It may sound like something out of Eternal Sunshine of the Spotless Mind. But scientists have discovered that different types of memories stored in the same neuron can be selectively erased, according to a new study by researchers at Columbia University Medical Center (CUMC) and McGill University.
The study in the journal Current Biology, suggest that scientists may be able to develop drugs which delete select memories that trigger anxiety and post-traumatic stress disorder (PTSD) without affecting other important memories of past events.
According to researchers, multiple memories can become encoded during emotional or traumatic events, such as memories of an incidental information that is present when the event occurs. For people with PTSD, these incidental memories can trigger anxiety attacks long after the event has occurred. Previous research suggested that increases in synaptic strength in creating associative and non-associative memories share common properties, so selectively eliminating non-associative synaptic memories would not be possible, because for any one neuron, a single mechanism would be responsible for maintaining all forms of synaptic memories, meaning both associative and non-associative.
The new study tested that hypothesis by activating two stimulating neurons connected to a single motor neuron of the marine snail Aplysia--one sensory neuron to induce an associative memory and the other to induce a non-associative memory. By measuring the strength of each connection, the researchers discovered 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. Each memory could be erased without affecting the other by blocking one of the PKM molecules.
Though the research is still well short of human trials, the results of this study are likely to point to human applications. Though we are dramatically different at the organ and system level, animals are very similar at the cellular level, including the structure and function of the neuron. The results could be useful for the purposes of understanding human memory because vertebrates have similar versions of the Aplysia PKM proteins that are involved in the formation of long-term memories.
As explained by Jingyuan Hu, an associate research scientist in the Department of Psychiatry at CUMC and co-author of the paper, "Memory erasure has the potential to alleviate PTSD and anxiety disorders by removing the non-associative memory that causes the maladaptive physiological response. 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."
The research might allow scientists to eliminate the non-associative memories without harming the associative memories, which can help people with PTSD and anxiety attacks. One focus of the research is "to develop strategies to eliminate problematic non-associative memories that may become stamped on the brain during a traumatic experience, without harming associative memories," said Dr. Schacher.
Samuel Schacher, Professor of Neuroscience at CUMC and co-author of the paper, gives an example: "If you are walking in a high-crime area and you take a shorcut 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," according to the CUMC press release of the study. In this example, fear of dark alleys is an associative memory that provides important information while fear of mailboxes is an incidental, non-associative memory that is not directly related to the traumatic event.
