Rewriting memories with red herrings

The researchers found a non-invasive way to selectively impair memories. http://www.flickr.com/photos/frisky21

Certain types of long term memories can be “rewritten” without drugs or surgery, according to a new study that experts say offers hope for sufferers of post traumatic stress disorder.

The study, conducted by Jason C. K. Chan and Jessica A. LaPaglia from Iowa State University, showed that declarative memories – memories of events, facts or details that can be consciously recalled – are open to change and can be disrupted through exposure to false details or alternative narratives.

The researchers designed an experiment in which participants were asked to watch an episode of the TV show 24 about a fictional terrorist attack.

Soon after the video ended, the participants were asked to recount the plot details. They were then asked to listen to an audio recording of a person explaining the video storyline, but with elements of misinformation woven throughout – for example, the suggestion that the villain used a stun gun on an airline attendant, when in the video it had been a hypodermic needle.

After being exposed to misinformation about plot details, the study subjects fared much worse at remembering the real details but only if the ‘re-learning’ occurred quite soon after the memory was first recalled.

“Here we show that existing declarative memories can be selectively impaired by using a noninvasive retrieval–relearning technique,” the authors said in their paper, which was published in the journal PNAS.

“These results demonstrate that human declarative memory can be selectively rewritten during reconsolidation.”

Post Traumatic Stress Disorder

Kristyn Bates, Research Assistant Professor of Experimental and Regenerative Neuroscience at the University of Western Australia said the new study was very interesting.

“The first thing that came to mind was that the data presented in this study could really help inform as to the best treatments for people who have conditions such as post-traumatic stress disorder, where unwanted memories can have such a devastating impact on a person’s life, through to better learning techniques for students studying for exams,” said Dr Bates, who was not involved in the study.

“Because declarative memory involves diffuse neuronal networks, it has been difficult to study in humans, unlike motor and fear-based memories which have localised, distinct neurological substrates. The authors have conducted a very well designed study where they have attempted to uncover whether declarative or long-term memories can be manipulated in humans without the use of drugs, which may have adverse side effects on other aspects of cognitive function.”

The authors of the study demonstrated that the incorrect details had to be specific, rather than vague, in order to be consolidated into the original memory, she said.

“This may explain why the numerous distractions and stimuli we encounter each day don’t destabilise our declarative memories. The memory-disruption effect was even present for items that participants had previously correctly recalled.”

Dr Bates said that further research was needed but the new findings may help to explain why certain forms of therapy are more effective for post traumatic stress disorder sufferers than others and may have important implications for crime investigation and interviewing of eye-witnesses.

“It is well known that eye-witness accounts can be manipulated. This study implies that the methods of questioning may be important for gathering reliable evidence. Importantly, this is a non-pharmacological, non-invasive technique, thus reducing the possibility of unwanted side effects on other memories and other aspects of cognition.”

Jee Hyun Kim, DECRA Fellow in Behavioural Neuroscience at The Florey Institute of Neuroscience and Mental Health, also welcomed the new findings.

“This study provides evidence how a stable ‘consolidated’ memory can be altered by what the person experiences following its recall,” said Dr Kim, who was not involved in the study.

“We already know that, especially in forensic context, existing memories can be manipulated and/or falsely remembered. This [study] explains how confabulation can be spontaneous as well as provoked. Confabulation is believed to depend on both subconscious and conscious processes. So far, reconsolidation studies provided subconscious ways in how a memory can be changed. [The new study] shows the conscious way.”

Dr Kim said that if brain imaging studies could be done while subjects recalled misinformed memories and original memories, “perhaps we can decode what confabulated memory looks like in the brain.”

“This could be used to differentiate true versus confabulated testimonies from eye witnesses in the court, or in diseases where confabulation is rampant such as Alzheimer’s, or alcoholism.”