Potency of food deprivation intensity cues as discriminative stimuli.

Rats were trained to use stimuli arising from 0 and 24 hr without food as discriminative signals for shock. In Experiment 1, one group was shocked under 0-hr food deprivation and not shocked under 24-hr food deprivation. Another group received the reverse contingency. The groups received only 3 training trials under each deprivation level. Learning was revealed in a test phase when greater extinction of freezing was observed under the nonshocked than under the shocked deprivation level for both groups. A similar pattern of results was obtained in Experiment 2 when auditory cues were also relevant throughout training. Furthermore, prior training with food deprivation cues seemed to reduce learning about auditory cues subsequently trained in compound with deprivation stimuli. The results indicate that food deprivation intensity cues can be potent discriminative stimuli. The idea that deprivation cues function as conditioned modulatory stimuli cues is also discussed.     

Combination of drive and incentive

This experiment was designed to investigate the combination of drive and incentive as determinants of performance. Nine groups of rats were trained to press a bar under three levels of food deprivation (12, 24 and 36 hr.) and three incentive conditions (1,2 and 3 pellets). Response strength was estimated by counting the number of responses with a latency of 1 sec. or less during five 20 trial sessions. The results indicated that response strength increased with hours of deprivation and with amount of food reward. Significant interactions between sessions and drive, and sessions and incentive provided additional support for the multiplicative combination of H (habit) and D (drive) and H and K (incentive). The lack of significant interaction between D and K was interpreted as supporting the hypothesis that D and K combine additively rather than multiplicatively.     

Interactive effects of deprivation in the albino rat

The interactive effects of feeding and drinking schedules were investigated in three experiments. Twenty-four hour water-deprived rats consumed their entire obligatory water intake prior to feeding, whereas 24-hr food-deprived rats consumed only small quantities of food prior to drinking. This drinking was apparently due to a shift of water stores rather than an actual negative water balance. Experiment 3 investigated the effects of 24, 48, or 72 hr of water, food, or total deprivation. Water-deprived rats did not adequately suppress food intake and became thirstier than totally deprived rats. The effects of total deprivation were essentially identical to those of food deprivation. These experiments indicate the degree to which deprivation schedules impose restrictions on the reinforcement parameters of behavioral experiments.     

The Effects of a Single Dose of Pemoline on Performance and Mood During Sleep Deprivation

Stimulants may be used to improve performance during sleep deprivation. A previous study found that multiple doses of pemoline (37.5 mg every 12 hr) during 64 hr of sleep deprivation improved speed of cognitive performance with variable effects on accuracy. In this study, a single dose of 37.5 mg of pemoline was administered once during the 2nd of 2 nights of sleep deprivation. With this administration schedule, participants showed improved performance, predominantly on accuracy (percentage correct) measures. Effects on speed were minimal. The three tasks which were primarily tests of reaction time showed no stimulant effects. Pemoline had no negative effects on performance, in contrast to the findings of the multiple-dose study. Administration at the time of maximum need (previous sleep deprivation added to the effects of the circadian low period for performance and alertness) may explain the change in effects.     

Shifts in deprivation level: Different effects depending on amount of preshift training

Seventy-two male albino rats were trained to perform an instrumental running response, half at high deprivation and half at low. At Trials 23, 75, and 105 a third of the animals from each of the original groups were shifted to the opposite deprivation level. All shifts from high to low deprivation produced a significant decrease in performance; all shifts from low to high, a significant increase. After the early shift, performance was characterized by a residual effect of preshift deprivation level in which shifted groups gradually approached the new levels. After each of the later shifts, performance levels diverged sharply in what appeared to be both positive and negative contrast effects. The results were discussed in the framework of incentive motivation theory.     

The effect of hunger on water intake in rats

Although reciprocal inhibition between eating and drinking has been postulated, the commonly observed reduction of water intake by hungry rats may not be due to any direct inhibitory mechanism. In one experiment rats deprived of food for 24 hr. and then injected with 2 ml. of NaCl drank the same as rats that had received food ad lib. In the second experiment a stomach load of 10 ml. of water 3 hr. before the salt injection was designed to abolish any water deficit that might have occurred during food deprivation had there been inhibition of drinking by hunger. Here again rats deprived of food did not drink less than undeprived animals. In fact the hungry rats drank slightly but significantly more. This phenomenon may be related to the observation confirmed here that during food deprivation rats excrete about twice as much rather dilute urine as during ad lib food intake. This seems to indicate that though in general food deprived rats drink less than normal they actually drink more than they need. Schedule induced polydipsia also occurs during food deprivation and this too makes it unlikely that water-intake is actually inhibited during hunger.     

A study of misbehavior: token reinforcement in the rat

The purpose of this research was to investigate the phenomenon of misbehavior described by Breland and Breland (1961). Rats were trained to obtain ball-bearings and drop them in a hole for food or water reinforcers. In confirmation of the Brelands' observation, many subjects were slow to deliver the balls, and frequently attempted to chew them before they were dropped. A series of four experiments, in which the same rats were used throughout, showed that delivery times tended to be longer with food than with water, and that these times increased when nylon balls were substituted. The effect of motivational level was investigated by varying both deprivation and amount of prefeeding; no effect on delivery time was detected, although other measures of performance were affected by motivational factors. Similar results were obtained in a final experiment that employed a new set of naive subjects. The studies demonstrated that misbehavior can be studied in an experimental situation, and the results supported an analysis in terms of competition between stimulus-reinforcer and response-reinforcer contingencies. The question of why such effects have not been reported in previous token reinforcer studies was unanswered.     

Deprivation level affects extinction of a conditioned taste aversion

Hooded rats were conditioned to avoid drinking saccharin by following exposure to saccharin with injection of cyclophosphamide, a drug that produces visceral upset. Extinction trials were then given by presenting saccharin without cyclophosamide injections with the rats under low (10 hr) or high (23 hr) fluid deprivation. The aversion extinguished in fewer trials in rats under high deprivation.     

Effects of sleep deprivation on free-operant avoidance

Two studies examined effects of sleep deprivation on free-operant avoidance by rats. In Experiment 1, a 5-s shock-shock (SS) interval and 20-s response-shock (RS) interval produced baseline performances, which were reestablished after each experimental manipulation. Once baselines were established, animals were exposed to 24, 48, or 96 hr of sleep deprivation and equivalent periods of home cage and food restriction as a control condition. Compared to baseline, sleep deprivation increased response rates by increasing the proportion of brief interresponse times (IRTs); response rates changed little in the control conditions. Percentage of shocks avoided did not systematically change across conditions. In Experiment 2, the RS interval was manipulated (10, 20, and 40 s), while the SS interval (5 s) and level of sleep deprivation (48 hr) were held constant. Across RS intervals, sleep deprivation increased response rates via a shift toward brief IRTs. In addition, sleep deprivation increased the percentage of shocks avoided as an inverse function of RS intervals.     

Deprivation and satiation: The interrelations between food and wheel running

Two experiments were designed to assess whether depriving rats of food would increase the reinforcement effectiveness of wheel running (Experiment 1) and whether satiation for wheel running would decrease the reinforcement effectiveness of food (Experiment 2). In Experiment 1, a progressive-ratio schedule was used to measure the reinforcement effectiveness of wheel running when rats were deprived or not deprived of food. Completion of a fixed number of lever presses released a brake on a running wheel for 60 s, and the response requirement was systematically increased until the rat stopped pressing or until 8 hr had elapsed. The ratio value reached (and the total number of lever presses) was an inverted-U function of food deprivation (percentage body weight). In Experiment 2, when wheel running preceded test sessions, fewer food-reinforced lever presses were maintained by the progressive-ratio schedule, and responding occurred at a lower rate on a variable-interval schedule. An interpretation of these results is that deprivation or satiation with respect to one event (such as food) alters the reinforcement effectiveness of a different event (such as access to wheel running).     

Competitive fighting in the rat.

Competitive fighting was obtained in pairs of like-sexed laboratory rats by placing a single piece of food into the food hopper following 48 hr. of food deprivation. The fighting was characterized by offensive sideways posture, full aggressive posture, and bite and kick attack. Tests were conducted at 110-120 days of age on pairs of animals that had been housed together since weaning. Fighting was more frequent in pairs consisting of nonlittermates than in pairs of littermates, and it was equally frequent in male and female pairings. Probability of fighting was enhanced by prior experience with food deprivation, and attack was most often initiated by the heavier animal of the pair.     

A comparison of operant licking and lever pressing in the rat

Two groups of rats were trained on a signaled, free-operant, avoidance procedure to lick or to lever press in order to avoid shock while water-deprived or satiated and, in the case of licking, while ingesting deionized water, isotonic saline, or 10% sucrose. The most effective avoidance licking occurred while the rats were water-deprived and ingesting 10% sucrose. Water deprivation level had no effect on lever pressing for shock avoidance. Two other groups of rats were operantly conditioned to lick or to lever press for food pellets while waterdeprived or satiated and, in the case of licking, while ingesting deionized water or 10% sucrose. The most effective licking for food reinforcement occurred while the rats were water-deprived and ingesting 10% sucrose. Water deprivation level had no effect on lever pressing for food reinforcement. The data indicated that effective operant licking must be supported by factors related to water regulation and taste palatability.     

Effects of opiate antagonists on spatial memory in young and aged rats

The effects of post-training opiate antagonist administration on spatial memory were assessed in young and aged male Long Evans rats. In Experiment I rats were trained to visit each arm of an eight-arm radial maze once in a session to obtain a food reward placed at the end of each arm. During training aged rats required significantly more trials to achieve criterion performance when compared to young mature rats. However, administration of the opiate antagonist naloxone (2.0 mg/kg) immediately after each training trial did not significantly alter the rate of achieving accurate performance in either age group. In Experiment II young and aged rats that were previously trained to a comparable criterion on the radial maze were tested on the same maze apparatus in novel spatial environments. When animals were exposed to novel spatial information, the effects of post-trial opiate antagonists were examined using a within-subjects counter-balanced design. In Experiment IIa naloxone (2 mg/kg) enhanced the performance of both young and aged rats. In Experiment IIB naltrexone (1.0 mg/kg) was found to have a comparable effect of enhancing the performance of both age groups. In addition, in Experiment IIb a significant age-related deficit was found in rats tested in novel spatial environments. These results indicate that opiate antagonists are capable of improving memory for new spatial information in both young and aged rats on a task that is sensitive to behavioral deficits during normal aging.     

The Isolation of Motivational, Motoric, and Schedule Effects on Operant Performance: A Modeling Approach

Dissociating motoric and motivational effects of pharmacological manipulations on operant behavior is a substantial challenge. To address this problem, we applied a response‐bout analysis to data from rats trained to lever press for sucrose on variable‐interval (VI) schedules of reinforcement. Motoric, motivational, and schedule factors (effort requirement, deprivation level, and schedule requirements, respectively) were manipulated. Bout analysis found that interresponse times (IRTs) were described by a mixture of two exponential distributions, one characterizing IRTs within response bouts, another characterizing intervals between bouts. Increasing effort requirement lengthened the shortest IRT (the refractory period between responses). Adding a ratio requirement increased the length and density of response bouts. Both manipulations also decreased the bout‐initiation rate. In contrast, food deprivation only increased the bout‐initiation rate. Changes in the distribution of IRTs over time showed that responses during extinction were also emitted in bouts, and that the decrease in response rate was primarily due to progressively longer intervals between bouts. Taken together, these results suggest that changes in the refractory period indicate motoric effects, whereas selective alterations in bout initiation rate indicate incentive‐motivational effects. These findings support the use of response‐bout analyses to identify the influence of pharmacological manipulations on processes underlying operant performance.     

Insulin, exercise, and dietary effects upon behavioral thermoregulation in albino rats

The objectives of this exploratory research were to assess the effects of insulin preparations (Humulin-regular and NPH) on operant behavior reinforced by schedules of microwave radiation in a cold environment and to measure changes in this thermoregulatory behavior as a function of exercise and food deprivation. Eight albino rats were conditioned to regulate their thermal environment with 6-sec. exposures of microwave (MW) radiation (SAR = 0.34 Watts/kg/(mW/cm2) under FR-1 and FR-10 schedules. Regular-insulin and NPH-insulin sessions were administered alternately with saline-control sessions for 8-hr. durations. Exercise in an activity wheel and 48 hr. of food deprivation (diet) were additional independent variables used to alter thermoregulation. Three randomized-block analysis of variance designs with repeated measures showed that insulin preparations resulted in a suppression of operant responding for heat, yet food deprivation increased rates of microwave responding. These data are interpreted in terms of functional relationships between ambient temperature changes, core body temperature, blood glucose fluctuations, and operant behavior.     

Abdominal vagotomy disrupts food-related drinking in the rat

Rats with complete subdiaphragmatic bilateral transection of the abdominal vagus (Vgx-C) showed disordered food-related drinking when drinking water in temporal association with a meal of dry food after 5-hr food deprivation and when drinking water in association with a liquid meal after 24-hr food deprivation. The Vgx-C rats drank after significantly longer latencies and drank significantly less water in 1 hr than did sham-vagotomized (Sham) rats after eating the same size meal (solid or liquid) as Shams. Rats with incomplete vagal transection (Vgx-I) ate and drank like Shams. Water intake of Sham and Vgx-I rats correlated positively with the meal size of solid food, but the water intake of Vgx-C rats did not. The failure of Vgx-C rats to drink water normally when food was ingested was not due to failure of a food stimulus to reach the intestine, because Vgx-C and Sham rats emptied equivalent volumes of liquid food from the stomach into the intestine within 10 min of food entering the stomach. These results indicate that the abdominal vagus is an important neurological substrate for food-related drinking in the rat.     

Variable-interval reinforcement schedule value influences responding following REM sleep deprivation

The effects of rapid-eye movement sleep deprivation (REMSD) in rats were studied in relation to variable-interval (VI) reinforcement schedule value. Initially, lever pressing was maintained on a VI 30-s schedule of food pellet delivery. After a baseline was established, rats were repeatedly exposed to 96 hr of REMSD and control conditions of an equivalent duration. Responding decreased following REMSD but not after exposure to control conditions. Lever pressing was then maintained on a VI 15-s schedule of food pellet delivery and exposure to the REMSD and control conditions was repeated. Under this condition following repeated REMSD exposures, rates of lever pressing became similar to baseline responding. A VI 30-s schedule of food pellet delivery was then reinstated and REMSD and control conditions were repeated. Lever pressing following exposure to the REMSD condition decreased for 3 of 4 rats. Results suggest that VI schedule value influences the effects of REMSD on responding.     

Consolidation of Memory for Odor–Reward Association: β-Adrenergic Receptor Involvement in the Late Phase

Experimentally naive rats can learn rapidly to discriminate among three odors to obtain food reinforcement. After three massed trials, they show almost errorless performance. This task has proved to be useful in studying time-dependent postacquisition intracellular processes necessary for long-term memory. The present experiments evaluated the temporal dynamics of the role of β-noradrenergic receptors in long-term consolidation. Rats were implanted with intracerebroventricular cannulae and trained in a single session to find reinforcement in a hole in a sponge impregnated with a particular odor. Injections of the β-receptor antagonist timolol were made at 5 min, 1, 2, or 5 hr after training. Memory and relearning ability were evaluated 48 hr later. Rats treated with timolol 2 hr after training showed a memory deficit at the retention test, but were able to relearn the task normally. Injections at the earlier or later time points were ineffective. The results reinforce previous observations with systemic injections that β-noradrenergic receptors are involved in the late phase of memory consolidation and suggest a critical time window during which they are necessary. The time window is compatible with the current view that long-term memory depends on late involvement of the cAMP cascade leading to new protein synthesis necessary for synaptic reorganization.     

The role of the instrumental contingency in the motivational control of performance

In four experiments we investigated an irrelevant incentive effect based upon a transition from hunger to thirst. Hungry rats were trained to lever press either for sucrose solution or for food pellets before performance was tested in extinction while they were thirsty. Reinforcer-specific motivational control was found in the first experiment in that the animals pressed the lever more on tests following training with the sucrose solution rather than with food pellets. Moreover, this effect was seen only when testing was conducted following water, but not following food deprivation. The outcome of the remaining experiments suggests that this motivational control is not mediated by the instrumental contingency between lever pressing and the sucrose reinforcer during training. In these studies lever pressing and chain pulling were reinforced concurrently, one with sucrose and the other with food pellets, in order to equate the noninstrumental functions of the incentives. Following this training, lever pressing in extinction under thirst was unaffected by the type of incentive used as its reinforcer during training.     

Irrelevant incentive learning during instrumental conditioning: The role of the drive-reinforcer and response-reinforcer relationships

Four experiments investigated the processes by which a motivationally-induced change in the value of the training reinforcer affects instrumental performance. Initially, thirsty rats were trained to lever press for either a sodium or non-sodium solution. In Experiment I sodium-trained rats responded faster in extinction following the induction of a sodium appetite, but not following either food or water deprivation. Thus, enhanced extinction performance depends upon the relevance of the training reinforcer to the test drive state. The remaining experiments examined the role of the instrumental contingency. Animals received response-contingent presentations of one solution alternated either within (Experiments II and III) or between sessions (Experiment IV) with non-contingent presentations of another solution. Neither procedure yielded convincing evidence that contingent sodium presentations generated more responding in extinction under a sodium appetite than did non-contingent sodium presentations. On the basis of these results, we argue that the instrumental contingency itself does not play a major role in this irrelevant incentive effect.