An excerpt from Synaptic Self: How Our Brains Become Who We Are
by Joseph LeDoux
Fear conditioning by the amygdala, as I’ve said many times, is an implicit form of learning, one that does not require conscious participation. During any experience in which we are awake and alert, however, working memory will be aware of what is going on, and if what is going on is significant, the executive will direct the storage of information about the situation in the explicit memory system. We are thus later able to consciously recall (retrieve into working memory) those aspects of the experience that were stored explicitly. While this is true of any kind of explicit memory, explicit memories about emotion are unique.
Explicit memories established during emotional situations are often especially vivid and enduring, and for this reason are called flashbulb memories. The classic example is that most baby-boomers know where they were and what they were doing when they heard the news that JFK had been shot. But we are all aware of our own daily experiences that we remember particularly well those things that are the most important to us, those things that arouse our emotions. Emotions, in short, amplify memories.
Studies by Jim McGaugh and colleagues spanning several decades have implicated the amygdala in the emotional amplification of explicit memory. During emotional arousal, outputs of the central amygdala trigger the release of hormones from the adrenal gland that return to the brain. The amygdala, it turns out, is an important target of such feedback. The feedback consists of the direct action of body hormones (like cortisol released from the adrenal cortex) on amygdala neurons, as well as indirect actions whereby hormones (like epinephrine and norepinephrine released from the adrenal medulla) interact with nerves that travel from the body into the brain and ultimately reach and influence neural activity in the amygdala. By way of its connections with the hippocampus and other regions of the explicit memory system, the amygdala then modulates (strengthens) the consolidation of explicit memories being formed during emotional arousal. Later, the memories are more easily retrieved, and the details of the original experience are more vivid. Thus, in addition to storing implicit memories about dangerous situations in its own circuits, the amygdala modulates the formation of explicit memories in circuits of the hippocampus and related areas. Studies in recent years led by Larry Cahill and Benno Roozendaal in McGaugh’s lab have helped to refine the latter conclusion.
According to the mood congruity hypothesis, memories are more easily retrieved when the emotional state at the time of memory formation matches the state at the time of retrieval. For example, we are more likely to remember sad than happy events when depressed. Perhaps amygdala activation during retrieval facilitates remembrance by re-creating, at least in part, the emotional state (the state of the brain resulting from amygdala activation, and all its consequences, as discussed above) that occurred during the original experience—the more similar the pattern of activation is during learning and retrieval, the more efficient retrieval is likely to be…
Joseph LeDoux is a professor and a member of the Center for Neural Science and Department of Psychology at NYU and a member of the National Academy of Science. His work is focused on the brain mechanisms of emotion and memory. In addition to articles in scholarly journals, he is author of Synaptic Self: How Our Brains Become Who We Are, The Emotional Brain: The Mysterious Underpinnings of Emotional Life, and the upcoming book, Anxious: Finding New Ways to Understand and Treat Fear and Anxiety (Viking 2015).
*All of the excerpts on my blog are from books that have stayed with me for some reason—because the concept was awe inspiring, changed how I view the world, was beautifully expressed, or all three. I personally curate all of the book excerpts, and I always obtain the author’s final approval before posting their work on my blog.