One possible explanation of this negative finding is the possibility of high developmental plasticity of the neural organization of emotional reactivity which allows the organism to adapt flexibly to the changing environment. However, there is another, more parsimonious explanation: test-retest assessments suggest very low individual stability of emotion-modulated startle (Larson et al., 2005; Lee et al., 2009), which casts doubt on the notion that it can serve as an indicator of stable, trait-like individual differences. However, these negative findings do not preclude the possibility that individual differences in emotion-modulated startle are influenced by genetic factors. First, the study by Anokhin et al. (2007a) included only females, and there is a possibility that emotion-modulated startle is heritable in males but not females. Second, measures of startle modulation in other experimental paradigms may be under greater genetic influences. For example, twin studies of startle modulation by affective facial expressions or fear-potentiated startle can help to clarify this issue.
