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. 2018 Nov 23;236(1):33–48. doi: 10.1007/s00213-018-5111-5

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© The Author(s) 2018

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Fig. 2 — Variability in parametric settings of auditory stimuli affect fear conditioning experiments. a A literature survey on fear conditioning experiments in mice (> 350 studies performed between 2000 and 2010) revealed a broad variability in quality (frequency of sine-wave tones vs. white noise (wn)), duration and intensity of the conditioned stimuli (CS). b Direct comparison of consequences of white noise (wn) vs. sine wave (sw 9 kHz, 80 dB) stimuli on auditory fear conditioning and fear extinction. (1) Before conditioning, we compared the sensitivity of single-house male C57BL/6N mice (n = 11 per group) to startle pulses of different quality (white noise vs. sine wave) and intensity and observed in increased sensitivity to the sine wave tone as measured by acoustic startle responses (ASR; two-way rmANOVA, CS quality × SPL: F_4,80 = 7.163, p < 0.0001). On basis of these data we selected an intensity of 80 dB for the subsequent fear conditioning with a single CS (20 s) -shock (0.7 mA, 2 s) pairing using the delay protocol (cf. Fig. 1c) in context A. (2) The day after fear conditioning, we placed the animals into a novel context (B) and repeatedly exposed them to nine CS (20 s, variable interval 30–140 s) per day on three consecutive days (d1–d3). We assessed retention of fear extinction by presenting another 4 CS to the animals at day 9. Long-term extinction was analyzed on basis of the freezing responses shown during the first tone presentation per day (cf. Fig. 3b; CS quality × day: F_3,60 = 11.17, p < 0.0001), indicating the success of extinction training with sine wave but not with white noise stimuli. (3) This conclusion was substantiated, if freezing just before the first tone presentation (CS−) at day 9 was compared with freezing during the subsequent 20-s tone presentation (CS+), whereby the white noise, but not the sine wave stimulus still caused a sharp increase in freezing (CS quality × CS: F_1,22 = 30.69, p < 0.0001). (4) The situation was different, if animals were exposed to the CS in the conditioning context. Both groups showed the same level of contextual fear before CS presentation. This time, however, presentation of the white noise caused a decrease in freezing compared to the sine wave stimulus (CS quality × CS: F_1,22 = 4.968, p = 0.0364), likely because of an explosive outburst of active fear (Fadok et al. 2017)