Tokyo

Researchers studying the long-term effects of the 1995 sarin gas attack in the Tokyo underground have unearthed some intriguing clues about what controls different people's susceptibility to the psychological after-effects of shock.

Hidenori Yamasue, a psychiatrist at the University of Tokyo, has been looking at images of the brains of survivors of the attack. He found that of 25 survivors studied, the volume of an area of the brain known as the anterior cingulate cortex (ACC) was smaller, on average, in the nine who were diagnosed with post-traumatic stress disorder. The degree of size reduction correlated with the severity of the symptoms.

The finding, reported this week in the Proceedings of the National Academy of Sciences (100, 9039–9043; 2003), could help to clarify a difficult area of neuroscience. Several previous studies searching for a link between the size of a different area of the brain, the hippocampal region, and stress symptoms have produced inconclusive results.

But Yamasue has found signs of a much stronger link between the size of the ACC and the occurrence of post-traumatic stress. Many of those hurt in the Tokyo attack have shown symptoms of the disorder, ranging from nightmares and flashbacks to fear of riding trains.

Yamasue used an innovative magnetic resonance imaging technique that divides the brain into about a million small elements for computer analysis, enabling him to look at the whole brain at once. The results showed no correlation between the stress symptoms and the size of the hippocampal region. “We looked over the whole brain and only the ACC region was different,” he says.

A recent study of medical workers who served with the US army in Vietnam also suggested a correlation between the size of the ACC and post-traumatic stress (S. L. Rauch et al. NeuroReport 14, 913–916; 2003). But Roger Pitman, a Harvard psychiatrist and co-author of the study, believes that the size of the hippocampal region could correlate with post-traumatic stress in victims of “chronic, long-standing” trauma, including the subjects of most of the previous studies.

But researchers still don't know whether a smaller brain region is a result of the stress, or a pre-existing condition, perhaps genetic in origin, that made the subject more likely to display symptoms. Investigating possible links between hippocampal size and post-traumatic stress, Pitman has studied twins of whom one had experienced trauma (M. W. Gilbertson et al. Nature Neurosci. 5, 1242– 1247; 2002). His results tentatively suggest that the size factor may be a pre-existing condition but “the jury is still out on this”, he says.

Linking post-traumatic stress with specific areas of the brain could eventually aid the treatment of its victims. “If we understand the changes in brain structure and function we can develop better treatments targeted at specific brain pathways,” says Gerardo Villarreal, a psychiatrist at the University of New Mexico.