The Neurobiology of Trauma
During exposure to a stressor, the brain initiates a cascade of responses. Glucocorticoids are released to mobilize energy, increase cardiovascular activity, and slow down unnecessary physiological processes. Chronic exposure to extremely high levels of glucocorticoids can seriously damage neurons; this is most evident in the hippocampus which contains a high concentration of glucocorticoid receptors. Various animal studies have shown permanent loss of glucocorticoid receptors in the hippocampus as well as significant damage to the hippocampal neurons, with resulting hippocampal degeneration.
Studies using magnetic resonance imaging (MRI) found reduced hippocampal volume in adults with PTSD. In their combat veteran research, Bremner et al. (1995) compared 26 Vietnam veterans with PTSD to 22 normal veterans, similar in age, sex, race, years of education, socioeconomic status, body size, and years of alcohol abuse. Combat veterans with PTSD had a statistically significant 8% smaller right hippocampal volume and a statistically insignificant 4% smaller left hippocampal volume.
In a similar study with adult survivors of childhood abuse, Bremner et al. (1996) found that those survivors with PTSD had a 12% smaller left hippocampal volume and a statistically insignificant 5% smaller right hippocampal volume. It is not known why persons traumatized as adults had smaller right hippocampal volume and those traumatized as children had smaller left hippocampal volume. The researchers suggest that larger sample sizes, with increased power, might find smaller volumes for both right and left hippocampal volumes. Another possibility is that there is a true difference in patients with early trauma, and that early trauma may interfere with brain development.
Diminished hippocampal size may be either a consequence of trauma exposure or a risk factor for the development of psychiatric complications following trauma exposure. Dysfunction of the hippocampus may be related to the fragmentation of memory that occurs with PTSD and to dissociation.
Similar findings were found by Stein, Koverola, Hanna, Torchia, & McClarty (1997) who measured hippocampal volume using the MRI in 21 women who reported being severely sexually abused in childhood. They compared these subjects to a control group of 21 socio-demographically similar women without abuse histories. A statistically significantly 5% smaller left hippocampal volume was found in the women who reported sexual victimization in childhood, as well as a statistically insignificant smaller right hippocampal volume. Left-sided hippocampal volume correlated highly (r = -0.73) with dissociative symptom severity. Stein et al. suggest that the relationship between symptom severity and hippocampal volume indicates that mesial temporal lobe dysfunction may directly mediate certain aspects of PTSD and dissociative disorder symptomatology.
Possible hippocampal degeneration is only one aspect of the complex picture. Studies on the physiological effects of trauma have found profound and substantial effects within multiple interconnected neurobiologic systems. Exposure to extreme or chronic trauma related stressors can result in abnormal patterns of neurotransmitter and hormonal activity, and in permanent changes in neuronal differentiation and organization. Neurobiological effects are evident in brain stem dysregulation, alterations within the central nervous system, irregularities in cortical function, alterations within catecholamine systems, and dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-pituitary-thyroid axis.
Since these effects are pervasive, powerful, and occasionally permanent even for adults, it is apparent that childhood trauma can have a massive impact on the developing brain, with its high levels of plasticity. The child's brain is structured and neuronally organized by experience. There are substantial implications for all aspects of children's development, with potential deficits and impairment in emotional, behavioral, cognitive, and social functioning.
Bremner, J. D., Krystal, J. H., Charney, D.S., & Southwick, S. M. (1996).
Neural mechanisms in dissociative amnesia for childhood abuse: Relevance to the current controversy surrounding the "false memory syndrome."
American Journal of Psychiatry, 153 (7), 71-82.
Bremner, J. D., Randall, P., Scott, T. M., Bronen, R. A., Seibyl, J. P., Southwick, S. M., Delaney, R. C., McCarthy, G., Charney, D. S., & Innis, R. B. (1995).
MRI-based measurements of hippocampal volume in patients with combat-related posttraumatic stress disorder.
American Journal of Psychiatry, 152 (7), 973-981
Bremner, J. D., Randall, P., Vernetten, E., Staib, L., Bronen, R. A., Mazure, C., Capelli, S., McCarthy, G., Innis, R. B., & Charney, D. S. (in press).
MRI-based measurement of hippocampal volume in posttraumatic stress disorder related to childhood physical and sexual abuse: A preliminary report.
Stein, M. B., Koverola, C., Hanna, C., Torchia, M. G., & McClarty, B. (1997).
Hippocampal volume in women victimized by childhood sexual abuse.
Psychological Medicine, 27 (4), 951-959.