Incubation of fear

Abstract

While fear and anxiety can grow over time in anxiety disorders, most efforts to model this phenomenon with fear conditioning in rodents cause fear that remains stable or decreases across weeks or months. Here, we describe several methods to induce conditioned fear that grows over the course of 1 month and is sustained for at least 2 months using an extended fear conditioning approach. These methods include a very reliable standard method that causes multiple fear measures to increase over months, as well as alternative methods.

Figure 1

Time-line for Basic Protocol 1 and Alternate Protocol 1.

Figure 2

Time-course of fear incubation using the procedure described in Basic Protocol 1. The measure of fear is conditioned suppression of lever-pressing (mean+SEM). * significantly different from day 2 (p < 0.05). Adapted, with permission, from (Pickens et al., 2009b).

Figure 3

Comparison of fear expression after limited (1 day) or extended (10 day) training. A: Fear expression after training with 30-sec cues (as in Basic Protocol 1). B: Fear expression after training with 6-min cues (as in Alternate Protocol 1). The measure of fear is conditioned suppression of lever-pressing (mean+SEM). * significantly different from day 2 (p < 0.05). Adapted, with permission, from (Pickens et al., 2009b) and (Pickens et al., 2010).

Figure 4

Different trial-by-trial patterns of fear incubation (idealized data). A: Higher fear expression on day 31 on every trial during the fear test. B: Higher fear expression on day 31 early in the test with the differences disappearing on later trials. C: Similar early in the test due to ceiling effects, with fear expression on day 31 higher on later trials.