DOI: 10.5061/dryad.2bvq83bsd
title: Once an optimist, always an optimist? Studying cognitive judgment bias in mice

description: This repository contains raw data and analysis code for the manuscript
 entitled "Once an Optimist, Always an Optimist? Studying Cognitive
 Judgment Bias in Mice" from Marko Bračić, Lena Bohn, Viktoria
 Siewert, Vanessa von Kortzfleisch, Holger Schielzeth, Sylvia Kaiser,
 Norbert Sachser, S. Helene Richter, accepted for publication in the
 journal Behavioral Ecology. The aim of the study was to investigate the
 causes and stability of cognitive judgment bias (aka
 "optimism"). Individuals differ in the way they judge ambiguous
 information: some individuals interpret ambiguous information in a more
 optimistic, and others in a more pessimistic way. Over the past two
 decades, such “optimistic” and “pessimistic” cognitive judgement biases
 (CJBs) have been utilized in animal welfare science as indicators of
 animals’ emotional states. However, empirical studies on their ecological
 and evolutionary relevance are still lacking. We, therefore, aimed at
 transferring the concept of “optimism” and “pessimism” to behavioral
 ecology and investigated the role of genetic and environmental factors in
 modulating CJB in mice, using an automated, touchscreen-based active
 choice paradigm. In addition, we assessed the temporal stability of
 individual differences in CJB. We show that the chosen genotypes (C57BL/6J
 and B6D2F1N) and environments (“scarce” and “complex”) did not have a
 statistically significant influence on the responses in the CJB test. By
 contrast, they influenced anxiety-like behavior (assessed in the elevated
 plus maze (EPM), an open field test (OFT), and a free exploration test
 (FET)) with C57BL/6J mice and mice from the “complex” environment
 displaying less anxiety-like behavior than B6D2F1N mice and mice from the
 “scarce” environment. As the selected genotypes and environments did not
 explain the existing differences in CJB, future studies might investigate
 the impact of other genotypes and environmental conditions on CJB, and
 additionally, elucidate the role of other potential causes like endocrine
 profiles and epigenetic modifications. Furthermore, we show that
 individual differences in CJB were repeatable over a period of seven
 weeks, suggesting that CJB represents a temporally stable trait in
 laboratory mice. Therefore, we encourage the further study of CJB within
 an animal personality framework.
description: The experiment lasted for one year (February
 2019 – March 2020) and was conducted in two independent
 <strong>batches</strong>. Laboratory mice were obtained from a
 professional breeder at the age of four weeks and housed at the University
 of Münster. We housed female mice of two
 strains/<strong>genotypes</strong> (C57BL/6J and B6D2F1N) in
 two <strong>environmental conditions</strong>: a “scarce
 environment” and a “complex environment”. Mice were housed in same-strain
 groups of three individuals per <strong>cage</strong>. To
 allow for individual identification within cages, all mice received
 partial ear punches (earcut) upon arrival. The three mice housed in the
 same cage were exposed to the same environmental conditions but
 participated in different sets of the following experimental phases: a
 touchscreen training phase (TS), first cognitive judgement bias (CJB) test
 phase, repeated CJB testing phase, and behavioral test phase.
 One mouse from each cage was touchscreen
 trained and tested in the first CJB test phase before it was removed from
 the cage to participate in another experiment. The second mouse was
 touchscreen trained as well but was then repeatedly tested in the CJB test
 (four CJB <strong>tests</strong> in total) and afterward
 entered the behavioral test phase. The third mouse in a cage participated
 only in the behavioral test phase. With the data from the three experimental phases,
 we created three different datasets contained in this repository, each
 with a different sample size:  
 <strong>CJB_genotype-environment.txt</strong> contains source
 data used to analyse the influences of genotype and environment on CJB
 (<strong>first cognitive judgement bias (CJB) test phase, N =
 39</strong>) 
 <strong>CJB_repeatablity.txt</strong> contains source data
 used to analyse the repeatability of CJB (<strong>repeated CJB
 testing phase, N = 19</strong>) <strong>behavioural_tests.txt</strong>
 contains source data used to analyse the influences of genotype and
 environment on anxiety-like behaviour and spatial learning
 (<strong>behavioral test phase, N = 36</strong>)
 Cognitive judgment bias (CJB) test The choice score obtained from the CJB test served
 as a relative behavioral indicator of CJB. The choice score was calculated
 based on the mice’s responses (optimistic or pessimistic) during 5 testing
 sessions (days) for each individual for each cue (positive, near positive,
 middle, and near negative, negative). Formula: Choice Score = (N choices
 ("optimistic") - N choices ("pessimistic")) / ( N
 choices ("optimistic" + "pessimistic"))
 Data were automatically recorded by the ABET
 II software (version 2.20., Campden Instruments Ltd., Loughborough,
 Leics., UK) and the choice score was calculated in R. As individuals needed different numbers of
 touchscreen training sessions before the CJB test, they were tested on
 different dates. The location of the correct side for the cues was
 counterbalanced between mice (trial_type): e.g., one mouse per cage had to
 touch the right-hand side in response to the positive cue to get a big
 reward, while the other mouse had to touch the left-hand side in response
 to the positive cue.  Behavioral
 tests The test battery included an
 elevated plus maze (EPM), an open field test (OFT), and a free exploration
 test (FET) to assess anxiety-like behavior and exploration. The subsequent
 labyrinth maze (LM) served to measure spatial learning. Tests were video
 recorded (Logitech Webcam Pro 9000) and automatically tracked (ANY-maze,
 version 5.33, Stoelting Co., Wood Dale, IL, USA). Data analysis Data were analysed by using linear mixed-effects
 models (LMM) in R (version 4.1.2) . Data analysis can be replicated with
 provided R scripts.
description: Variables in the dataset are explained in the ReadMe file and further clarified in the methods above (variables marked bold). Due to a setup error in the labyrinth maze (LM), three mice had to be excluded from the (labyrinth maze) analysis (NA). For the analysis of each dataset, a separate R script is provided. To successfully run the R script, make sure that the data files are in R working directory (e.g. keep data and script in the same folder or change the working directory to the folder where data is saved) and that listed R packages are installed.