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Mental disorders
Depression and Manic Depression
Anxiety Disorders
Alzheimer’s-type Dementia

Help Lien : Is the amygdala the key to control of the emotional memories that trigger irrational panic?

Some researchers believe that the amygdala may contain certain circuits that are pre-wired but not normally connected to the circuits that trigger emotional responses. Thus a traumatic event (for example, a baby monkey seeing its mother be afraid of a snake ) might not create a fear circuit from scratch, but might simply connect one that was already there.

We can thus imagine how some people's brains, because of early influences or genetic predispositions (such as especially sensitive pre-wired circuits) might react to certain traumatic experiences by developing phobias.

It would also seem that fear extinction depends on the same synaptic learning mechanism as fear conditioning in the amygdala or explicit long-term memory in the hippocampus: the activation of NMDA receptors. Thus, if the NMDA receptors are blocked, the process of extinction is disturbed, and the amygdala does not learn how to inhibit an especially anxiety-producing memory.


It was long believed that a particular sensation, emotion, or thought represented activity in one particular part of the brain, relatively isolated from any others. But increasingly, this belief is yielding to a more sophisticated view: that neural representations result from the activity of multiple circuits, distributed across various parts of the brain and interacting dynamically.

In the case of anxiety disorders, the locus of the conditioned fears that cause the various excessive manifestations of anxiety seems to be the numerous neural connections among the various nuclei of the amygdala.

But the part of the brain that can potentially relieve these fears embedded deep in the amygdala is the vast surface of the cortex, where rational thinking takes place. Because of its great plasticity, the cortex can inhibit sub-cortical structures sufficiently to contain fears that have become inappropriate. This is the process of extinction that is applied in behavioural therapy.

Many experiments, by researchers such as Quirk, Repa, and LeDoux, support this model. These scientists recorded electrophysiological activity in the neurons of the amygdalae of rats that were subjected to a sound that produced a conditioned fear. The recordings showed a dramatic increase in the electrical response of these neurons when the sound was generated. And this increased activity was indeed reversed after the conditioning was extinguished.

By making recordings in different cells simultaneously, these researchers were also able to observe the relationships that these cells maintained with one another. These recordings showed that conditioning increased the coupling between certain neurons, so that the probability of two neurons' firing at the same time was greatly increased. But the most interesting finding was that for some cells, this coupling was not diminished when the conditioning was extinguished.

Conditioning thus seems to create special “assemblies of neurons” in the amygdala, many of which are resistant to extinction. Though this hypothesis is still speculative, this experiment also supports other observations indicating that the traces of conditioned fears in the amygdala are permanent and that inhibition by the cortex is the mechanism responsible for extinguishing them.

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