PMC

For both the individual familiarity and the strain familiarity experiments, the scatter plots indicate the prop. of time spent freezing by the demonstrator (x-axis) and observer (y-axis) during both baseline (black dots) and the shock period (red pluses). The marginal histograms indicate the distribution of freezing behavior during baseline (black lines) and the shock period (red lines) using a kernel with 0.05 bandwidth. Red arrow: possible influence of the demonstrator freezing on the observer freezing (akin to emotional contagion). Green arrow: possible influence of the observer freezing on the demonstrator freezing (akin to social buffering if the level of the observer freezing is lower than that of the demonstrator). Data can be found at http://dx.doi.org/10.17632/h8fkyr2z35.1. prop., proportion.

Probe CS after immediate extinction. (A) Percentage of freezing behavior during conditioning. Data are 1-min averages for the periods before (baseline, BL) and after each of five tone-shock conditioning trials. (B) Percentage of freezing behavior during the extinction session, which occurred 15 min after conditioning. Control rats did not receive CS presentations during extinction (NO-EXT). (C) Percentage of freezing behavior during the probe CS 15 min after extinction. Baseline freezing data were averaged and subtracted from the freezing level during probe CS to yield normalized freezing. (D) Normalized average percentage of freezing across test trials during retention test 48 h after conditioning. All data are means ± SEM.

Effects of intrahippocampal infusions of SAL, SCOP, and PHY on cue tone and contextual fear conditioning as a function of the conditioning procedure. A, Auditory cue test. Conditioned response to the tone is expressed as percentage of freezing increase to the tone with respect to a baseline freezing level (i.e., pre-tone/post-tone periods mean). The ratio was calculated as follows: [% freezing during the tone presentation − (% pre-tone period freezing + % post-tone period freezing)/2]/[% freezing during the tone presentation + (% pre-tone period freezing + % post-tone period freezing)/2]. Values of this ratio (mean ± SEM) are illustrated for mice submitted to SAL (n = 21), SCOP (n = 19), or PHY (n = 19) intrahippocampal infusions before either a CS–US pairing or a CS–US unpairing procedure. B, Context test. Percentage of conditioned freezing (mean ± SEM) during the 4 min reexposure period in animals submitted to SAL, SCOP, or PHY intrahippocampal infusions before either a CS–US pairing or unpairing procedure. C, Scopolamine dose effect on conditioned freezing to the tone CS (mean ± SEM) in mice submitted to SAL (n = 7) or SCOP intrahippocampal infusions [20 (n = 8), 50 (n = 17), or 100 μg/μl (n = 8)] before a CS–US unpairing procedure. D, Scopolamine dose effect on conditioned freezing to the context (mean ± SEM) in animals submitted to SAL or SCOP intrahippocampal infusions (20, 50, or 100 μg/μl) before a CS–US unpairing procedure. E, Physostigmine dose effect on conditioned freezing to the tone CS (mean ± SEM) in mice submitted to SAL (n = 14) or PHY intrahippocampal infusions [0.02 (n = 9), 0.1 (n = 9), or 1 μg/μl (n = 8)] before a CS–US pairing procedure. F, Physostigmine dose effect on conditioned freezing to the context (mean ± SEM) in animals submitted to SAL or PHY intrahippocampal infusions (0.02, 0.1, or 1 μg/μl) before a CS–US pairing procedure. * indicates conditioning effect (CS–US pairing vs unpairing); # indicates pharmacological effect (SAL vs SCOP or SAL vs PHY).

(a) Experimental protocol. (b) Behavioural results. During habituation (Hab.), mice (n = 13) exhibited low freezing during CS⁻ and CS⁺. Following conditioning (Day 2: Retrieval), CS⁺ (CS⁺ 1-12 grouped in blocks of 4) induced high freezing in comparison to CS⁻ (Paired t-tests, CS⁻ versus each CS⁺ block: t(12) = −11.929; t(12) = −11.929; t(12) = −8.442, *** all Ps < 0.001). (c) Percentage of freezing exhibited during and between CS⁺ presentations (Paired t-test, freezing inside versus between CS⁺: t(12) = −2.480, * P = 0.029). (d) Distribution probability for freezing episode duration as a function of whether freezing was initiated inside or between CS⁺ presentations. Inset: Percentage of freezing episodes initiated inside or between CS⁺ presentations (n = 13 mice, Paired t-test, t(12) = 2.762, * P = 0.016). (e) Cross-correlation analysis performed between freezing and CS⁺ onset (n = 13 mice, 100 ms bins). Red vertical dotted line represents freezing onset. Black horizontal dotted line represents significance level. Black arrow indicates the highest probability for CS⁺ onset at 1.5 s prior freezing onset. Error bars: mean ± s.e.m. For box plots, the middle, bottom and top lines correspond to the median, lower quartile and upper quartile and whiskers to lower and upper extremes minus lower quartile and upper quartile, respectively..