Posts tagged memory reconsolidation
Articles and news from the latest research reports.
Xenon Exposure Shown to Erase Traumatic Memories
McLean Hospital researchers are reporting that xenon gas, used in humans for anesthesia and diagnostic imaging, has the potential to be a treatment for post-traumatic stress disorder (PTSD) and other memory-related disorders.
“In our study, we found that xenon gas has the capability of reducing memories of traumatic events,” said Edward G. Meloni, PhD, assistant psychologist at McLean Hospital and an assistant professor of Psychiatry at Harvard Medical School. “It’s an exciting breakthrough, as this has the potential to be a new treatment for individuals suffering from PTSD.”
In the study, published in the current issue of PLOS ONE, Meloni, and Marc J. Kaufman, PhD, director of the McLean Hospital Translational Imaging Laboratory, examined whether a low concentration of xenon gas could interfere with a process called reconsolidation – a state in which reactivated memories become susceptible to modification. “We know from previous research that each time an emotional memory is recalled, the brain actually restores it as if it were a new memory. With this knowledge, we decided to see whether we could alter the process by introducing xenon gas immediately after a fear memory was reactivated,” explained Meloni.
The investigators used an animal model of PTSD called fear-conditioning to train rats to be afraid of environmental cues that were paired with brief footshocks. Reactivating the fearful memory was done by exposing the rats to those same cues and measuring their freezing response as a readout of fear. “We found that a single exposure to the gas, which is known to block NMDA receptors involved in memory formation in the brain, dramatically and persistently reduced fear responses for up to 2 weeks. It was as though the animals no longer remembered to be afraid of those cues”, said Dr. Meloni.
Meloni points out that the inherent properties of a gas such as xenon make it especially attractive for targeting dynamic processes such as memory reconsolidation. “Unlike other drugs or medications that may also block NMDA receptors involved in memory, xenon gets in and out of the brain very quickly. This suggests that xenon could be given at the exact time the memory is reactivated, and for a limited amount of time, which may be key features for any potential therapy used in humans.”
“The fact that we were able to inhibit remembering of a traumatic memory with xenon is very promising because it is currently used in humans for other purposes, and thus it could be repurposed to treat PTSD,” added Kaufman.
For these investigators, several questions remain to be addressed with further testing. “From here we want to explore whether lower xenon doses or shorter exposure times would also block memory reconsolidation and the expression of fear. We’d also like to know if xenon is as effective at reducing traumatic memories from past events, so-called remote memories, versus the newly formed ones we tested in our study”.
Meloni and Kaufman indicate that future studies are planned to test if the effects of xenon in rats seen in their study translate to humans. Given that intrusive re-experiencing of traumatic memories – including flashbacks, nightmares, and distress and physiological reactions induced when confronted with trauma reminders – is a hallmark symptom for many who suffer from PTSD, a treatment that alleviates the impact of those painful memories could provide welcome relief.
(Source: mcleanhospital.org)
Treating Mental Illness by Changing Memories of Things Past
In the novel À larecherche du temps perdu (translated into English as Remembrance of Things Past), Marcel Proust makes a compelling case that our identities and decisions are shaped in profound and ongoing ways by our memories.
This truth is powerfully reflected in mental illnesses,like post traumatic stress disorder (PTSD) and addictions. In PTSD, memories of traumas intrude vividly upon consciousness, causing distress, driving people to avoid reminders of their traumas, and increasing risk for addiction and suicide. In addiction, memories of drug use influence reactions to drug-related cues and motivate compulsive drug use.
What if one could change these dysfunctional memories? Although we all like to believe that our memories are reliable and permanent, it turns out that memories may indeed be plastic.
The process for modifying memories, depicted in the graphic, is called memory reconsolidation. After memories are formed and stored, subsequent retrieval may make them unstable. In other words, when a memory is activated, it also becomes open to revision and reconsolidation in a new form.
"Memory reconsolidation is probably among the most exciting phenomena in cognitive neuroscience today. It assumes that memories may be modified once they are retrieved which may give us the great opportunity to change seemingly robust, unwanted memories," explains Dr. Lars Schwabe of Ruhr-University Bochum in Germany. He and his colleagues have authored a review paper on the topic, published in the current issue of Biological Psychiatry.
The idea of memory reconsolidation was initially discovered and demonstrated in rodents.
The first evidence of reconsolidation in humans was reported in a study in 2003, and the findings have since continued to accumulate. The current report summarizes the most recent findings on memory reconsolidation in humans and poses additional questions that must be answered by future studies.
"Reconsolidation appears to be a fundamental process underlying cognitive and behavioral therapies. Identifying its roles and mechanisms is an important step forward to fully harnessing the reconsolidation process in psychotherapy," said Dr. John Krystal, Editor of Biological Psychiatry.
The translation of the animal data to humans is a vital step for the potential application of memory reconsolidation in the context of mental disorders. Memory reconsolidation could open the door to novel treatment approaches for disorders such as PTSD or drug addiction.
Discovery of new means to erase pain
A study published in the scientific journal Nature Neuroscience by Yves De Koninck and Robert Bonin, two researchers at Université Laval, reveals that it is possible to relieve pain hypersensitivity using a new method that involves rekindling pain so that it can subsequently be erased. This discovery could lead to novel means to alleviate chronic pain.
The researchers from the Faculty of Medicine at Université Laval and Institut universitaire en santé mentale de Québec (IUSMQ) were inspired by previous work on memory conducted some fifteen years ago. These studies had revealed that when a memory is reactivated during recall, its neurochemical encoding is temporarily unlocked. Simultaneous administration of a drug that blocks neurochemical reconsolidation of the memory results in its erasure.
The investigators wanted to see whether a similar mechanism was at play during neurochemical encoding of pain sensitization. To this end, they injected capsaicin in the foot of mice. Capsaicin, the pungent chemical in chili pepper, triggers a burning sensation. The procedure, which causes no physical damage, triggers pain hypersensitivity through a process of protein synthesis in the spinal cord. After capsaicin injections, the mechanical pressure at which mice would flinch was about a third of that in the normal situation.
Three hours later, the researchers administered a second dose of capsaicin and, at the same time, a drug that blocks protein synthesis. The hypersensitivity then vanished rapidly. Within less than 2 hours, the pressure tolerated by the mice was back to 70% of normal.
Yves De Koninck explains that “when the protein synthesis inhibitor is administered alone, the hypersensitivity remains. The second injection of capsaicin is necessary to render the sensitivity to pain unstable and be able to interfere with its neurochemical reconsolidation. The challenge now will be to find protein synthesis inhibitors that are nontoxic and cause minimal side effects in humans”.