Severe Trauma May Damage The Brain as Well as the Psyche
Published: August 1, 1995
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Studies in rats and primates suggest that glucocorticoids, the equivalent of cortisol in other species, "may be neurotoxic to the hippocampus at the massive levels that are released under extreme stress or during trauma," said Dr. Robert Sapolsky, a neuroscientist at Stanford University. "I'm talking about the levels you would see in a zebra running from a lion, or a person fleeing a mugger -- a real physical life-and-death crisis -- if it is repeated again and again as time goes on."
During such moments of crisis, the body engages in a kind of biological triage, suppressing less pressing functions like ovulation, immune-system reactions and growth, shunting its resources to the muscles needed to survive the immediate danger.
Cortisol is a major means the body uses, with adrenaline, to arouse itself so quickly; its action, for example, triggers an increase in blood pressure and mobilizes energy from fat tissue and the liver.
"The dark side of this picture is the neurological effects," said Dr. Sapolsky. "It's necessary for survival, but it can be disastrous if you secrete cortisol for months or years on end. We've known it could lead to stress-exacerbated diseases like hypertension or adult onset diabetes. But now we're finding the hippocampus is also damaged by these secretions."
Studies in animals show that when glucocorticoids are secreted at high levels for several hours or days, there is a detectable effect on memory, though no neuronal death. But with sustained release from repeated stress, "it eventually kills neurons in the hippocampus," said Dr. Sapolsky. "This has been shown solidly in rats, with the cell biology well understood."
A parallel effect has long been known among patients with Cushing's disease, a hormonal condition in which tumors in the adrenal or pituitary glands or corticosteroid drugs used for a prolonged time cause the adrenal glands to secrete high levels of a hormone called ACTHm and of cortisol. Such patients are prone to a range of diseases "in any organ with stress sensitivity," including diabetes, hypertension and suppression of the immune system, said Dr. Sapolsky.
Cushing's patients also have pronounced memory problems, especially for facts like where a car was parked. "The hippocampus is essential for transferring such facts from short-term to long-term memory," said Dr. Sapolsky.
In 1993, researchers at the University of Michigan reported that magnetic resonance imaging had shown an atrophy and shrinkage of the hippocampus in patients with Cushing's disease; the higher their levels of cortisol, the more shrinkage.
In an apparent paradox, low levels of cortisol in post-trauma victims were found in a separate research report, also in the July issue of The American Journal of Psychiatry. Dr. Rachel Yehuda, a psychologist at Mount Sinai Medical School in New York City, found the lower levels of cortisol in Holocaust survivors who had been in concentration camps 50 years ago and who still had post-traumatic symptoms.
"There are mixed findings on cortisol levels in trauma victims, with some researchers finding very high levels and others finding very low levels," said Dr. Sapolsky. "Biologically speaking, there may be different kinds of post-traumatic stress."
In a series of studies, Dr. Yehuda has found that those post-trauma patients who have low cortisol levels also seem to have "a hypersensitivity in cell receptors for cortisol," she said. To protect itself, the body seems to reset its cortisol levels at a lower point.
The low cortisol levels "seem paradoxical, but both too much and too little can be bad," said Dr. Yehuda. "There are different kinds of cells in various regions of the hippocampus that react to cortisol. Some atrophy or die if there is too little cortisol, some if there is too much."
Dr. Yehuda added, "In a brain scan, there's no way to know exactly which cells have died."
To be sure that the shrinkage found in the hippocampus of trauma victims is indeed because of the events they suffered through, researchers are now turning to prospective studies, where before-and-after brain images can be made of people who have not yet undergone trauma, but are at high risk, or who have undergone it so recently that cell death has not had time to occur.
Dr. Charney, for example, is planning to take M.R.I. scans of the brains of emergency workers like police officers and firefighters and hopes to do the same with young inner-city children, who are at very high risk of being traumatized over the course of childhood and adolescence. Dr. Pitman, with Dr. Yehuda, plans a similar study of trauma victims in Israel as they are being treated in emergency rooms.
Dr. Yehuda held out some hope for people who have suffered through traumatic events. "It's not necessarily the case that if you've been traumatized your hippocampus is smaller," she said. She cited research with rats by Dr. Bruce McEwen, a neuroscientist at Rockefeller University, showing that atrophied dendritic extensions to other cells in the hippocampus grew back when the rats were given drugs that blocked stress hormones.
Dr. Sapolsky cited similar results in patients with Cushing's disease whose cortisol levels returned to normal after tumors were removed. "If the loss of hippocampal volume in trauma victims is due to the atrophy of dendrites rather than to cell death, then it is potentially reversible, or may be so one day," he said.
Photos: In an M.R.I. scan of a patient with combat-related post-traumatic stress disorder, both the left and and the right hippocampus regions showed decreased volume compared with the same regions in a similar veteran who had not suffered any combat trauma. (Dr. J. Douglas Bremner)