Activated Tryptophan-Kynurenine metabolic system in the human brain is associated with learned fear

Abstract

Fear is widely recognized as a defensive emotion that has developed as a consequence
\nof its adaptive function in protecting the entire animal kingdom from danger, ensuring
\nthe survival (Bouton, 2002; Milad and Quirk, 2002). Although fear associated with specific
\nstimuli is an innate emotion (e.g., a loud noise triggering fear in infants, fear of potential
\npredators), it can also be acquired rapidly and permanently to enable an appropriate and
\nadaptive response to new or unpredictable environmental situations (LeDoux, 2000; Beckers
\net al., 2013).