NPY and post-traumatic stress disorder: Individual variability in the reaction to a traumatic event leading to PTSD-like behavior was also shown to correlate with NPY levels in the amygdala and periaqueductal gray, i.e., exposed animals showed lower NPY levels than non-exposed and those classified as affected, i.e., exhibiting the greatest behavioral changes, showed lower levels than non-affected animals (Cohen et al., 2012).