BioEd Online

A bout of post-traumatic stress disorder (PTSD) may do damage to the brain that kick-starts memory problems, scientists have discovered. Even patients who had recovered from a period of stress started to get age-related memory difficulties about a decade earlier than non-traumatized people, they report.

Post-traumatic stress, a condition that can cause patients to feel physical pain on remembering a traumatic event, is known to have a number of effects on the mind and body. One of the side effects is that patients tend to be forgetful, unable to remember a story or a list of words after they've heard it, for example. This problem, which could come from emotional distraction and an inability to concentrate, can interfere with everyday tasks.

Rachel Yehuda and her team at the Mount Sinai School of Medicine in New York decided to investigate further the link between PTSD and memory problems, by looking at what happens to patients as they age. Their study, due to be published in Biological Psychiatry¹, looks at three groups of people: Holocaust survivors with continued PTSD, survivors who had recovered from their trauma, and a control group who had not lived through the Holocaust and had never had PTSD.

The researchers looked at the study participants' ability to remember associations between common words such as 'desk and chair', a task that is known to become more difficult as we age. They tested their participants at the age of 67, and again at 72.

Those who had PTSD, even if they had subsequently recovered, could only come up with answers for half of the questions by the age of 72, a score that's usually expected from those over 80 years old. And they had showed a marked deterioration in scores from when they were 67. Those who had not had a trauma consistently got most, or all, of the questions right at both ages.

Having PTSD early in life seems to set up future problems, says Yehuda. "It's like getting sunburnt at 15 and developing melanoma later."

Stressed out

Researchers aren't sure how this might happen. Some think that stress hormones called glucocorticoids, which erupt in the body after a traumatic event such as fighting in a war, attack the hippocampus, a brain area that is key for memory. Some studies have shown the hippocampus of PTSD patients being unusually small, perhaps because it has been eaten away by stress hormones.

Others think that people with a naturally small hippocampus may be predisposed to both memory problems and PTSD. Perhaps it isn't trauma that shrinks this part of the brain, they say, but a small hippocampus that increases the likelihood of a stress disorder after a trauma.

There's another possible explanation: perhaps some other factor, such as diet, was very different between the Holocaust survivors and the control group, says Janet Leathem, an expert in PTSD and memory at Massey University in Wellington, New Zealand. The study didn't look at nutrition or weight loss in the Holocaust survivors, and this could be linked to their memory problems now.

But Yehuda thinks it is stress that's to blame. She points out that not all of the cognitive functions were worse in the Holocaust survivors. The ability to learn and repeat back a list of words, for example, a skill linked to the pre-frontal cortex, was actually better in patients who had recovered from PTSD, as though their brain was compensating for difficulties in the hippocampus.

"Ageing and trauma will nibble away at memory performance but the brain will be able to compensate to a point," says Ruben Gur, an expert in brain and behaviour at the University of Pennsylvania in Philadelphia.

The team's next steps are to look at soldiers who fought in wars to see whether they show the same pattern of decline. They are also going to look at young people who have been through trauma and follow them up later in life.

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