Startle potentiation: shock sensitization, aversive learning, and affective picture modulation.

This study investigated the size of, and relationship between, different modulatory effects of aversive stimulation on the acoustic startle reflex. This reflex is potentiated by shock exposure and associative shock conditioning (in animals and human volunteers) and unpleasant pictures (in human volunteers). In this study, dramatic sensitization of the probe-startle response was observed after shock exposure but not after a control task. Magnitude of sensitization was significantly larger than associative shock conditioning and picture modulation effects (also significant). Sensitization and conditioning scores showed modest, significant correlations with one another but not with picture modulation scores, consistent with animal data showing that partially overlapping brain mechanisms (i.e., amygdaloid-reticular projections) mediate these effects. The present results also indicate that sensitization of startle in human volunteers is a relatively more robust defensive response to aversive stimulation.