E-Mail A post-mortem analysis of brain tissue from people who had been diagnosed with post-traumatic stress disorder (PTSD) may help explain enduring mysteries about the disorder, such as why women are more susceptible to it and whether a dampened immune system response plays a role in dealing with stress, a team headed by Yale University researchers has found. The analysis of gene expression patterns in brain tissue located in four regions of the prefrontal cortex -- areas of the brain associated with higher cognitive function and executive control -- revealed distinct differences in those who had been diagnosed with PTSD and those who had not. Major differences in gene activity particularly affected two cell types in PTSD patients -- interneurons, which inhibit neural activity, and microglia, immune system cells in the central nervous system, the researchers report Dec. 21 in the journal