[AdmSmith]

The similarities between these regions of the human and rodent brain are remarkable,” Redei explained. “The hippocampus and amygdala are part of the so-called ancient lizard brain that controls survival and are the same in even primitive organisms.”

True, and my guess is that the key is in the hippocampus (+ long term stress):

Such atrophy is centered in a brain region called the hippocampus. This structure plays a critical role in learning and memory, and the magnitude of the hippocampal volume loss (nearly 20% in some reports;) helps explain some well-documented cognitive deficits that accompany major depression. These were careful and well-controlled studies, in that the atrophy was demonstrable after controlling for total cerebral volume and could be dissociated from variables such as history of antidepressant treatment, electroconvulsive therapy, or alcohol use. Moreover, more prolonged depressions were associated with more severe atrophy.

http://www.pnas.org/content/98/22/12320.full

A possible explanation:

Because synapses have the potential for rapid response, synapse loss probably underlies the rapid deterioration of mood that depressed patients sometimes experience, said Hajszan. Thus, it is possible to elevate mood rapidly by generating new hippocampal synapses, which is attainable by certain drugs we are testing.

http://www.scientificblogging.com/news_releases/stress_unravels_brain_structure_study

[nuconvert]

Interesting. Thanks

[SunkenCiv]

Thanks AdmSmith.