A twin study using the PPI paradigm has shown high heritability of the overall startle response magnitude (68%) and slightly lower heritability (58%) of the PPI index (Anokhin et al., 2003). Importantly, a separate analysis of the first and the second half of the experiment showed attenuation of heritability, which can be explained by overall startle habituation in the course of the experiment leading to the “floor effect” in the assessment of startle amplitude. Thus, contrary to the more common case when larger number of trials usually leads to more reliable estimate of the response, in the case of PPI a shorter experiment can yield more heritable measures.
