Among the MAPK family genes, Ras-associated protein 1A (RAP1A/Rap1a) was strongly co-expressed with PDE4B (Supplementary Table 3) and significantly downregulated in relation to PTSD reexperiencing symptoms (Supplementary Table 2) and mouse fear memory retrieval (Fig. 6 and Supplementary Table 2). Here, PDE4B is linked to post-traumatic stress disorder.