With free access to food and water, mice were indifferent to risk.

<p>A. Experienced risk measured by reward variance. The actual experienced risk is calculated by counting the safe reward size (0.01 ml) as 1. When the trial is unrewarded, the outcome is 0, when the outcome is 0.02 ml or twice the safe reward size, the outcome is counted as 2. Error bars indicate standard error of the means (SEM). Sucrose = 10% sucrose; alcohol = 10% sucrose and 20% ethanol. B. Risk preference under different levels of risk (average of last 3 sessions; probability of reward on the risky lever = 12.5%). Mice were trained successively on 4 levels of risk (100%, 0.01 ml; 50%, 0.02 ml; 25%, 0.04 ml; 12.5%, 0.08 ml). Risk aversion index was calculated by dividing number of safe choices by the total number of presses. If the index is greater than 0.5, the animal is risk averse; if it is less than 0.5, the animal is risk prone. C. Number of presses on the two levers (average of last 3 sessions; probability of reward on the risky lever = 12.5%). D. Rate of lever pressing during the last session.