Neural plasticity in the amygdala: implications for stress disorders

Some experiences are memorable, others forgettable. How does a particular experience leave its mark as a memory in the brain? For more than a century, the search for a biological basis of memory formation has centered on the synapse, the junction where information is passed from one brain cell 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 over the past few decades, we know little about why some memories last for a long time while others fade away. My laboratory is 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 has contrasting effects on different types of memories. Stress impairs memories of facts and events, which depend on synaptic plasticity in a brain structure called the hippocampus. In contrast, stress greatly amplifies emotional memories, which are processed by another structure called the amygdala. But little is known about the neural basis for this contrast.

Therefore, we study the effects of stressful experiences on synapses, cells and microcircuits in the hippocampus and amygdala, by using a combination of behavioral, neuroanatomical, computational, genetic engineering and electrophysiological techniques. Using this strategy, we have identified several novel neural correlates of stress-induced plasticity in the amygdala, which are strikingly different from those observed in the hippocampus. Our findings suggest that prolonged stress leaves its mark by enhancing both the physiological and structural basis of synaptic connectivity in the amygdala, thereby triggering the emotional symptoms observed in stress-related psychiatric disorders.