PTSD: Biological perspective

Neurochemistry
PTSD displays biochemical changes in the brain and body, which are different from other psychiatric disorders such as major depression.

In PTSD patients, the dexamethasone cortisol suppression is strong, while it is weak in patients with major depression. In most PTSD patients the urine secretion of cortisol is low, at the same time as the catecholamine secretion is high, and the norepinephrine/cortisol ratio is increased. Brain catecholamine levels are low, and corticotropin-releasing factor (CRF) concentrations are high. There is also an increased sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis, with a strong negative feedback of cortisol, due to a generally increased sensitivity of cortisol receptors (Yehuda, 2001).

The response to stress in PTSD is abnormal with long-term high levels of norepinephrine, at the same time as cortisol levels are low, a pattern associated with facilitated learning in animals. Translating this reaction to human conditions gives a pathophysiological explanation for PTSD by a maladaptive learning pathway to fear response (Yehuda 2002). With this deduction follows that the clinical picture of hyperreactivity and hyperresponsiveness in PTSD is consistent with the sensitive HPA-axis.

Swedish United Nations soldiers serving in Bosnia and Herzegovina with low pre-service salivary cortisol levels had a higher risk of reacting with PTSD symptoms, following war trauma, than soldiers with normal pre-service levels (Aardal-Eriksson 2001).

Another possible factor in PTSD is that a persistence of depressive symptoms may be caused by an underlying biochemical disorder, associated with insulin resistance (dysglycemia), that can be treated by a hypoglycemic diet.

Neuroanatomy
In animal research as well as human studies, the amygdala has been shown to be strongly involved in the formation of emotional memories, especially fear-related memories. Neuroimaging studies in humans have revealed both morphological and functional aspects of PTSD. The amygdalocentric model of PTSD proposes that it is associated with hyperarousal of the amygdala and insufficient top-down control by the medial prefrontal cortex and the hippocampus. Further animal and clinical research into the amygdala and fear conditioning may suggest additional treatments for the condition.