'Bad memories' can be selectively erased: study

Memories that trigger anxiety and post-traumatic stress disorder (PTSD) could be erased without affecting other important memories of past events, according to a study.
The finding could help develop drugs that can treat anxiety without affecting the patient's normal memory, researchers said.
Brains create long-term memories by increasing the strength of connections between neurons and maintaining those connections over time.
The study, published in the journal Current Biology, tested that hypothesis by stimulating two sensory neurons connected to a single motor neuron of the marine snail Aplysia.
One sensory neuron was stimulated to induce an associative memory and the other to induce a non-associative memory.

"The example I like to give is, if you are walking in a high-crime area and you take a shortcut through a dark alley and get mugged, and then you happen to see a mailbox nearby, you might get really nervous when you want to mail something later on," said Samuel Schacher, professor of neuroscience at Columbia University Medical Centre (CUMC).

In the example, fear of dark alleys is an associative memory that provides important information based on a previous experience.
Fear of mailboxes, however, is an incidental, non-associative memory that is not directly related to the traumatic event.
By measuring the strength of each connection, the researchers found that the increase in the strength of each connection produced by the different stimuli was maintained by a different form of a Protein Kinase M (PKM) molecule (PKM Apl III for associative synaptic memory and PKM Apl I for non- associative).

They found that each memory could be erased - without affecting the other - by blocking one of the PKM molecules.
They found that specific synaptic memories may also be erased by blocking the function of distinct variants of other molecules that either help produce PKMs or protect them from breaking down.
"By isolating the exact molecules that maintain non- associative memory, we may be able to develop drugs that can treat anxiety without affecting the patient's normal memory of past events," said Jiangyuan Hu, an associate research scientist in the Department of Psychiatry at CUMC.