BDNF and post-traumatic stress disorder: While it might seem counterintuitive to suggest that individuals carrying the BDNF Met allele would have reduced recollection of emotional stimuli, as this genotype is associated with post-traumatic stress disorder (PTSD), it is not without precedent; an fMRI study of PTSD flashbacks has shown that neurally the are more similar to a strong sense of familiarity than to recollection (Whalley et al., 2013).