FEAR-POTENTIATED STARTLE CONDITIONING IN HUMANS - EXPLICIT AND CONTEXTUAL CUE CONDITIONING FOLLOWING PAIRED VERSUS UNPAIRED TRAINING

Conditioned fear in response to explicit and contextual cues was exami ned using the startle reflex in three groups of participants over two sessions separated by 4-5 days. The conditioned stimulus (CS) was pair ed with an aversive unconditioned stimulus (US) (shock) during conditi oning in the paired but not in the unpaired group. In the reaction tim e (RT) group, the US was a nonaversive visual signal for an RT task. I n the paired group, the CS potentiated startle in the postconditioning phase. This conditioned response was fully retained over the retentio n interval. There was no substantial change in baseline startle (start le delivered in the absence of CS). By contrast, startle was not poten tiated by the CS in the unpaired group, but baseline startle was incre ased from Session 1 to Session 2. In the RT group, startle was not aff ected by the CS, and baseline startle was reduced from Session 1 to Se ssion 2. These results suggest that paired presentations of a CS and a n aversive US result in conditioned fear in response to the CS but lit tle contextual fear, whereas unpaired presentations of a CS and US lea ds to poor explicit cue conditioning but substantial contextual fear.