There is so much about memory and how our brains make them that we don't know, but thanks to new research, scientists are now one step closer to understanding how certain sensations, such as sounds, trigger certain memories.

In a new study, scientists mapped nerve cells in the brains of rats as they learned to make certain choices as a response to certain sounds. This map proved so accurate that scientists could then predict what choices a rat would make when it heard a certain sound.

This is important because it helps us understand how the human brain uses such sensations in forming memories.

"For decades scientists have been trying to map memories in the brain," says James Gnadt, Ph.D., program director at the National Institute of Neurological Disorders and Stroke. "This study shows that scientists can begin to pinpoint the precise synapses where certain memories form and learning occurs."

The synapses responsible for recording these memories in mice happened in the striatum part of the brain, which is thought important for connecting sensation into thoughts and actions. This is also the part of the brain that malfunctions with diseases that affect skill learning in humans, such as Huntington's disease.

Scientists began by studying the electrical responses in the rats' brains, particularly in the striatum. This allowed them to map out the brain and how it responded to sensations, as well as translating thoughts into action. They also injected light-sensitive molecules into the part of the brain responsible for translating the hearing of sound into thought.

Scientists trained rats with auditory tones, some with high pitches, some with low pitches. They accompanied the pitches with the opening of one of three doors that contained food for the rodents. The rats quickly learned how to associate specific tones with specific doors.

After studying the rats' brains, the team mapped which part of the rats' brains responded to specific tones and translated those tones into thoughts, which resulted in action, thereby mapping out the process of the rats remembering which tones they associated with which actions.

"We literally watched the synapses listen and learn to respond to very specific sounds over the course of the training," says Anthony Zador, M.D., Ph.D., professor at Cold Spring Harbor Laboratory, New York. "This study is a great example of how the brain can turn senses -- sights, sounds, smells -- into meaning."