Many Brain Regions More than a dozen brain areas are more reactive to stress when a person has only the short allele of 5-HTTLPR. That is shown in these brain scans from a study of healthy college women who were paid to undergo an experiment involving 12 episodes without shocks, 13 with moderate shocks, and 13 with stronger (painful but not extreme) shocks. Uncertainty increased stress: The women did not know exactly when or how strong the shocks would be. People with only the short version of 5-HTTLPR were much more anxious overall, with more areas of their brains activated (shown here in red), compared with those who had the long version.