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A study by UCLA psychologists provides strong evidence that a certain region of the brain plays a vital role in recalling memory. The research, published in the Journal of Cognitive Neuroscience, also shows for the first time that the use of an electric current to stimulate this region, the left rostrolateral prefrontal cortex, improves the ability of people to recover memories.
"We have seen a dramatic improvement in memory performance by increasing the excitability of this region," said Jesse Rissman, badistant professor of psychology at UCLA, as well as the lead author of the study, a specialist in psychiatry and behavioral sciences.
The left rostrolateral prefrontal cortex is important for high-level thinking, including monitoring and integrating information processed in other brain regions, Rissman said. This area is located behind the left side of the forehead, between the eyebrow and the hairline.
"We think this area of the brain is particularly important for accessing and making decisions about the knowledge you have formed in the past," said Rissman, also a member of the Brain Research Institute, UCLA.
Psychologists conducted experiments on three groups of people whose average age was 20 years old. Each group included 13 women and 11 men.
Participants viewed a series of 80 words on a computer screen. For each word, participants were asked to imagine either themselves or another person interacting with the word, depending on whether the words "self" or "other" also appear on the screen. (For example, the combination of "gold" and "other" might make them imagine a friend with a gold necklace.)
The next day, the participants returned to the laboratory for three tests: one of their memory, one of their reasoning ability and one of their visual perception. Each participant wore a device that sent a weak electrical current through an electrode on the scalp to decrease or increase the excitability of the neurons in the left rostrolateral prefrontal cortex. By increasing their excitability, neurons are more likely to trigger, which improves the connections between neurons, said Rissman.
(The technique, called transcranial direct current stimulation, or tDCS) gives most people a warm, gentle tingling sensation for the first few minutes, said lead author Andrew Westphal. who conducted the study as a PhD student at UCLA. Postdoctoral Fellow in Neurology at the University of San Francisco.)
During the first half of the study, all participants received "dummy" stimulation, which means that the device was turned on briefly to make the sensation that something was happening, then was turned off so that No electrical stimulation is applied. This allowed researchers to measure how well each participant performed the tasks under normal conditions. Over the next 30 minutes, a group of participants received an electrical current increasing the excitability of their neurons, the second group received a current that inhibited neuron activity, and the third group received only dummy stimulation. . The researchers badyzed which group best remembered the words seen the day before.
First, the scientists noted that there was no difference between the three groups during the first half of the study – in the absence of brain stimulation – any difference in the second half of the experiment could be attributed to stimulation, said Westphal.
The memory scores of the group whose neurons received excitatory stimulation in the second half of the study were 15.4 points higher than their scores when they received dummy stimulation.
Scores for those who received false stimulation in both sessions increased by only 2.6 percentage points between the first and second sessions – a statistically insignificant change that was likely due to their increased familiarity with the task , according to the document. And the scores for the group whose activity of neurons was temporarily suppressed increased by only five percentage points, which the authors also wrote was not statistically significant.
"Our previous neuroimaging studies have shown that the left rostrolateral prefrontal cortex is heavily engaged in memory recovery," said Rissman. "Now, the fact that people perform better this task of memory when we excite this region with electrical stimulation provides a causal proof that it contributes to the act of memory recovery.
"We did not think that the application of low electrical stimulation of the brain would make their memories perfect, but the fact that their performance has increased as much as it has been surprising and it is an encouraging sign that this method could potentially be used to improve people's memory. . "
The reasoning task of the study asked participants to decide in seven seconds whether certain word pairs were badogies. Half of the essays had word pairs that were true badogies, such as "moat" means "castle", while "firewall" means "computer". (In both pairs, the first word protects the second against the invasion.) The other half had pairs of words that were related but that were not badogous.
The researchers found no significant difference in performance between the three groups.
For the final, perception-based task, subjects were asked to choose which of the four words had the most straight lines in their printed form. (An example: among the words "symbol", "museum", "painter" and "energy", the word "museum" has the straightest lines.) Again, the researchers found no significant difference between the three groups – what Rissman said was planned.
"We were expecting to find an improvement in memory, and we did," said Rissman. "We also predicted that the reasoning task could improve with increased excitability, but this is not the case. We did not think that this region of the brain would be important for the task of perception. "
Why do people forget names and other words? Sometimes it's because they do not pay attention when they hear it or see it for the first time, so that no memory is even formed. In these cases, electrical stimulation would not help. But in cases where a memory is formed but is difficult to recover, stimulation can help to access it.
"Stimulation helps people access memories that they would otherwise have reported as forgotten," said Westphal.
Although TDCS devices are commercially available, Rissman does not recommend anyone to try them out of supervised research.
"Science is still in its infancy," he said. "If you do this at home, you could stimulate your brain insecurely, with too much current or too long."
Rissman said that other areas of the brain also play an important role in recovering memories. Their future research will aim to better understand the contributions of each region, as well as the effects of brain stimulation on other types of memory tasks.
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