Contextual fear induced by unpredictability in a human fear conditioning preparation is related to the chronic expectation of a threatening US

The present study was set up to investigate cued and contextual fear in situations of (un)predictability in a human fear conditioning paradigm. Forty-nine participants were presented with two different contexts (switching on and off the central lighting of the experimental room). In the predictable context, a visual cue (CS I) was systematically followed by an electrocutaneous stimulus (US). In the unpredictable context, CS2 was presented explicitly unpaired with the US. Dependent variables were online US-expectancy ratings and fear-potentiated startle. First, in both measures, the results showed significantly more fear elicited by CS I than by CS2. Second, larger startle amplitudes during the intertrial intervals demonstrated more contextual fear in the unpredictable than in the predictable context. Hence, these findings illustrate that unpredictability increases contextual fear. Moreover, the US-expectancy ratings during the intertrial intervals were also higher in the unpredictable than in the predictable context. This last finding suggests that a chronic expectation of the threatening US is responsible for sustained levels of anxiety in unpredictable situations. (C) 2007 Elsevier B.V. All rights reserved.