How whole groups of neurons work together to form Pavlovian classical conditioning of two stimuli was recently investigated by Professor Mark Schnitzer's lab. The researchers worked with mice and focused on the amygdala, a part of the brain known to be involved in learning that is extremely similar across species. They taught mice to associate a tone with a mild shock and found 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. Using Pavlov’s dogs as an analogy, this would mean that, as the dogs learned to associate the bell with the food, the neural network activation in their amygdalas would look similar whether they were presented with food or just heard the bell.
The researchers’ results, published in Nature on March 22, also reveal that the neurons never returned to their original state, even after the training was undone. Although this was not the main focus of the study, this research could have wide-ranging implications for studying emotional memory disorders, such as post-traumatic stress disorder (PTSD).