Once, there was a finding in research in 1997 by Verdoux et al., that, infants born from January to March in urban but not in rural area have been found to have higher risk of developing any type of schizophrenia. One possible cause is the seasonal effect might be the increasing prevalence of influenza & other viral disease during winter and spring. Some studies had found that if the mother had influenza while pregnant, child born of that pregnancy had an increased risk of schizophrenia. One test of this hypothesis was made possible by an unusually severe & time limited epidemic influenza in Helsinki Finland in 1957.
In some, but not all studies, individuals diagnosed with schizophrenia in adulthood have also been found to be more likely to have had obstetric complications at birth. In second trimester of pregnancy, brain cells migrate from their original position into more distant locations, where they establish connections with other neurons. This made researchers wonder if the brains of patients who had been diagnosed with schizophrenia would show a different organization of cells from what is generally expected. Even with the existence of sophisticated methods of neuroimaging, the primary way to answer this question is still by examination of brain tissues at autopsy.
Several studies of brain tissues have shown displacement of neurons in the brains of patients who had been diagnosed with schizophrenia. In each case, researchers found that, compared with controlled patients, the distribution of neurons was different. More cells were in the deeper layers of cortex & fewer towards the surface (Akbarian et al,. 1996). Because the cortex develop from inside towards outside, this finding suggests that many neurons failed to migrate as far as they should have. This in turn could disrupt the process of synaptic pruning. It's a developmental process in which neurons selectively reduce the number of branches of their dendrites. If it occurs abnormally, it can result in either too many or too few synapses, & consequent problem in cognitive function, an important difficulty in schizophrenia. In addition to developmental abnormalities in brain, development of the neuromotor system also seems to be affected in schizophrenia.