Wiping Out Memories

The subunit composition of AMPA receptors at lateral amygdala synapses changes after the acquisition of associative fear. Inhibition of fear responses can be unexpectedly reversed even when a subject is perfectly safe. This can lead to inappropriate reactions to a fear-associated trigger, such as a bright light or loud noise. This type of reaction appears to underpin posttraumatic stress disorder, but there is little understanding of when training to inhibit fear may fail or succeed. Using a combination of electrophysiology and behavioral training in mice, Clem and Huganir observed that fear conditioning increased synaptic transmission by calcium-permeable AMPA receptors into the part of the brain that controls emotional responses (the amygdala). This effect lasted for about a week, during which the fearful memories could be erased if the animals were trained to reduce conditioned fear responses. Postmortem brain slices showed that the fear-induced synaptic changes also reversed, except in transgenic mice with a mutant subunit of the AMPA receptor. R. L. Clem, R. L. Huganir, Calcium-permeable AMPA receptor dynamics mediate fear memory erasure. Science 330, 1108–1112 (2010). [Abstract] [Full Text]