons in the part of the brain that receives olfactory information, the olfactory bulb, or parts of the brain that are further along the line toward the execution of a movement, for example.

"There’s a compromise between what you can do ethically in an organism, and the organism being close to humans. You cannot ask someone to open up their head and examine it with electrophysiological tools that do certain kinds of invasive imaging when it’s possible to do it in a simpler organism. So we get a level of analysis that is only possible in humans very rarely, such as the case of a patient having surgery for epilepsy, for example. In humans, we get a much coarser view of the brain."

—Zach Mainen, neuroscientist at Cold Spring Harbor Laboratory