Data about each animal (sex, date of birth, lineage), their water intake and weights were logged in the Alyx colony management system (The International Brain Laboratory et al., 2019) and analyzed using DataJoint (Yatsenko et al., 2018). We visualized all data in python, using pandas and seaborn (Waskom et al., 2020). Statistics were done using the Pingouin package (Vallat, 2018).

For psychometric function parameters, as well as learning rates, daily trial counts and trial durations, we report statistics from an independent t test to test the effect of weekend water regime (Fig. 3). The degrees of freedom were corrected for unequal variances using a Welch–Satterthwaite correction. The corresponding Bayes factor indicates evidence for the null hypothesis of no difference when <1.

Weekend CA water does not adversely affect learning behavior. A, Weight curves (normalized by each animal’s free water weight), separately for animals receiving measured water (in accordance with local IACUC protocols) or free 2% CA water on weekends and other non-training days. B, Trial counts in a decision-making task over the course of learning. Training started ∼8 d after the beginning of water restriction. C, Learning curves, showing performance on easy trials with 50% or 100% visual contrast. DI, Various measures of learning rates and stable behavior, separated by the weekend regime used in each lab. D, Number of days until reaching training criteria. EI, For the three days over which animals passes training criteria, (E) average number of trials performed per day, (F) threshold from a psychometric function fit, (G) choice bias from a psychometric function fit, (H) lapse rate from a psychometric function fit, and (I) median trial duration. See Extended Data Figure 3-1 for an examination of sex differences.

Sex differences. We tested whether the weekend water regime (2% CA bottle vs measured water) differently affected (A) female and (B) male mice. Female mice given measured water on weekends learned the task slightly slower than female mice given 2% CA on weekends (t(27) = –2.89, p = 0.007, Bf10 = 7.731). This was not the case for male mice (t(77) = 0.30, p = 0.762, Bf10 = 0.242). Learning speeds showed a main effect of sex, and a significant interaction between water regime and sex (two-way ANOVA: effect of sex F(1) = 14.367, p < 0.001; effect of water regime F(1) = 4.645, p = 0.033; interaction F(1) = 9.457, p = 0.003). The overall slower learning speeds of female mice may be due to their lower weights, causing them to be satiated more quickly and performing fewer trials early in the training process (we gave all animals a fixed reward volume, independent of their body weight). We can speculate that animals’ weight and hydration balance may be slightly different in different water regimes, which interacts with motivation and learning speed in a sex-specific manner. Learning speeds differ between labs, which may be caused by various factors (The International Brain Laboratory et al., 2020). Further work is thus needed disentangle any sex differences in the effects of water regime on task learning. There was no significant effect of sex, or interaction between sex and water regime, for stable behavior upon training completion: daily trial counts (effect of sex F(1) = 0.345, p = 0.558; effect of water regime F(1) = 2.070, p = 0.153; interaction F(1) = 0.061, p = 0.806), visual threshold (effect of sex F(1) = 0.142, p = 0.707; effect of water regime F(1) = 0.002, p = 0.962; interaction F(1) = 0.584, p = 0.446), choice bias (effect of sex F(1) = 0.825, p = 0.365; effect of water regime F(1) = 1.374, p = 0.243; interaction F(1) = 0.027, p = 0.869), lapse rate (effect of sex F(1) = 2.085, p = 0.151; effect of water regime F(1) = 2.284, p = 0.133; interaction F(1) = 0.320, p = 0.573), or trial duration (effect of sex F(1) = 2.730, p = 0.101; effect of water regime F(1) = 0.064, p = 0.801; interaction F(1) = 2.457, p = 0.119). Download Figure 3-1, TIF file.

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