Some effects of lick-contingent delays on the development of schedule-induced polydipsia

Reinforcement of schedule-induced drinking in rats by lick-contingent shortening of food delivery

Schedule-induced drinking has been a theoretical question of concern ever since it was first described more than 50 years ago. It has been classified as adjunctive behavior; that is, behavior that is induced by an incentive but not reinforced by it. Nevertheless, some authors have argued against this view, claiming that adjunctive drinking is actually a type of operant behavior. If this were true, schedule-induced drinking should be controlled by its consequences, which is the major definition of an operant. The present study tested this hypothesis. In a first experimental phase, a single pellet of food was delivered at regular 90-s intervals, but the interfood interval could be shortened depending on the rat's licking. The degree of contingency between licking the bottle spout and hastening the delivery of the food pellet was 100 %, 50 %, and 0 % for 3 separate groups of animals. Rats that could shorten the interval (100 % and 50 % contingency) drank at a higher rate than those that could not (0 %), and the level of acquisition was positively related to the degree of contingency. In a second phase of the experiment, all groups were exposed to a 100 % contingency, which resulted in all rats developing high levels of schedule-induced drinking. Licking is enhanced if it hastens reinforcement, and can do so at delay characteristics of those present in studies of schedule-induced drinking, thus supporting the view that adjunctive behavior is an operant.

Punishment of schedule-induced drinking in rats by signaled and unsignaled delays in food presentation

Food-deprived rats were exposed to a fixed-time 60-s schedule of food-pellet presentation and developed schedule-induced drinking. Using an ABA reversal design, three experiments investigated the effects of events then made dependent on licks. In Experiment 1, lick-dependent signaled delays (10 s) in food presentation in general led to decreased drinking, which recovered when the signaled delays were discontinued. The drinking of yoked-control rats, which received food at the same times as those exposed to the signaled-delay contingency, showed much smaller changes. Experiment 2 showed that 10-s lick-dependent signals alone did not reduce drinking. In Experiment 3, when licks produced unsignaled 10-s delays in food there were less marked and more gradual changes in drinking than in Experiment 1, although these effects again were greater than with yoked-control animals. We concluded that both signaled and unsignaled delays functioned as punishers of drinking. These findings support the view that schedule-induced drinking, like operant behavior, is subject to control by its consequences.

Level of response suppression and amphetamine effects on negatively punished adjunctive licking

The purpose of the present study was to investigate whether the level of response suppression is a major determinant of the effect of D-amphetamine on negatively punished adjunctive drinking. Rats were initially exposed to a multiple fixed-time (FT) 30-s FT 30-s food delivery schedule. They were then divided into two groups and subjected to one of two different multiple schedules, FT 30-s FT 45-s or FT 30-s FT 90-s. The FT 45-s and FT 90-s components were signalled by a tone. Comparably high levels of adjunctive licking were observed in both FT 30-s components, intermediate licking levels in the FT 45-s component, and little licking in the FT 90-s component. Licking during the FT 30-s components was subsequently punished by lick-contingent signalled delays (by a blackout) in food delivery. The duration of such delays was adjusted to reduce licking to levels obtained in the FT 45-s or FT 90-s components, respectively for each of the two groups. Punished licking was increased by 0.3 and 1.0 mg/kg of D-amphetamine, an effect that was greater in the FT 30-s FT 90-s group. No increase in licking was observed in the FT 45-s component, but the 1.0 mg/kg dose also increased responding in the FT 90-s component. In general, no statistically significant differences were found between the effects of D-amphetamine on punished and unpunished schedule-induced licking. As licking decreased during the FT 90-s component when the punishment contingency was introduced in the alternate component, the punishment procedure and FT 30-s component were entirely removed. On this occasion, D-amphetamine failed to increase licking induced by the FT 90-s schedule. These results indicate that the level of response suppression might be a good indicator of the degree to which D-amphetamine shows antipunishment effects on adjunctive licking reduced by negative punishment procedures.

Amphetamine increases schedule-induced drinking reduced by negative punishment procedures

RATIONALE

d-Amphetamine has been reported to increase schedule-induced drinking punished by lick-dependent signalled delays in food delivery. This might reflect a drug-behaviour interaction dependent on the type of punisher, because no such effect has been found when drinking was reduced by lick-contingent electric shocks. However, the anti-punishment effect of amphetamine could be mediated by other behavioural processes, such as a loss of discriminative control or an increase in the value of delayed reinforcers.

OBJECTIVES

To test the effects of d-amphetamine on the acquisition and maintenance of schedule-induced drinking reduced by unsignalled delays in food delivery.

METHODS

Rats received 10-s unsignalled delays initiated by each lick after polydipsia was induced by a fixed-time 30-s food reinforcement schedule or from the outset of the experiment. Yoked-control rats received these same delays but independently of their own behaviour. d-Amphetamine (0.1-3.0 mg/kg) was then tested IP.

RESULTS

d-Amphetamine dose-dependently increased and then decreased punished schedule-induced drinking. The drug led to dose-dependent reductions when the delays were not contingent or when they were applied from the outset of training.

CONCLUSIONS

These results support the contention that d-amphetamine has an increasing effect on schedule-induced drinking that has been previously reduced by a negative punishment procedure. This effect cannot be attributed to other potentially involved processes, and therefore support the idea that drug effects on punished behaviour depend on punishment being delays in food or shock deliveries.

Food deprivation and food-delay effects on the development of adjunctive drinking

Twelve rats were food-deprived to 90% or 70% of their free-feeding weights. Food pellets were then delivered every 60 s (Fixed Time 60-s schedule), and the development of adjunctive drinking was measured by the water consumed and the number of licks. For "master" rats, each lick was followed by 10-s delays in food delivery. Yoked control rats received food at the same time as their master rats and independently of their own behavior. At 70% deprivation, both master and control rats developed similar levels of schedule-induced licking, but the master rats drank less water. At 90% deprivation, master animals showed little drinking and licking, but the development of adjunctive drinking was not completely prevented. Drinking by yoked control rats did not differ as a function of deprivation level. In showing that lick-dependent delays in food delivery reduce the asymptotic development of adjunctive drinking as a function of the rats' level of food deprivation, these results support the view that environmental influences on schedule-induced drinking are modulated by motivational factors.

Food-delay duration and the development of schedule-induced polydipsia in rats

Twelve rats were exposed to a schedule that delivered a food pellet every 60 s (fixed time 60 s). The development of schedule-induced polydipsia was measured in terms of the water consumed and the licks per interpellet interval. Every lick by master rats initiated an unsignalled delay of 2 or 50 s in food delivery. Yoked-control rats received food at the same time as their masters, being unaffected by their own licking. Schedule-induced polydipsia developed in master rats exposed to 2-s delays, but more slowly and to a lesser extent than control animals. The development of polydipsia was prevented in master rats exposed to 50-s delays, however. When these delays were discontinued, polydipsia was obtained by master rats. The finding that the effect of the delays was modulated by their duration supports the view that the development of schedule-induced polydipsia is sensitive to control by its environmental consequences.

Varying the temporal placement of a drinking opportunity in a fixed-interval schedule

Three rats, lever pressing for food delivered on a fixed-interval 128-s schedule, were presented with a 16-s opportunity to drink from a retractable water source. The temporal placement of the water probe within the reinforcement cycle was varied sequentially, in steps of 16 s. Although the lever-pressing pattern was modulated by the intercalated water probe, water consumption during the probe itself was a decreasing function of time from the following reinforcer. These results were interpreted as evidence against the notion that schedule-induced drinking is a "ubiquitous" phenomenon and are congruent with results from other "intruded stimulus" experiments.

Selective sensitivity of schedule-induced activity to an operant suppression contingency

The sensitivity of pigeons' schedule-induced activity to operant consequences was studied in two experiments. During a 30-s interval between food presentations, a keylight stimulus brightened incrementally. Stable terminal key pecking and interim locomotor activity developed. An operant "setback" contingency was applied to activity. The contingency arranged for locomotor movements (detected by a nine-panel floorboard) to be followed by a resetting of the keylight brightness to a dimmer value and a 1-s delay of reinforcement (for individual responses). Experiment 1 showed that activity patterns were highly sensitive to their operant consequences. Accompanying key-peck rates were only transiently affected. In Experiment 2, the setback contingency was imposed during restricted portions of the trial, and differential operant control of activity was demonstrated. However, birds in this study produced higher rates of key pecking as activity rates were reduced. These results suggest that although schedule-induced activity arises in response to the temporal arrangement of stimulus events, this behavior may retain considerable sensitivity to response-consequence relations.

Is adjunctive behavior a third class of behavior?

Research during the past 20 years has revealed that intermittent food presentation to a variety of organisms results in an inordinately excessive consumption of water as well as other behaviors including attack, pica, escape, and alcohol consumption. Such behavior has not been thought to be either respondent or operant behavior, but instead has been regarded as a new behavioral category termed "adjunctive behavior." This paper reexamines the rejection of adjunctive behavior as either operant or respondent behavior and concludes that the rejection was premature. This paper also reexamines the argument that there is a unique class of adjunctive behavior and concludes that there is not. It is recommended that given the growing difficulties in maintaining an operant-respondent dichotomy, rather than admitting adjunctive behavior into either of these categories, research efforts should de-emphasize preconceived and outdated notions about categories of behavior and how such behaviors should behave and instead focus on mapping functional relationships between behavior and various procedures for presenting non-contingent stimuli.