T cells, probably by influencing microglia, are vital to the brain’s repair after stroke, for precluding a reduction in levels of BDNF following a psychological stressor, for avoiding symptoms of post traumatic stress disorder (PTSD) after psychological stress, for spatial learning, for neurogenesis stimulated by exercise (Cohen et al., 2006; Ziv et al., 2006; Ziv and Schwartz, 2008a,b; Schwartz and Shechter, 2010a) and for capacity to detoxify reactive alpha-oxoaldehydes (Ron-Harel et al., 2011). This evidence concerns the gene BDNF and post-traumatic stress disorder.