The findings, published Jan. The experiment showed that people are capable of repeatedly blocking thoughts of experiences they don't want to remember until they can no longer retrieve the memory, even if they want to, Gabrieli explained.
Michael Anderson, a psychology associate professor at the University of Oregon and the paper's lead author, conducted the experiment with Gabrieli and other researchers during a sabbatical at Stanford last year. The study provides a clear model for how this occurs by grounding it firmly in an essential human ability -- the ability to control behavior. In recent years, the question of repressed memory has attracted considerable public attention concerning cases involving childhood sexual abuse.
Anderson first revealed the existence of such a suppression mechanism in the brain in a paper published in Nature titled "Suppressing Unwanted Memories by Executive Control. The core findings showed that controlling unwanted memories was associated with increased activation of the left and right frontal cortex the part of the brain used to repress memory , which in turn led to reduced activation of the hippocampus the part of the brain used to remember experiences.
In addition, the researchers found that the more subjects activated their frontal cortex during the experiment, the better they were at suppressing unwanted memories.
Twenty-four people, aged 19 to 31, volunteered for the experiment. Participants were given 36 pairs of unrelated nouns, such as "ordeal-roach," "steam-train" and "jaw-gum," and asked to remember them at 5-second intervals.
The subjects were tested on memorizing the word pairs until they got about three-quarters of them right -- a process that took one or two tries, Anderson said. Now, in a new paper in Current Biology , Ramirez and a team of collaborators have shown just how pliable memory is if you know which regions of the hippocampus to stimulate -- which could someday enable personalized treatment for people haunted by particularly troubling memories.
In their study, Chen and Ramirez, the paper's senior author, show how traumatic memories -- such as those at the root of disorders like PTSD -- can become so emotionally loaded. By artificially activating memory cells in the bottom part of the brain's hippocampus, negative memories can become even more debilitating. In contrast, stimulating memory cells in the top part of the hippocampus can strip bad memories of their emotional oomph, making them less traumatic to remember.
Using a technique called optogenetics, Chen and Ramirez mapped out which cells in the hippocampus were being activated when male mice made new memories of positive, neutral, and negative experiences.
A positive experience, for example, could be exposure to a female mouse. In contrast, a negative experience could be receiving a startling but mild electrical zap to the feet.
Then, identifying which cells were part of the memory-making process which they did with the help of a glowing green protein designed to literally light up when cells are activated , they were able to artificially trigger those specific memories again later, using laser light to activate the memory cells. Their studies reveal just how different the roles of the top and bottom parts of the hippocampus are. Activating the top of the hippocampus seems to function like effective exposure therapy, deadening the trauma of reliving bad memories.
But activating the bottom part of the hippocampus can impart lasting fear and anxiety-related behavioral changes, hinting that this part of the brain could be overactive when memories become so emotionally charged that they are debilitating. That distinction, Ramirez says, is critical. He says that it suggests suppressing overactivity in the bottom part of the hippocampus could potentially be used to treat PTSD and anxiety disorders. It could also be the key to enhancing cognitive skills, "like Limitless," he says, referencing the film starring Bradley Cooper in which the main character takes special pills that drastically improve his memory and brain function.
Memories are usually stored in networks that make them easily accessible to consciously remember. The findings suggest that when faced with traumatic stress, the brain can activate a different system to form and suppress memories.
Moreover, the study shows that there are multiple pathways of storing memories. While the Northwestern Medicine scientists only identified the first of these pathways, this research could some day lead to new treatments for patients for whom conscious access to memories is integral to recovery. Learn the difference between a stroke and an aneurysm. Prevention and treatment through the decades. Study Reaches Repressed Memories for New Mental Health Therapies Scientists believe suppressed memories are created by a process called state-dependent learning.
What is a Hidden Memory? Multiple Pathways Hide Memories Chemical receptors in the brain control emotional tides, excitement and calm. New Insight for Mental Health Therapies The scientists believe that this different system may be a protective mechanism in the brain for when an experience is overwhelmingly stressful. You Might Also Like. Medical Advances.
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