The Amygdala and Unconscious Memories

Neuroscientist
The amygdala is responsible for implicit memories, but these are different from what Freud called the unconscious.
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TRANSCRIPT

Question: Can we think of the amygdala as the seat of what Freud called the unconscious?

Joseph LeDoux: I think it’s a distraction because... I mean, it’s true in the sense that the hippocampus is necessary to have a conscious recollection of some past event, and the amygdala participates in unconscious memory. But we shouldn’t really taint it with the Freudian concepts because that adds a lot of baggage.  

The amygdala is an unconscious processor because it’s just not connected with the conscious system.  It’s kind of like by default unconscious as opposed to being in the Freudian sense of unconscious something that was conscious, but was too anxiety-provoking and therefore shipped to the unconscious.  The amygdala gets direct sensory information and it learns and stores information on its own, and that information that’s stored then controls emotional responses.  The connectivity is hardwired, so one way to think about it is that a rat will respond to a cat without any learning by freezing, raising its blood pressure and heart rate and respiration and releasing stress hormones.  But it will also respond to a stimulus associated with a cat and have the same responses.  

So you don’t learn how to be afraid, your amygdala doesn’t have to learn what to do, it learns what to do it in response to.  So it learns what stimuli it should respond to.  So it’s learning and memory in that sense that we call an implicit kind of memory where you don’t have to have any conscious involvement.  

Whereas, the hippocampus is necessary to have a conscious memory.  So, yes, they do participate in conscious and unconscious memories, but not in the Freudian sense.  But there’s a whole other side of the amygdala’s role in memory, which is that when the amygdala is activated and all of those hormones and other things happened to get released, that provides information that feeds back to parts of the brain, like the hippocampus and allows them to store their memories in a much more efficient and strong way.  So we know that emotional memories are stored more vividly than other kinds of memories.  It used to be thought that they were more accurate, but in fact now we know that they are not more accurate, they’re just more vivid and strong in the personal sense.  But they can be highly inaccurate.  This is shown by studies of natural disasters and so forth, well not always so natural.  But like the Space Challenger Shuttle... or the shuttle, Space Shuttle Challenger explosion, a lot of people witnessed that and they were studied almost immediately by psychologists who made notes of exactly what their responses, what they were experiencing at the time and then a year later, they were surveyed again and the responses were completely different from what they remembered originally and then several years later it completely changed again.  

So what we remember is not necessarily what we experienced originally.  So the accuracy of those memories changes over time, but their strength in terms of your subjective feeling that it was a really powerful experience is there.

Recorded on September 16, 2010
Interviewed by Max Miller