Fearlessness is a trait of psychopaths. It appears that the amygdala is dysfunctional in psychopaths :
" the amygdala is crucial for stimulus–reinforcement learning and responding to emotional expressions, particularly fearful expressions that, as reinforcers, are important initiators of stimulus–reinforcement learning. Moreover, the amygdala is involved in the formation of both stimulus–punishment and stimulus–reward associations. Individuals with psychopathy show impairment in stimulus–reinforcement learning (whether punishment or reward based) and responding to fearful and sad expressions. It is argued that this impairment drives much of the syndrome of psychopathy. Stimulus–reinforcement learning is crucial for socialization, for learning that some things are bad to do, and individuals with psychopathy fail to take advantage of standard socialization techniques."
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Fearlessness is a trait of psychopaths. It appears that the amygdala is dysfunctional in psychopaths :
" the amygdala is crucial for stimulus–reinforcement learning and responding to emotional expressions, particularly fearful expressions that, as reinforcers, are important initiators of stimulus–reinforcement learning. Moreover, the amygdala is involved in the formation of both stimulus–punishment and stimulus–reward associations. Individuals with psychopathy show impairment in stimulus–reinforcement learning (whether punishment or reward based) and responding to fearful and sad expressions. It is argued that this impairment drives much of the syndrome of psychopathy. Stimulus–reinforcement learning is crucial for socialization, for learning that some things are bad to do, and individuals with psychopathy fail to take advantage of standard socialization techniques."
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2606709/?tool=pm...