Eyeblink conditional discrimination learning in healthy young men is impaired after stress exposure.

Stress is known to influence the hippocampus. Eyeblink conditional discrimination learning is dependent on the hippocampus, but the effects of stress on the task are unknown. Male participants were allocated to a psychosocial stress condition (Trier Social Stress Test) or a control condition. Afterwards, a conditional discrimination task was performed. A tone (the CS) predicted an airpuff (the US) only when preceded by a specific visual stimulus (a red or a green colored square, the S+ and S-). Stressed participants showed a rise in cortisol and an increase in negative affect. Stressed participants also failed to acquire the conditional discrimination. They responded to all of the presented CS irrespective of the preceding occasion setter (S+ or S-). Controls, in contrast, acquired the discrimination rapidly. The present study provides further evidence for an impairing effect of acute stress on tasks relying on the hippocampal formation.