Combined effects of food deprivation and food frequency on the amount and temporal distribution of schedule-induced drinking.

Luis and team worked with lab rats on a fixed-interval food schedule. They asked two questions: Does food deprivation change how much the rats drink between pellets? Does the time between pellets matter too?

They tested four hunger levels (0, 8, 16, 24 h without food) and three pellet-to-pellet times (30 s, 120 s, 240 s). A lick sensor recorded every tongue touch to a water spout.

Hungrier rats licked more. The biggest jump came between 16 h and 24 h of deprivation. Shorter pellet gaps (30 s) also produced the most licks.

Timing changed with hunger. Well-fed rats drank right after a pellet. Starved rats spread the same drinks across the whole interval, almost like they were pacing themselves.

Anger et al. (1976) showed drinking peaks when pellets arrive every 120 s. Castilla et al. (2013) found the same sweet spot, but only in mildly hungry rats. At 24 h of deprivation, even the 30-s schedule drove high drinking, so hunger widens the effective range.

Johnson et al. (1994) saw less drinking when water was offered close to the next pellet. Luis saw the opposite: starved rats kept drinking late in the interval. The difference is procedure—R offered one timed sip; Luis let rats drink freely, showing adjunctive patterns can override probe timing.

Together, these studies draw the same curve: drinking rises, peaks, then falls as the interval grows. Hunger lifts the whole curve and flattens it, so the peak is less sharp.

If you run FI schedules in a classroom or animal lab, know that hunger and interval length team up. A kid on a lean schedule who skipped lunch may show more water-cooler trips or other adjunctive habits. Track these side behaviors; they can mask or mimic the main target. Try offering a small snack before sessions or lengthening the interval if adjunctive behavior interferes.