We are aware of only one study, not conducted in smokers, in which the effects of the 5-HTTLPR was studied specifically in relation to the human startle response. That study showed that 5-HTTLPR short allele carriers exhibited heightened startle responses compared to those with the l/l genotype (Brocke et al., 2006). However, the authors were unable to confirm their hypothesis that the s carriers would exhibit heightened fear-potentiated startle responses in comparison to those with the l/l genotype, as they found no interaction with picture content. Other studies have suggested that the manipulation of serotonin levels using pharmacological treatment may potentiate (Liechti, Geyer, Hell, & Vollenweider, 2001; Hayward, Goodwin, Cowen, & Harmer, 2005), attenuate (Murphy, Longhitano, Ayres, Cowen, & Harmer, 2006), or have no effect at all (Phillips, Langley, Bradshaw, & Szabadi, 2000; Quednow et al., 2004) on the startle response.
