A New Technique Could Erase Painful Memories -- Or Bring Them Back
By using pulses of light, researchers at the UC San Diego School of Medicine have produced, erased, and restored fearful memories in rats. It's a finding that could have profound implications for people struggling with neurodegenerative and anxiety disorders.
The study, though not the first to implant a memory in a rodent, is the first to selectively remove a memory — in this case, a conditioned fear response — and then predictably reactivate it by stimulating nerves in the brain at frequencies known to weaken and strengthen the connections between synapses. It's probably the most sophisticated memory engineering experiment done to date.
What's more, the study confirms a long-standing theory about how memories are made and stored in the brain. The experiment suggests that the weakening of specific nerve cells likely disassembles neuronal circuits, resulting in the inactivation of a memory. This confirmation hints at future therapies in which neuroscientists can take control of runaway emotional memories in mental illnesses, such as post-traumatic stress disorder.
Let There Be Light
Neuroscientists theorize that memories are formed when connections between neurons are strengthened — a process facilitated by mechanisms such as long-term potentiation (LTP) and long-term depression (LTD). But this has been difficult to demonstrate in the lab. This latest study, which was conducted by Roberto Malinow of the University of California, San Diego, Roger Tsien of NIH's National Institute on Neurological Disorders and Stroke (NINDS), and other UCSD colleagues, proves that a causal link exists between these synaptic processes.
It was a confirmation made possible by the burgeoning field of optogenetics — a technique in which a gene is delivered to the brain cell of an animal using a special virus. Once delivered, the gene produces a series of light-responsive proteins which can either be activated or disabled by fiber optic cables inserted into the brain. To date, neuroscientists have used the technique to induce sensations, memories, and behavioral changes in mice and monkeys. In the new experiment, pulses of fibre optic light were used to both remove and reactivate conditioned responses in rats.
http://i.kinja-img.com/gawker-media/...eizcgzc9yi.png
Engineering Memory
The first stage of the experiment was to produce a conditioned fear response in the rats. The scientists did so by optically stimulating a group of nerves in rats' brains that had been genetically modified to make them sensitive to light. At the same time, the researchers delivered an electric shock to the rats' feet. The rats thus learned to associate the optical nerve stimulation with pain, thereby triggering fearful behavioral responses.
Subsequent analysis showed that the resulting chemical changes were consistent with synaptic strengthening.
