Pellet Delivery Research Articles

Reinforcement omission, non-contingent reinforcement, and limbic lesions in rats

Two groups of six albino rats were given lesions of the septum and dorsal hippocampus respectively. Under an FI 1 min schedule of food reinforcement, septal rats lever pressed at significantly higher response rates than intact controls. Under a modified FI 1 min schedule during which food pellets were occasionally omitted, every subject made more responses in intervals following omissions than in those following pellet deliveries, but rats with hippocampal lesions showed a larger increase in response rate than either controls or septals, which did not differ. In Experiment 2, half of these subjects were subjected to experimental extinction, and half provided with noncontingent reinforcement at 1 min intervals. Both procedures decreased responding, but only under extinction did the experimental groups show slower decreases than the controls. Although these data provide a clear double dissociation for septal and dorsal hippocampal lesions, they present substantial difficulties for both “disinhibition” and “perseveration” theories of septal and hippocampal function.

EFFECTS OF RESPONSE‐DEPENDENT AND INDEPENDENT ELECTRIC SHOCK ON SCHEDULE‐INDUCED POLYDIPSIA

In Experiment I, lever pressing by rats was maintained by the delivery of food pellets under a 45-sec fixed-interval schedule. Fixed-time 180-sec and fixed-interval 180-sec schedules of shock delivery were systematically superimposed on the baseline food schedule to study effects on schedule-induced water intake. Response-dependent shock had little, if any, effect on water intake, whereas shocks independent of lever pressing attenuated fluid intake. In Experiment 2, rats received food pellets under a fixed-time 60-sec schedule. Electric shock delivered concurrently under a variable-time 180-sec schedule, but never while the animal was licking or within 5 sec after licking terminated, led to similar attenuation of water intake. These findings suggest that schedule-induced polydipsia is sensitive to differences in the functional properties of response-independent and dependent electric shock.

UBIQUITY OF SCHEDULE‐INDUCED POLYDIPSIA1

Spaced feeding of individual food pellets to food-deprived rats induced excessive drinking after pellet delivery if water was continuously available. When access to water was restricted to a portion of the inter-pellet interval, and competition from food-reinforced bar pressing was removed, excessive drinking occurred whenever drinking was possible. This finding extends the generality of accounts of excessive behavior that implicate induction by apparently unrelated scheduling characteristics of the environment.

Social hierarchy in monkeys ( Macaca mulatta) modified by chlordiazepoxide hydrochloride

The effects of intramuscular injection of chlordiazepoxide hydrochloride (Librium) on individual and social behaviour was tested on a colony formed by four rhesus monkeys. Spontaneous mobility of each animal was continuously recorded by telemetry. Behaviour was quantified during three periods of 15 min each: first control (C I), delivery of pellets to an elevated feeder (CP) and second control (C II). Results were as follows: Administration of 5 mg/kg to the dominant monkey produced a 50 % reduction of spontaneous mobility which lasted for several hours. In addition there was some decrease of walking, a reduction of feeding, increase in lying and complete absence of grooming. The number of attacks increased significantly during C I, was not modified during CP and diminished during C II. It is postulated that chlordiazepoxide produced a decrease of normal signs of dominance and increased the challenge and replacement of the non-drugged animal against the authority of the leader of the group. Increasing the dose injected into the dominant animal to 10 mg/kg produced a greater and more lasting reduction of spontaneous mobility, with some cumulative effects, a reduction of walking during C I and C II, an absence of mounting and grooming and an increase of lying. Attacks also increased during C I and CP. while disappearing during C II. After the fifth injection there was a change in the hierarchical structure of the colony, with the dominant drugged animal dropping position, and the leadership of the group being taken by the monkey which was number 2. Injection of 10 mg/kg of chlordiazepoxide into the lowest ranking monkey, did not modify his hierarchical position, nor did it produce any signs of hostility. His behaviour was. however, modilied, decreasing spontaneous mobility and walking, abolishing grooming and increasing lying down. In the investigation of psychoactive drugs the social status of the experimental animal should be taken into consideration as an important factor in the interpretation of results.

Licking response distributions associated with the acquisition of schedule-induced polydipsia

The relation between drinking and pellet delivery was examined in a rat that acquired polydipsia when it was exposed to a free fixed-interval (FFI) 50-sec food (Noyes 45-mg pellets) schedule. A distributional analysis of responding in the interpellet interval indicated that drinking, which was originally distributed equally throughout the interpellet interval, became concentrated predominantly as a postpellet event within the first FFI session. The redistribution of drinking as a postpellet event was followed by an increase in water consumption, with asymptotic water intake occurring by the fourth FFI session. These results indicated that schedule-induced polydipsia cannot be attributed to adventitious food reinforcement.

Developmental analysis of schedule-induced polydipsia.

In a developmental analysis of schedule-induced polydipsia (SIP), 8 female, albino rats were exposed to either a FI-60-sec. or a VI-60-sec. reinforcement schedule with 4 Ss in each group. Results indicated that the adventitious reinforcement explanation for SIP is not tenable, since licks did not occur with equal probability in all periods of the interpellet interval during SIP development; lick bursts coming in contact with pellet deliveries were a result rather than a cause of SIP; and SIP developed more slowly on the VI than on the FI schedule.

AN INEXPENSIVE FEEDER FOR RAPID DELIVERY OF MONKEY PELLETS

AN INEXPENSIVE FEEDER FOR RAPID DELIVERY OF MONKEY PELLETS

Avoidance response rates during a pre-food stimulus in monkeys.

Free-operant avoidance responding was maintained by a shock avoidance schedule in three monkeys. The frequency of avoidance responses during a stimulus terminated by response-independent food pellet presentation was dependent upon the method of pellet delivery. Avoidance rates were relatively increased when food retrieval responses followed pellet delivery. Avoidance rates were decreased when retrieval responses preceded pellet delivery.

Evaluation of a polydipsia technique to induce alcohol consumption in monkeys.

The observation that the intermittent delivery of dry food pellets is accompanied by consumption of large quantities of water in the rat was first described by Falk in 1961 (4) and this phenomenon was subsequently termed psychogenic or schedule-induced polydipsia. Falk (4) reported that rats maintained at 80 per cent of their free feeding weight, would consume approximately one half of their total weight in water within a few hours when food pellets were presented intermittently. Variations of thirst explanations for this phenomena proved untenable since pre-session water loading did not eliminate polydipsic drinking (8) and dry food was neither necessary or sufficient for the induction of polydipsia. Intermittent delivery of small portions of a standard liquid monkey diet were equally effective in producing excessive drinking (7). Superstitious chaining, i.e. the adventitious reinforcement of drinking within the inter-pellet interval also fails to account for polydipsia (5,33). A number of factors have been identified that contribute to the magnitude of the effect such as an inter-pellet interval of more than 45 sec (6), small food portions (7) and weight reduction (8). However, Falk (9) has emphasized that reinforcement schedules do not elicit polydipsic drinking, but rather the behavior develops gradually and can be attenuated by weight increase even when response rates and food intake stay the same. The power of the procedure is illustrated by the fact that comparable levels of fluid ingestion are not achieved by other experimental manipulations such as water deprivation, heat stress or osmotic loading in rat (8). Falk describes schedule-induced polydipsia as a form of adjunctive behavior and concludes that no adequate physiological or behavioral explanation for the phenomena has yet been advanced (8,9).

Schedule-induced polydipsia with nutritive and nonnutritive reinforcers

Eighteen Charles River (cd) male rats were conditioned to drink water polydipsically by the delivery of food pellets on FFI 45 sec, and then, varying percentages of sweetened nonnutritive pellets were substituted for the nutritive pellets. The mean volume of water ingested decreased with decreased nutritive content of the pellets, suggesting a relationship between schedule-induced polydipsia in the rat and the nutritive content of the reinforcer.

Reinforcement of ethanol consumption in rats by an increase in the frequency of food-pellet delivery

An increase in the frequency of food-pellet delivery to four food-deprived rats was made contingent upon drinking either distilled water or a 9% (v/v) ethanol solution. In spite of the contingency of a minimum interval of 3 sec between drinking the reinforced liquid and pellet delivery, an increase in the frequency of pellet delivery from one per 120 sec to one per 15 sec on the average acted as a positive reinforcer for drinking that liquid associated with the greater pellet frequency.

The effects of alcohol concentration on schedule-induced alcohol drinking

Rats were made polydipsic for water by the free delivery of food pellets on a fixed-time 1-min schedule. Alcohol concentrations of 2.5%, 5.0%, 7.5%, and 10% were then substituted for the water. An inverse relationship between fluid consumption and alcohol concentration was observed; however, the function relating grams of absolute alcohol consumed to concentration increased monotonically.

Maximization of pellet density by rats in a two-choice operant situation

Four food-deprived experimentally naive male albino rats were given a choice between two levers. Pressing either lever after a food pellet delivery started a time period of variable length which ended with a pellet delivery, providing neither lever had been pressed in the immediately preceding 5 sec. Pressing one of the levers delivered a pellet more often than did pressing the other. Responses were generally allocated to the lever producing pellets more frequently. We conclude that rats can distinguish between pellet densities and will maximize pellet densities even when no response is immediately reinforced by being followed by a pellet.

POSITIVE CONDITIONED SUPPRESSION: EFFECTS OF CS DURATION1

During a brief conditioned stimulus (15 or 30 sec) that terminated with the response-independent delivery of banana pellets, operant responding reinforced by other food pellets according to a variable-interval schedule of reinforcement was suppressed in the squirrel monkey. Conditioned stimuli of longer duration (1, 2, and 3 min) did not reliably affect the rate of operant performance. Brief conditioned stimuli generated homogeneous response patterns of nearly complete suppression. Increasing the CS duration did not enhance responding, as previously reported, but led to alternate bursting and pausing, which suggested a loss of control by the conditioned stimulus. The results suggest that the magnitude of "positive" or "negative" conditioned suppression reflects the strength of the classical conditioning process.

Ethanol consumption by rats on a differential probability of reinforcement schedule

Four white rats were trained to drink 9% (ν/ν) ethanol by programming drinking to change the frequency of food pellet delivery from once every 2 min to once every 15 sec on the average. When water and ethanol were both available and only ethanol drinking changed the frequency of pellet delivery, the animals switched from drinking water on the preferred side to drinking ethanol on the nonpreferred side.

Facilitation of avoidance responding in white rats during a stimulus preceding food.

The lever pressing of four food deprived male albino rats was maintained by a modified free-operant shock-avoidance procedure. Periodically a clicking sound (CS) was presented. Towards the end of the CS, 10 sucrose pellets (US) were delivered provided S did not press in a given period immediately preceding food delivery. Three independent variables were studied: level of deprivation, kind of avoidance schedule and length of the no-response period preceding pellet delivery. Response facilitation during the CS was found at certain combinations of the independent variables.

Response rate and varied reinforcement: Reinforcers of different strengths

Twelve rats were trained to lever press on a multiple schedule with the delivery of pellets, sucrose, or pellets or sucrose correlated with the three legs of the schedule. The “pellet-or-sucrose” condition, i.e., varied reinforcement, produced the highest response rates. These results replicate, in a within-Ss design, the previous findings of a between-group experiment.

Drinking response distributions associated with a 4% sucrose FFI food schedule

Polydipsia was produced in two female rats when they were exposed to a FFI 40 sec. 4% sucrose pellet food reinforcement schedule. An analysis of the inter-pellet drinking distribution of both Ss indicated that drinking followed, rather than preceded pellet delivery. This result was interpreted as further evidence for a prandial interpretation of schedule-induced polydipsia.

The development of water drinking on a dry-food free-reinforcement schedule

Rats were given a food pellet every 60 sec., not contingent on operant responding. All rats developed over days a pattern of prolonged water drinking following delivery of food pellets. One of the rats, whose operant-level lever pressing was recorded concurrently with licking, developed a complex pattern of drinking and bar pressing which persisted even after a 5-sec. delay of reinforcement for bar presses was introduced.

A Semi-Automated Device for the Delivery of Food Pellets to Runway Goal Boxes

Researchers using runways for animals often wish to vary magnitude of reward between Ss or within Ss from trial to trial. A fully automated system would be costly and complex, therefore the usual method has been to place the pellets directly in the food cup by hand even though the method is awkward and time consuming. One possible solution is the use of a commercial pellet dispenser operated by a push button. Such a system can be made even more effective by adding a telephone dial and single-pole, heavy-duty relay having normally open contacts. With this system any number of pellets up to 10 can be delivered by simply dialing the appropriate digit. The dial is available from several surplus sources and is inexpensive. The standard telephone dial delivers pulses at the rate of 10 per sec. which is well within the operating rate of most commercial pellet dispensers. Most telephone dials emit one more pulse than indicated by the digit dialed, e.g., if one dials the digit 3, four pulses are emitted. This extra pulse can be eliminated by adding an extra finger stop constructed of heavy wire (coathanger wire is excellent) and positioned between the first finger hole and the existing finger stop. The extra finger stop now will stop the rotation of the dial one position short, therefore allowing formation of only the dialed number of pulses. Since the contact points of the dial are not heavy enough to carry the current required by the pellet dispensers, it is best that the dial operate a heavy duty relay which in nlrn operates the pellet dispenser. A fuse of sufficient current rating should be placed in series with the pellet dispenser for protection of the dispenser coil in case any part of the system fails to break the circuit after delivery of a pulse. In alleys or apparatus requiring two goal boxes, two pellet dispensers may be used with one relay simply by adding a single-pole, double-throw switch which can switch the delivery of the pulses to either of the dispensers. Such a system has been used in research by the authors over a long period of time and has been found to be accurate, reliable, and time saving.