Using the magnetic resonance technique to study aspects of the limbic system (hippocampus) in 22 pairs of twins in which only one had diagnosed schizophrenia, they found that the mentally ill twin had smaller hippocampus. There was a significant correlation between labor complications and brain shrinking. Prolonged labor was one central culprit. The authors write, "Trauma at the time of labor and delivery and especially prolonged labor appear to be of importance for brain structure anomalies associated with schizophrenia." (Reuters. 2/22/2000)
What the authors contend, something I have described for decades, is that the birth trauma has something to do with later mental illness. Further, that the feeling system is grossly affected by this trauma. This means that birth trauma affects all manner of feeling states later on, whether of suicidal tendencies or criminal proclivities. So the central questions: "Why does one twin become mentally ill and not the other?", can be partially answered by reference to the birth trauma. Not only the birth trauma, but most importantly, what happened in the womb. We must consider the background, historical effects that made the neonate vulnerable to the birth trauma.