Time-scale-invariant information-theoretic contingencies in discrimination learning

Animals optimize their behavior to maximize rewards by utilizing cues from the environment. In discrimination learning, cues signal when rewards can and cannot be earned by making a particular response. In our experiment, we trained male mice to press a lever to receive a reward on a random interval schedule. We then introduced a prolonged tone (20, 40, or 80 sec), during which no rewards could be earned. We sought to test our hypothesis that the duration of the tone and frequency of reward during the inter-tone-intervals affect the informativeness of cues and led to differences in discriminative behavior. Learning was expressed as an increase in lever pressing during the ITI and, when the informativeness of the cue was high, animals also reduced their lever pressing during the tone. Additionally, we found that the depth of discriminative learning was linearly related to the informativeness of the cues. Our results show that the time-scale invariant information-theoretic definition of contingency applied to excitatory conditioning can also be applied to inhibitory conditioning.

动物会借助环境中的线索（cue）优化自身行为，以最大化收益。在辨别学习（discrimination learning）范式中，线索会通过提示特定反应的方式，告知小鼠何时可获得收益、何时无法获得收益。本实验中，我们训练雄性小鼠通过按压操纵杆（lever）以随机间隔强化程序（random interval schedule）获取奖励。随后我们引入了时长为20、40或80秒的持续音（prolonged tone），该时段内无法获得奖励。我们旨在验证下述假说：持续音的时长以及音间间隔（inter-tone-intervals）内的奖励频率，会影响线索的信息量，并进而导致辨别行为产生差异。学习行为表现为：在音间间隔（inter-tone interval，缩写ITI）内小鼠按压操纵杆的频次增加；而当线索的信息量较高时，动物在持续音时段内的按压频次也会减少。此外，我们还发现辨别学习的深度与线索的信息量呈线性相关。本研究结果表明，适用于兴奋性条件反射（excitatory conditioning）的、具有时间尺度不变性（time-scale invariant）的信息论相依性（contingency）定义，同样可应用于抑制性条件反射（inhibitory conditioning）。