From J. Douglas Bremner, M.D
The invisible epidemic of childhood abuse and other psychological traumas and stressors represents a major public health problem in our society today. Childhood sexual abuse alone affects 16% of women (about 40 million) in the U.S.A. (including rape, attempted rape, or molestation) at some time before their 18th birthday.1
Childhood abuse is the most common cause of posttraumatic stress disorder (PTSD) in women, which affects 8% of the population at some time in their lives,2 although there are a range of other types of psychological trauma that can also lead to symptoms of chronic PTSD, including car accidents, combat, rape and assault. Some of the symptoms of PTSD, which include intrusive memories, nightmares, flashbacks, increased startle and vigilance, social impairment and problems with memory and concentration, may be related to the effects of extreme stress on the brain.3,4
Individuals with a history of exposure to childhood abuse or combat had a reduction in volume of a brain area involved in learning and memory called the hippocampus, which is felt to be related to stress, with associated deficits in hippocampal-based learning and memory.5 Children under stress develop impairments in academic achievement that are specifically related to the development of PTSD. Other symptoms, including fragmentation of memory, intrusive memories, flashbacks, dissociation and pathological emotions, may also be related to hippocampal dysfunction6 and may explain delayed recall of childhood abuse.7 The hippocampus has important links to the medial prefrontal cortex, another brain area that mediates emotion and the stress response, dysfunction of which has also been implicated in PTSD.
Effects of psychological trauma on the hippocampus and memory
Childhood abuse and other extreme stressors can have lasting effects on brain areas involved in memory and emotion. The hippocampus is a brain area involved in learning and memory that is particularly sensitive to stress.8,9 As reviewed in greater detail by Bruce McEwen in other Cyberounds high levels of glucocorticoids (cortisol in the human) released during stress were associated with damage to neurons in the CA3 region of the hippocampus, and a loss of neurons and dendritic branching.10,11,12 Glucocorticoids disrupt cellular metabolism and increase the vulnerability of hippocampal neurons to excitatory amino acids like glutamate.13 Other neurochemical systems interact with glucocorticoids to mediate the effects of stress on memory and the hippocampus, including serotonin14 and brain-derived neurotrophic factor (BDNF).15,16 Stress also results in deficits in new learning that are secondary to damage to the hippocampus.17,18 Exciting recent research has shown that the hippocampus has the capacity to regenerate neurons and that stress inhibits neurogenesis in the hippocampus.19
Studies in animals showing glucocorticoid-mediated hippocampal toxicity and memory dysfunction with stress raised the question: Does early stress, such as childhood abuse, result in similar deficits in human subjects? With this in mind, we used neuropsychological testing to measure declarative memory function in PTSD. We selected measures that were validated in studies of patients with epilepsy to be specific probes of hippocampal function. These neuropsychological measures (including delayed paragraph recall and word list learning) were correlated with a loss of neurons in the hippocampus in patients who underwent surgical resection of the hippocampus for the treatment of epilepsy.20 We initially found verbal declarative memory deficits using similar measures in Vietnam combat veterans with PTSD.21
