Effects of anxiety sensitivity and expectations on the modulation of the startle eyeblink response during a caffeine challenge.

RATIONALE: The way in which the tendency to fear somatic arousal sensations (anxiety sensitivity), in interaction with the created expectations regarding arousal induction, might affect defensive responding to a symptom provocation challenge is not yet understood.
OBJECTIVES: The present study investigated the effect of anxiety sensitivity on autonomic arousal, startle eyeblink responses, and reported arousal and alertness to expected vs. unexpected caffeine consumption.
METHODS: To create a match/mismatch of expected and experienced arousal, high and low anxiety sensitive participants received caffeine vs. no drug either mixed in coffee (expectation of arousal induction) or in bitter lemon soda (no expectation of arousal induction) on four separate occasions. Autonomic arousal (heart rate, skin conductance level), respiration (end-tidal CO2, minute ventilation), defensive reflex responses (startle eyeblink), and reported arousal and alertness were recorded prior to, immediately and 30 min after beverage ingestion.
RESULTS: Caffeine increased ventilation, autonomic arousal, and startle response magnitudes. Both groups showed comparable levels of autonomic and respiratory responses. The startle eyeblink responses were decreased when caffeine-induced arousal occurred unexpectedly, e.g., after administering caffeine in bitter lemon. This effect was more accentuated in high anxiety sensitive persons. Moreover, in high anxiety sensitive persons, the expectation of arousal (coffee consumption) led to higher subjective alertness when administering caffeine and increased arousal even if no drug was consumed.
CONCLUSIONS: Unexpected symptom provocation leads to increased attention allocation toward feared arousal sensations in high anxiety sensitive persons. This finding broadens our understanding of modulatory mechanisms in defensive responding to bodily symptoms.