Extent of food restriction affects probability but not delay‐based decision‐making
Tighter food restriction makes rats gamble more for uncertain food but leaves their delay tolerance unchanged.
01Research in Context
What this study did
The team put rats on two levels of food restriction. Some rats lived at 85% of their free-feed weight. Others lived at 90%.
Each rat then chose between two levers. One lever gave a small food pellet for sure. The other gave a bigger pellet, but only sometimes. The delay to the bigger pellet also changed across trials.
The goal was to see if tighter food restriction changes how rats gamble with food or how long they are willing to wait.
What they found
Tighter restriction made the rats pick the risky lever more often. In other words, hungry rats chased the chance of a bigger meal.
Yet the same hunger did not change how long they would wait. Their delay discounting stayed flat.
Whether the lab fed the rats once or twice a day made no difference, as long as body weight was the same.
How this fits with other research
Kelly (1973) saw the opposite: hungrier rats worked less on an avoidance task and took more shocks. Together the papers show that food restriction can either raise or lower operant work, depending on the task.
Jarmolowicz et al. (2017) studied obese Zucker rats and found no drop in delay discounting. Tapp et al. now add that lean, food-restricted rats also keep the same delay choices. Across metabolic states, delay discounting looks stable.
Torres et al. (2011) used the same adjusting-delay setup to map indifference points. The new data extend that work by showing those indifference points do not shift when you tighten weight control.
Why it matters
If you run animal studies, match weight targets to the task. Probability-based choice tasks need tight control because hunger biases risk taking. Delay tasks do not, so you can ease restriction and still get clean data. Check your feeding schedule only if body weight drifts; the schedule itself does not matter.
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Join Free →Set your rats to 90% weight instead of 85% if you are testing delay discounting; you will get the same data with kinder hunger levels.
02At a glance
03Original abstract
Rodent studies on decision-making often use food rewards and food-restrict subjects in order to motivate performance. However, food restriction has widespread effects on brain and behavior, which depend on factors including extent of restriction and feeding schedule. These factors are well recognized for their effects on motivation, but may also cause effects on decision-making independent of motivation. We examined how the degree of weight-based food restriction in rats influenced decision-making on the probability and delay discounting tasks. Additionally, we examined how the method of food restriction (consistent amount vs. time constrained feeding schedule) influenced decision-making. Our results showed that the degree of weight-based food restriction significantly altered probability, but not delay discounting, and that these effects were not entirely explainable by differences in motivation. Additionally, the method of food restriction did not significantly influence discounting when animals were within the same range of weight-based restriction. Together, our findings suggest that the degree of food restriction may modulate the neural circuitry responsible for selective aspects of decision-making related to probability. Further, these data support the need for tight control and reporting of weight and feeding in studies relying on food restriction, and suggest that the effects of food restriction may be broader than previously considered.
Journal of the Experimental Analysis of Behavior, 2020 · doi:10.1002/jeab.624