March 16, 2007

Researchers at New York University's LeDoux Laboratory have successfully deleted a single, targeted fear memory using drug therapy in rats. Their results, published in Nature Neuroscience, show that the removal of one memory from a rat's brain did not affect other memories there, and that the overall memory system was unharmed. The possibility of picking a particular memory to erase holds tremendous potential in treating people who suffer from post-traumatic stress disorder, anxiety disorders and other fear-related mental illnesses.

When the brain forms a memory, part of the process involves physically moving that memory from a neural network that supports short-term memory to one that holds long-term memories. The researchers, led by Joseph LeDoux, aimed to interrupt the transfer of a fear memory with the overall goal of deleting it. The way the scientists went about deleting the targeting memory implies that the act of recalling a memory involves a physical transfer as well. They were able to erase a memory by recalling it while the rats were under the influence of a drug call U0126, which induces limited memory loss (humans can't get it -- it's only approved for use in other animals).

The process they used for the study is fascinating. The researchers began with classical fear conditioning to create fear memories in a group of rats. They played two different musical tones, each one accompanied by an electric shock. The rats all developed two separate fears, one for each tone, which showed up in brain scans as increased neural activity in the amygdala, a part of the brain directly related to fear. Each time they heard either tone, they became afraid (presumably expecting the shock to follow).

Next, they divided the rats into two groups. The control group was left alone. The experimental group was drugged with U0126. All of the rats were then exposed to just one of the fear-inducing tones.

Once the experimental-group rats got the amnesia drug out their system, all of the rats were tested again. The researchers played both tones. The rats in the control group still showed increased activity in the amygdala in response to both tones. The rats in the experimental group only had a fear response to one of the tones. They were no longer afraid of the tone they'd been exposed to while under the influence of the drug. It's as if the process of recalling it brought it out of long-term memory, and the drug prevented it from being transferred back once the tone stopped playing.

Pointing to the change in amygdala activity, which is central to the brain's system of storing and recalling fearful memories (see How Fear Works to learn about this process), the researchers say the memory was not simply disconnected from fear, but that it was actually erased in its entirety. In other words, it was not that the rats learned not to be afraid of the tone; it was as if the rats had never learned to be afraid of the tone in the first place. And the fear of the second tone -- the one they'd not recalled while under U0126 -- was still active. The rest of the rats' memories appeared to be unaffected by the process.

The implications for the field of psychiatry are pretty staggering. Someone with a phobia of snakes or heights or flying could potentially receive treatment that would erase the phobia by bringing it up under the influence of a certain drug. People with post-traumatic stress disorder, whose lives are severely impacted a terrifying memory, could be cured by removing that memory from their brain.

And of course, the rest of us could use the process to wipe that person who broke our heart out of existence.

For more information on memory, fear and related topics, check out the following links:

Sources

  • "10 Questions for Joseph LeDoux." Gene Expression. Aug. 7, 2006. http://www.gnxp.com/blog/2006/08/10-questions-for-joseph-ledoux.php
  • "Emotion, Memory and the Brain." LeDoux Laboratory. NYU. http://www.cns.nyu.edu/home/ledoux/overview.htm
  • Jackson, Brian. "Drugs used to 'edit' fearful rat memories." DiscoveryReports. Mar. 13, 2007. http://reports.discoverychannel.ca/servlet/an/discovery/1/ 20070313/031307_discovery_memory_delete/ 20070313?hub=DiscoveryReport
  • "Scientists wipe out specific memory." The Times of India. Mar. 13, 2007. http://timesofindia.indiatimes.com/NEWS/Health__Science/ Scientists_wipe_out_specific_memory/articleshow/1759285.cms
  • Smith, Kerri. "Wipe out a single memory." Nature.com. Mar. 11, 2007. http://www.nature.com/news/2007/070305/full/070305-17.html