Polydipsia induced by intermittent delivery of salted liquid foods.
Salty liquid food, delivered every two minutes, pushes rats into intense schedule-induced drinking.
01Research in Context
What this study did
Researchers gave rats salty liquid food every two minutes. They wanted to see if the salt would make the rats drink extra water between feedings.
The team tested different salt levels and different time gaps. They watched how much water each rat lapped up after every sip of food.
What they found
The salted food triggered heavy drinking. The biggest effect hit at the 120-second schedule.
Plain food did not create the same water binge. The salt, plus the steady two-minute rhythm, produced classic schedule-induced polydipsia.
How this fits with other research
Smith (1967) already showed liquid diets can spark polydipsia, but used unsalted formula. Bacon-Prue et al. (1980) now proves the key ingredient is salt, not texture.
Nelson et al. (1978) doubled water intake by stretching the schedule from 15s to 60s. The new study pins the peak at 120s, fitting neatly on the same upward curve.
Blackman (1970) ruled out accidental reinforcement as the driver. A et al. agree: the clock, not the lever, controls the drinking burst.
Why it matters
If you run preference assessments or token economies, remember that adjunctive behaviors can pop up whenever reinforcers arrive on a clock. Watch for extra water trips, pacing, or other collateral behavior when you space deliveries around two minutes. Adjust schedule length or reinforcer type to keep the session on track.
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02At a glance
03Original abstract
Food-deprived rats given constant access to water were exposed to fixed-time presentations of soybean milk and diluted sweetened condensed cows' milk. In some conditions these liquid foods were adulterated with varying amounts of sodium chloride. Under a fixed-time 30-sec schedule of food delivery, little water was consumed when the food was soybean milk alone, or soybean milk with sodium chloride added in concentrations of .9, 1.8, or 3.6%. However, schedule-induced polydipsia appeared when soybean milk adulterated with 7.2 or 14.4% sodium chloride was delivered under this schedule. When soybean milk containing 7.2% sodium chloride was presented under fixed-time 15-, 30-, 60-, 120-, and 240-sec schedules, schedule-induced drinking increased with the fixed-time value from 15 to 120 seconds, and decreased at 240 seconds. Like soybean milk, diluted sweetened condensed milk delivered under fixed-time schedules of 30, 60, and 120 seconds failed to evoke schedule-induced polydipsia, but did so when adulterated with 7.2% sodium chloride. Drinking induced by salted liquid foods resembled the polydipsia engendered by spaced dry-food presentations in several ways, including temporal relation to food delivery, persistence within and across sections, sensitivity to interfood interval, and magnitude relative to intake evoked by bulk-food presentation.
Journal of the experimental analysis of behavior, 1980 · doi:10.1901/jeab.1980.33-337