Got a bad memory you’d like to get rid of?
A pair of UC Riverside researchers say they have developed a technique that might make that possible.
Right now, you have to be a mouse to benefit from the process. But Jun-Hyeong Cho, a professor of cell biology and neuroscience and postdoctoral researcher Woong Bin Kim hope the work they are doing can one day be used on humans, particularly those who may suffer from post-traumatic stress disorder or crippling phobias.
Their work is one of a string of recent studies in which different techniques have been used to erase brain memory. Cho and Kim’s experiment is different in that they used light to trigger the process.
In a paper in the current issue of Neuron magazine, the two outline a study in which lab mice were trained to recognize two sounds, one a high-frequency sound, the other a low-frequency sound. The high-frequency sound was paired with a mild electrical shock, so that the mice learned to fear the tone, even when no shock was given.
Prior to the training, the brains of the mice were genetically altered in a way that made their high-frequency auditory neurons react to stimulation by blue light. A thin tube with a 2 mm fiber optic emitter was surgically implanted near those neurons. When that light was turned on, the neurons would fire.
When a memory is formed, new connections between neurons are formed. This takes place at the synapse, the space between the neurons where neurotransmitters flow from one cell to another. The neurons receiving the neurotransmitters form receptors for those chemicals. The stronger the memory, the more receptors are formed.
In the case of the fear memory in the mice, Cho and Kim were looking at the neural pathway between the auditory center and the amygdala, the part of the brain that processes fear responses.
They repeatedly stimulated the neurons that triggered the fear of high-pitched sound, but did so with a low frequency of stimulation. Lower stimulation, Cho said, actually weakens a memory. Fewer neurotransmitters are released and receptors specific to the memory begin to disappear. After a period of time, the mice no longer showed fear when the high-pitch neurons were stimulated. The memory was gone.
Scientifically erasing memory may remind some people of the 2004 film “Eternal Sunshine of the Spotless Mind,” in which characters played by Jim Carrey and Kate Winslet elect to erase the memories of their relationship and painful breakup. Cho said he is familiar with the movie.
“Five to 10 years ago, the manipulation of memory was science fiction,” he said. “But now it’s not.”
While he says science is just knowledge, he did admit that he has concerns about how the techniques being developed might eventually be used.
“There are a lot of ethical issues,” he said. “We all consider whether this would be eventually beneficial to the society. We don’t want a situation such as ‘Total Recall,’” the 1990 Arnold Schwarzenegger sci-fi thriller that revolves around implanted memories.
He also realizes that not all negative memories are bad.
“If we have a bad memory and it makes us avoid that thing in the future, that’s a good thing,” he said. “That’s adaptive learning.”
Debilitating, or pathological, memories, however, are not helpful, he said. He sees many potential benefits in being able to erase memory, such as possible treatments for mental illness, Alzheimer’s disease and PTSD.
The current standard treatment for PTSD is desensitization through repeated recall of the memory — in a way similar to the low-level stimulation given to the mice in the UCR study. But Cho said research has shown that the weakened memories rebound after treatment.
“Normally, two to three weeks after (therapy) it relapses,” Cho said. “That’s why we think experiential therapy is very frustrating” for some patients.
With the technique he and Kim used, they didn’t see that problem.
“In our case, we did not observe a relapse of fear,” he said.
Psychological conditions such as depression and bipolar disorder have been treated as problems with the chemical balance in the brain in recent years. Cho said about 30 percent of patients don’t respond to drugs such as Prozac. He thinks physical mechanisms may be involved.
“It could be a neural circuitry problem,” he said. If the specific neurons can be identified, he added, “We can artificially manipulate the strength of that connection to (potentially) relieve the symptoms.”
Reversing the procedure, where added stimulation of neurons could help strengthen memories, might benefit patients with Alzheimer’s or dementia, he said.
Having shown he can erase memory, Cho said he wants to explore going in the other direction.
“I want to try to implant new memories,” he said.