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Re: hippocampus, thalamus amygdala EscherDementian

Posted by noa on March 13, 2004, at 8:51:59

In reply to hippocampus, thalamus amygdala, posted by EscherDementian on March 13, 2004, at 5:11:28

I know that other babblers here will know more than me, but here is what I understand about the hippocampus and amygdala. (and PLEASE, if I've gotten something wrong, I hope one of the psychologists or scientists will correct me!!)

I think the thalamus is somehow involved in sensing danger signals. It sends a message to two parts of the brain about any danger signals it detects in the environment. The message pathway to the front of the brain, the thinking cortex, if you will, is a longer route than the pathway to the amygdala, which is like a mobilizer for reacting to danger (the 'flight/fight response'). So, the amygdala gets the flight-fight response going before the thinking part of the brain can analyze the danger signal. And, I think once the flight/fight gear is activated by the amygdala, if it is a strong flight fight response, it kind of short-circuits the cortex's ability to figure out what is going on from a reasoning, language oriented, problem solving sort of perspective because all those reaction chemicals are elevated (I think noradrenaline, cortisol, etc.)

I think that with chronic fear, the amygdala jumps in quickly no matter what level of danger is detected, and because the cortex is blocked by the stress hormones, it can't send back a message saying something like, "Hey, guys, this is just a little tiny potential danger signal but it is not really a threat because here are all the possible things I can do, say or think to put it in perspective and deal with it", or, "Hey guys, this resembles something that is a threat, but it isn't the same thing, so chill out".

The hippocampus, I think, helps to process experiences into memories. I think somehow if the amygdala has 'spoken louder' than the reasoning, language oriented parts of the brain, it affects the way memories are processed by the hippocampus, because the way the experience was processed is via flight-fight without being able to organize and make sense of and analyse the danger signal and organize a response that is proportional to the level of danger. I think that this is why some memories are processed as emotions and physical sensations rather than as a sequenced story memory of what really happened. Also, btw, if part of the flight fight response is dissociation, then the person really wasn't even fully present to remember what actually happened, but only has incomplete snapshots without a sequenced story.

Sapolsky, in his book, "Why Zebras Don't Get Ulcers" says that the flight fight response is designed for short-term intense life threatening situations (zebra running from lion)where the physical and neurological aspects of flight-fight are adaptive to the situation and the situation is acute rather than chronic. In chronic severe stress, the flight fight chemicals take their toll on the body (eg, ulcer) and brain (eg, apparently, the neurochemicals of distress, when chronically present, cause the hippocampus to be smaller) over time and become less adaptive over time because, due to circumstances beyond their control, the child, for instance, can't flee or fight the source of danger.

In addition to Sapolsky's book, see Rita Carter's "Mapping the Mind".

I think all of this is one reason cognitive behavioral therapy is seen as effective--it helps build up the thinking brain's role in processing experiences.



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