Though Hollywood has warned us that selectively erasing bad memories might have disastrous consequences, the prospect of forgetting traumatic experiences remains intriguing. A new study in mice suggests that this type of memory deletion might one day be possible, as researchers have managed to target the neurons involved in a single memory and to zap them—and the memory—into oblivion.

Scientists have long suspected that each memory can be traced to a particular group of neurons, but it has been difficult to isolate such neurons because they are scattered in different areas of the brain. In a previous study, however, Sheena Josselyn (Hospital for Sick Children and University of Toronto, Canada) and colleagues identified specific neurons that were involved in fear-related memories. When a mouse was trained to create a fear memory, neurons in the lateral amygdala with high expression of the protein CREB (cyclic adenosine monophosphate response element–binding protein) were more likely to be activated compared with other neurons.

In their new study, Josselyn and colleagues injected mice with a vector that caused some of their neurons to overexpress CREB and to become vulnerable to a specific toxin (Science 323, 1492–1496; 2009). Three days after injection, the researchers placed each mouse in a conditioning chamber and exposed it to a tone followed by a shock to the foot. This caused the mouse to create an auditory fear memory: ordinarily, a mouse exposed to the same tone a day later would immediately 'freeze' in anticipation of the shock. After the training session, the researchers injected the mouse with the toxin that killed neurons overexpressing CREB—neurons that would presumably have been recruited to create the new fear memory. When mice were exposed to the tone the following day, they showed no signs of fear, indicating that their fear memories had been deleted along with the neurons.

The fear memories seemed to have been erased completely and did not resurface over time. Killing the neurons did not seem to impair subjects' ability to acquire new fear memories; mice could be retrained to fear the shock. Furthermore, memories that were created before the injection of the vector were not affected.

The study sheds light on how memories are stored in the brain and shows that memory-specific neurons can be traced and manipulated. The ability to selectively eliminate fear memories might also have therapeutic applications, such as treatment of post-traumatic stress disorder.