Researchers from the University of California and San Diego School of Medicine have achieved a remarkable feat by erasing and then reactivating memories in rats. Researchers profoundly altered rodents’ reaction to past events by weakening and strengthening the connections between nerve cells called synapses. They stimulated neurons in the brains of the rats with a series of light pulses that have been previously shown to strengthen or weaken the connections between brain cells.
In the course of the research, scientists optically stimulated a group of nerves in the rat’s brain (which equated to the sound of a tone) that were genetically modified to be sensitive to light. Simultaneously, a mild shock was delivered to the animal’s foot, which caused the rat to associate the optical nerve stimulation with pain of a mild shock. Later, whenever the same nerves were stimulated, the rats displayed fear. Analysis showed that chemical changes within the optically stimulated nerve synapses led to strengthening of the synapse, creating a memory. In the next stage, researchers weakened the connection in the synapses by stimulating the same nerves with a memory-erasing, low frequency train of optical pulses. The same rats did not respond to the original fear of nerve stimulation, suggesting an erasure of the pain-associated memory.
However, the highlight of the research is the fact that scientists reactivated the lost memory by re-stimulating the same nerves with a memory-forming high-frequency train of optical pulses. The rats responded with fear to the stimulation without any electric shock. The research can be helpful in treating Alzheimer’s or PTSD wherein the synaptic connections weaken because of beta amyloid peptide accumulation in the brains of the patients.