There is now considerable evidence that severe psychological trauma, and particularly childhood trauma, has long-lasting impact on the brain. Since the time of Freud, psychotherapists have been aware of the severe and persistent psychological damage caused by traumatic experiences, but neuroscience is now catching up with the clinicians. Trauma triggers the body’s stress response, mediated through the HPA axis. Over-activation of the HPA axis, as can occur with chronic trauma such as child abuse, dulls its flexibility, sort of like a rubber band that has been stretched out of shape.

This results in people with either overactive or underactive stress responses. Frequently, they have both. When the stress response is underactive, people can be somewhat dissociated, as if they are not processing what is going on around them. When the stress response is overactive, people will be hyper-reactive to any possible threat. Another set of studies has suggested that there is a reduced volume in the hippocampus in people with trauma histories. This may relate to the distortions of memory that often accompanies trauma.