EN
INTRODUCTION: Natural rewards and addictive substances both act on the brain’s reward system, however it remains unclear whether they reinforce actions through the same mechanisms. AIM(S): Our goal was to compare the strategy employed by mice when choosing between two actions with variable chance to access alcohol or sweetened solution. METHOD(S): We have developed a novel method to assess behavioral strategy employed by mice when selecting between options associated with different probabilities of receiving a reward. A group of animals is implanted with radiofrequency chips and introduced to an IntelliCage, where their activity in cage corners is continuously recorded. After a period of adaptation, mice are offered accessto saccharin or alcohol solution in two opposite corners, with free access to water in the remaining corners. Initially, upon entering a rewarded cornerthere is a 90%chance that accessto saccharine or alcohol solution will be granted after 2 seconds. As the procedure progresses, the probability changes periodically between 90% and 30% and cycles through all possible combinations between the two rewarded corners. RESULTS: We tested choice between solutions 0.1% (w/v) saccharin, 4% (v/v) ethanol or a combination of them. In case of the sweetened water reward, the main factor affecting choice was time elapsed from last decision. The effect of the outcome of the previous choice was also significant, but overall smaller. In case of the alcohol solution, the effects of time and previous outcome were weaker, animals were more likely to repeat previous choice. We also observed that irrespective of strategy choices follow a specific time pattern, with majority occurring at discrete intervals. CONCLUSIONS: The type of reward strongly affected animals’ behavioral strategy. Probabilistic access to sweetened water was associated with high probability of switching between choices, while access to alcohol solution led to frequent repeating of the same choice. FINANCIAL SUPPORT: NCN Sonata Bis UMO-2012/07/E/ NZ3/01785 .