ORDER EFFECTS ALTER WORK EFFORT IN RAT MODEL OF FREE CHOICE

Examining the external and internal factors involved in motivation to work using animal models (e.g., rodent model) is an important question for psychological and behavioral sciences. The role of effort on work output has been a key variable under investigation. Previous work is highly limited, showing animals inconsistently choose higher effort work options and generally find effort aversive. A goal of the present study is to increase preference for effortful work. The methods included utilizing controlled testing experiences originating with completion of high effort options for greater reward. Our procedures tested choice for different effort options using a free-foraging task that allows animals to self-pace behavior and explore within a larger testing environment. Animals chose between a high effort option (5 lever press) with shifting reward outcome value either food magnitude descending (5, 4, 2, 1 pellets) or ascending (1, 2, 4, 5 pellets) over a 4-week period. Each week the alternative option was low effort and low reward (1 lever press for 1 pellet). Work motivation/output was determined using analysis of high effort reward discrimination, preference and incentive contrast between testing weeks. An order effect was observed with animals working harder and choosing the greater effort option significantly more when rewards were in descending order of magnitude as compared to ascending order. Further analysis will focus on a set of dependent variables including place preference, approach and consumption measures. In addition, the results allow for an analysis of error rates when obtaining reward options in different choice contexts. These findings suggest that rats experiencing higher levels of work initially will continue to choose a higher effort work option more often even when costs of food reward increase compared to a lower effort option. Results can lead to novel methods for understanding key factors involved in work aversion or justification, testing the impact of drugs of abuse on motivation, and exploring brain substrates of reward processing related to effort.