Figure 2.

Fiber placement and experimental design. A, Fiber placements for rats in each of the four groups: ArchT unsilenced controls (ArchT-control; n = 8), ArchT Trial-silenced (Trial-silenced; n = 7), inactive virus control (GFP-control; n = 8), and ArchT UCS-silenced (UCS-silenced; n = 4). Shaded bars in stimulus diagrams represent timing of laser delivery during paired trials for each group. B, Procedural timeline of training and testing following virus injection. Preexposure consisted of 2 nonreinforced 30 s presentations of a 6 kHz tone and white noise CS. Training consisted of 2 pairings of a 10 s CS with a 1 s footshock UCS (0.6 mA) separated by a 20 s trace interval each day for 3 d. A CS test in a shifted context was administered before training on days 2 and 3. On day 4, a CS test was followed by a CT, with no further training. Each CS test consisted of two 30 s tones and four 30 s CSs. All rats received the same training and testing protocol with one exception: only the ArchT-control and Trial-silenced active virus groups received two additional CTs 12 d later, with or without laser delivery to assess VH-PL silencing on the expression of fear (Expression Tests; see Figure 6). Coronal diagrams were adapted from (Paxinos and Watson, 2007) with permission.