Following previous research suggesting that the volume of the hippocampus was reduced in some people with chronic PTSD, a twin study indicated that this may not be simply a sign that stress has shrunk the hippocampus, but that those with a smaller hippocampus are at greater risk of PTSD. Now a new study has found that Gulf War veterans who recovered from PTSD had, on average, larger hippocampi than veterans who still suffer from PTSD. Those who recovered had hippocampi of similar size to control subjects who had never had PTSD.
The study involved 244 Gulf War veterans, of whom 82 had lifetime PTSD, 44 had current PTSD, and 38 had current depression.
Because we don’t know hippocampal size prior to trauma, the findings don’t help us decide whether hippocampal size is a cause or an effect (or perhaps it would be truer to say, don’t help us decide the relative importance of these factors, because it seems most plausible that both are significant).
The really important question, of course, is whether an effective approach to PTSD treatment would be to work on increasing hippocampal volume. Exercise and mental stimulation, for example, are known to increase the creation of new brain cells in the hippocampus. In this case, the main mediator is probably the negative effects of stress (which reduces neurogenesis). There is some evidence that antidepressant treatment might increase hippocampal volume in people with PTSD.
The other conclusion we can derive from these findings is that perhaps we should not simply think of building hippocampal volume / creating new brain cells as a means of building cognitive reserve, thus protecting us from cognitive decline and dementia. We should also think of it as a means of improving our emotional resilience and protecting us from the negative effects of stress and trauma.
 . Hippocampal Volume Differences in Gulf War Veterans with Current Versus Lifetime Posttraumatic Stress Disorder Symptoms. Biological Psychiatry [Internet]. 2011 ;69(6):541 - 548. Available from: http://www.sciencedirect.com/science/article/B6T4S-51HJBJW-3/2/58dcc7041f71853ebd88310dc8f865a1
 . Smaller hippocampal volume predicts pathologic vulnerability to psychological trauma. Nature neuroscience. 2002 ;5(11):1242 - 1247. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2819093/