Hippocampal and Amygdalar Volumes in Dissociative
Identity Disorder (Please note that Richard Lowenstein, my attending physician at Sheppard Pratt trauma clinic, is noted numerous times in the "reference" section at the bottom of the article):
http://userwww.service.emory.edu/~jdbremn/papers/DID_MRI.pdf
Definition of Hippocampus and how it relates to long term stress (See Amygdala definition below this):
The hippocampus contains high levels of
glucocorticoid receptors, which make it more vulnerable to long-term
stress than most other brain areas.
[69] Stress-related steroids affect the hippocampus in at least three ways: first, by reducing the excitability of some hippocampal neurons; second, by inhibiting the genesis of new neurons in the dentate gyrus; third, by causing atrophy of dendrites in pyramidal cells of the CA3 region. There is evidence that humans who have experienced severe, long-lasting traumatic stress, show atrophy of the hippocampus, more than of other parts of the brain.
[70] These effects show up in
post-traumatic stress disorder, and they may contribute to the hippocampal atrophy reported in
schizophrenia and
severe depression. A recent study has also revealed atrophy as a result of depression, but this can be stopped with anti-depressants, even if they are not effective in relieving other symptoms.
[71] Hippocampal atrophy is also frequently seen in
Cushing's syndrome, a disorder caused by high levels of
cortisol in the bloodstream. At least some of these effects appear to be reversible if the stress is discontinued. There is, however, evidence mainly derived from studies using rats that stress shortly after birth can affect hippocampal function in ways that persist throughout life.
[72]
http://en.wikipedia.org/wiki/Hippocampus
Amaygdala definition:
A variety of data shows the amygdala has a substantial role in mental states, and is related to many
psychological disorders. Some studies have shown children with anxiety disorders tend to have a smaller left amygdala. In the majority of the cases, there was an association between an increase in the size of the left amygdala with the use of
SSRI's (antidepressant medication) or psychotherapy. The left amygdala has been linked to social anxiety, obsessive and compulsive disorders, and post traumatic stress, as well as more broadly to separation and general anxiety.
[26] In a 2003 study, subjects with
borderline personality disorder showed significantly greater left amygdala activity than normal control subjects. Some borderline patients even had difficulties classifying neutral faces or saw them as threatening.
[27] Individuals with
psychopathy show reduced autonomic responses, relative to comparison individuals, to instructed fear cues.
[28] In 2006, researchers observed
hyperactivity in the amygdala when patients were shown threatening faces or confronted with frightening situations. Patients with more severe
social phobia showed a correlation with increased response in the amygdala.
[29] Similarly, depressed patients showed exaggerated left amygdala activity when interpreting emotions for all faces, and especially for fearful faces. Interestingly, this hyperactivity was normalized when patients went on
antidepressants.
[30] By contrast, the amygdala has been observed to respond differently in people with
bipolar disorder. A 2003 study found that adult and adolescent bipolar patients tended to have considerably smaller amygdala volumes and somewhat smaller
hippocampal volumes.
[31] Many studies have focused on the connections between the amygdala and
autism.
[32] Additional studies have shown a link between the amygdala and
schizophrenia, noting that the right amygdala is significantly larger than the left in schizophrenic patients.
[33] Studies in 2004 and 2006 showed that normal subjects exposed to images of frightened faces or faces of people from another race will show increased activity of the amygdala, even if that exposure is
subliminal.
[34][35] However, the amygdala is not necessary for the processing of fear-related stimuli, since persons in whom it is bilaterally damaged show rapid reactions to fearful faces, even in the absence of a functional amygdala.
[36]
http://en.wikipedia.org/wiki/Amygdala