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Mental disorders

Anxiety Disorders

Alzheimer’s-type Dementia

Help Lien : Anxiety disorders Lien : Surviving stress Lien : Attenuation of frontal asymmetry in pediatric posttraumatic stress disorder.
Lien : Proton Magnetic Resonance Spectroscopy of the Hippocampus and Occipital White Matter in PTSD: Preliminary Results Lien : Functional brain imaging Lien : Moody Brains
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Tool Module: Brain Imaging Brain Imaging

The source of many anxiety disorders is a conditioned fear. We speak of a conditioned fear when an object or situation that in itself is neutral becomes associated with something that is threatening , thus triggering a fear reaction. The brain structure at the centre of this process is the amygdala.

But this association is not necessarily durable, because there is another process, called extinction, that can overcome it. Extinction can occur spontaneously over time, if the association between the neutral stimulus and the fear is not reinforced. Or it can be achieved deliberately, through rational efforts in the cerebral cortex (in the course of psychotherapy, for example).

Though extinction may thus be a process that the cortex applies “from the top down” to soothe the fears conditioned by the amygdala, these fears may in fact never be fully erased during an individual's lifetime. There is much evidence supporting this hypothesis, some of it right in the circuits of the amygdala itself. Moreover, it is thought to be precisely these circuits that psychotherapy addresses, by increasing the repertoire of soothing messages that can be sent down to them from the cortex.

Expérience : Study May Explain Fear Response in PTSD


The various anxiety disorders involve many different areas of the brain. These areas reflect both the uniqueness of each of these disorders and the features that they have in common.


The amygdala, for example, plays a central role in anxiety disorders. This structure in the limbic system warns us when a danger is present in our environment and triggers the fear reaction and then the fight or flight reaction to get us out of it.


It is therefore no surprise that the central part of the amygdala seems to play an important role in anxiety disorders that involve specific fears, such as phobias. Researchers have also observed that a group of very anxious children had larger amygdalas, on average, than a group of normal children.


Source: Jacob L. Driesen, Ph.D.


  The hippocampus is another essential limbic structure that specializes in encoding information. Because all old memories depend on the hippocampus, it would be suprising if this structure were not involved in anxiety disorders that are generated by memories of painful experiences, such as post-traumatic stress disorder (PTSD).

And in fact, studies do show that people who have suffered the stress of incest or military combat have a smaller hippocampus. This atrophy of the hippocampus might explain why such people experience explicit memory disturbances, flashbacks, and fragmentary memories of the traumatic events in question.

Source: J. Douglas Brenner

Left: Functional magnetic resonance image (MRI) of the hippocampus of a normal child.
Right: Functional MRI of a child who has suffered sexual abuse; the volume of the hippocampus is reduced significantly.

In addition to these differences in the size of various brain structures, abormally high or low activity in a particular region of the brain, as revealed by brain imaging, may be another kind of anomaly that results in anxiety disorders.

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