Stanford University researchers teach mice to associate a tone with a mild shock and find that, once the mice learned the association, the pattern of neurons that activated in response to tone alone resembled the pattern that activated in response to the shock. Analogous to Pavlov’s dogs, the researchers then expected the neural network activation in the mice amygdalas would look similar whether they were presented with a shock or just heard the tone. At the beginning of the experiment, the mice had no reaction to the tone, but would freeze in place in response to the light shock. After pairing the tone and the light shock a few times, the tone alone was enough to cause the mice to freeze in place. Researchers viewed neurons deep in the brain and found that, as the mice learned to associate the tone with the shock, the set of cells that responded to the tone began to resemble those that responded to the shock itself. The amount of change in how the group of neurons responded to the tone also predicted how much the mouse behavior would change. As part of the experiments, the team also undid the conditioning so that the mice stopped freezing in reaction to the tone. During this phase, however, the neural response never completely returned to its original state.