The Relationship of Defensive Behavior with Cognitive Bias in Mice

Mendonca, Alex, Victoria Caputo, Daniel Jones, and Elizabeth Hill

There has recently been research interest in the phenomenon called judgment bias or cognitive bias in laboratory rodents because of its application to animal welfare and models of human depression (Harding, Paul & Mendel, 2004). In the cognitive bias paradigm, animals are trained to associate different signals to reinforcement or aversion.  Then, an ambiguous signal is presented.  Their response shows a positive (“optimistic”) or negative (“pessimistic”) orientation or bias.  However, it is not clear how much of the behavior in the ambiguous presentation trial could be due to more general behavior patterns such as level of exploratory behavior, defensiveness, or risk aversion.  The present study was designed to examine the relationship of measures from cognitive bias tests with measures of defensive and exploratory behavior.  The hypothesis was that higher defensive behavior would correlate negatively with indicators of “optimism” in the cognitive bias test.  Thirty-five mice of the C57BL/6 strain were tested in a cognitive bias tests, with 31 also given open-field tests.  On sixteen cognitive bias tests, extensive observations were made of defensive behavior (Blanchard et al., 2001).  Cognitive bias tests entailed four discrimination training days followed by a fifth day testing with an ambiguous stimulus.  The latency to approach the reward (an almond) indicates degree of optimism.  Open-field tests were conducted in a standard-sized aquarium with an open floor area and a plastic shelter.  Throughout the cognitive bias tests, defensive behaviors were recorded including: approach and retreat, digging, number of pellets, and stretched attend. The results were that the ambiguous test latency to grab the almond was not significantly correlated with other testing measures.  However, most mice were very quick on the ambiguous trail, resulting in a restricted range for a correlation.  There was more range on the grab latency for the last negative trial (e.g., Last negative grab with digging during negative trials, r= .310, n.s.; with digging during positive trials, r= .451, p=.092, n=15).  The defensive behaviors were significantly correlated with responses in the open field test.  There was a strong positive correlation between the amount of digging during negative cognitive bias trials and the time spent  in the shelter in the open field tests (r=.614, p=.011).  Digging frequency also correlated with the latency to leave the shelter to investigate a novel odor.  The results suggest that defensive behavior in the two tests was related.  Defensive behavior may indicate more risk aversion.  In this study only a small sample of mice had both measures.  Future research with a larger sample size relating defensive behavior and cognitive bias tests is suggested as the next step in understanding whether performance in the ambiguous trails indicates “optimism.”