The Science of Eternal Sunshine: Scientists Erase and Restore Memories in Rats
If you could remove a painful memory, Eternal Sunshine-style, would you? If your answer is yes, then you're in luck. A team of neuroscientists at UCSD has manipulated neural connections in rats to both erase and restore a memory.
The scientists used classical conditioning in order to train the rats to associate light with pain. Previously, these kinds of experiments were conducted using auditory stimulation, such as tones, but these experiments did not have the precision needed to prove a causal relationship between the memory and the neural stimulation. As an alternative, they used optogenetic stimulation, or stimulating a group of nerves in the rats' brains that had been genetically modified to make them sensitive to light. Simultaneously, they delivered an electric shock to the animal's foot. The rats became afraid of the light, as they associated it with the electric shock. After this step, they observed that the neural connections that had been stimulated during this part of the experiment were strengthened.
The team then varied the pattern of the optogenetic stimulation in a process known to weaken these connections. After a low-frequency sequence of optical pulses, the team had effectively erased the memory in the rats and they no longer had a fear response to the stimulation.
In order to then recover the fear memory, they once again strengthened the neural connections that caused the fear responses by stimulating the rats with a sequence of high-frequency optical pulses. The rats once again responded to the original stimulation with fear, even though no electric shock had been applied. This provides evidence for the theory that scientists have long been propagating, but for which they have never had concrete evidence: that memories are formed by a process called long-term potentiation, or the strengthening of connections between neurons.
In response to these findings, lead author Robert Manilow says, "We can form a memory, and then turn it off and turn it on by selectively turning on synapses."
Although this technology is still in its infancy, these findings could be the first step to memory manipulation in humans, perhaps as some sort of treatment for PTSD or Alzheimer's.
"We have shown that the damaging products that build up in the brains of Alzheimer's disease patients can weaken synapses in the same way that we weakened synapses to remove a memory," Malinow said. "So this line of research could suggest ways to intervene in the process."