Relationship of the 'fear-inhibited light reflex' to the level of state/trait anxiety in healthy subjects.

RATIONALE It has been shown that the amplitude of the pupillary light reflex response decreases when subjects anticipate an aversive stimulus (i.e. electric shock), compared to periods when subjects are resting ('fear-inhibited light reflex'). OBJECTIVE To examine whether the sensitivity of the pupillary light reflex to the threat of an electric shock is related to the pre-existing levels of state and trait anxiety. METHODS Thirty-two healthy volunteers participated in one experimental session. The possibility of an electric shock to the wrist was signalled by a tone. There were six blocks of three light stimuli: three SAFE blocks (no tone applied) and three THREAT blocks (tone applied). The State-Trait Anxiety Inventory was completed at the beginning and at the end of each session. RESULTS There was a positive correlation between the state anxiety scores and the within-subject (SAFE-THREAT) difference in light reflex amplitude (P<0.05). There was no significant correlation between the trait anxiety scores and the within-subject differences in light reflex amplitude. CONCLUSIONS Individual differences in state anxiety associated with the threat of an electric shock are reflected in the amplitude of the pupillary light reflex response. This observation strengthens the validity of the fear-inhibited light reflex as a model of human anxiety.