Procedures and results of Experiment 1.

<p>(A) Schematic showing the timeline and illustration of the procedures conducted in <i>Experiment 1</i>. Following acclimation to the colony room and 7 days of handling, <i>Observer-Demonstrator</i> pairs were habituated to the test box (20 minutes/day for 3 days). One day prior to the first empathy test, <i>Observers</i> experienced mild shock exposure. Then, <i>Observer-Demonstrator</i> pairs experienced 6 semi-consecutive footshock sessions with only 2 days of no test between empathy test 4 and 5. (B) Graph of the freezing responses of <i>Observers</i> (gray line) and <i>Demonstrators</i> (black line) and yawning of <i>Observers</i> (red line). The figure depicts average freezing percent ± standard error of the mean (SEM) of 6 test days (1 to 6) each consisting of a baseline (2 minutes prior to 1^st shock) and 5 shock periods: 1^st to 2^nd shock, 2^nd to 3^rd shock, 3^rd to 4^th shock, 4^th to 5^th shock and 5^th plus 2 additional minutes, corresponding to numbers 1 to 5 in the graph. For each test day, freezing percent was compared between time periods where shocks were delivered (i.e., time periods 2, 3, 4, 5 and 6) and baseline period. Black significance symbols are for <i>Demonstrators</i> while grey-colored symbols are for <i>Observers</i>. In addition, graph shows the cumulative (i.e., daily) median yawning of <i>Observers</i> for test days 1 to 6 (red colored y axis on the right side). (C) Top left graph shows the total number of yawns displayed by <i>Observers</i>. Comparisons were made between the numbers of normalized yawns during shock period of test days 2 to 6 (normalized to preshock) and normalized yawns during test day 1. Top right graph shows the percent of <i>Observers</i> that yawned at least once and the cumulative percent across test days of <i>Observers</i> that yawn (pink bars). Bottom left graph shows the total number of yawns over all <i>Observers</i> during the shock period (minus the yawns during the preshock period) in the control condition (i.e., no pretreatment with metyrapone) and following a subcutaneous injection of metyrapone (25mg/kg) prior to test. Bottom right graph shows the mean percent of time <i>Observers</i> spent in the window zone (i.e., area closest to the separation from the <i>Demonstrators-</i>bottom panel). All graphs show results during the preshock (gray) and shock (black) periods of test days 1 to 6. Numbers on top of the bars indicate the range of yawns displayed by the animals. ***p<0.005, **<i>p</i><0.01, *<i>p</i><0.05, <i>t</i>:<i>p</i> = 0.072.