Suggested U-shaped relationship between 5-HT levels and the extent of fear conditioning. Available studies suggest that both too high (e.g., 5-HTTLPR s-allele, 5-HTT knockout, MAO-L, acute SSRI) and too low (e.g., Lmx1b knockout, ATD, pCPA) 5-HT levels increase associative learning and strengthen the association between the CS and the shock.
