Silent Synapses Speak Up In the Amygdala: “Good Plasticity” In a “Bad Neighborhood”
Sumantra Chattarji, National Centre for Biological Sciences
Some experiences are memorable, others forgettable. How does a particular experience leave its mark as a memory in the brain? The search for a biological basis of memory formation has centered on the synapse, the junction where information is passed from one neuron to another. The remarkable ability of synapses to change in response to experience, a property described as “synaptic plasticity”, is believed to mediate long-term storage of information in the brain. Although common cellular and molecular mechanisms underlying synaptic plasticity and memory have been identified, we know little about why some memories last for a long time while others fade away. I am interested in understanding why memories of emotional events are often very powerful and persistent. Why do war veterans or victims of severe stress continue to have vivid flashbacks of traumatic events from their past, while their cognitive abilities diminish? Stress disorders bring these questions into sharp focus because chronic stress impairs memories of facts and events, which depend on synaptic plasticity in a brain area called the hippocampus. In contrast, stress amplifies emotional memories, which are processed by the amygdala.
But little is known about the neural basis for this contrast. Therefore, we study the effects of stressful experiences on synapse and cells in the hippocampus and amygdala, by using behavioral, neuroanatomical, genetic engineering and electrophysiological techniques. Using this strategy, we have identified novel neural correlates of stress-induced plasticity in the amygdala that are strikingly different from those observed in the hippocampus. Our findings suggest that prolonged stress leaves its mark in the amygdala by forming new synapses with enhanced capacity for subsequent potentiation, thereby creating an ideal synaptic substrate for emotional symptoms observed in stress disorders.
1. Taming Stress, Robert Sapolsky, Scientific American, 2003.