Induced Positive Affect Reduces the Magnitude of the Startle Response and Prepulse Inhibition

The startle response is a reflex that represents a form of adaptation to environmental changes potentially relevant to survival. Startle magnitude can change depending on a number of factors such as the affective state of the organism during the presentation of the startle-inducing stimulus, or the so-called Prepulse Inhibition (PPI) that occurs when the startling stimulus (or Pulse) is preceded by a low-intensity stimulus (or Prepulse). This paper describes an experiment designed to analyze the impact of an induced positive affect on the magnitude of the startle response and PPI in adult humans. Specifically, each participant received alternating exposures to a picture of a face of a loved person (positive affect condition) or to a picture of a face of an unknown person (control condition) while the startle response and PPI were recorded. The results showed a decrease in both the magnitude of the startle response and percent PPI on the positive affect trials when compared with the control trials. These results are interpreted from psychophysiological and psychological perspectives considering the role of emotions in adaptive behavior.