Lever For Food Research Articles

D-Amphetamine and punished responding: the role of catecholamines and anorexia.

Rats were trained to press a lever for food on a schedule in which components of variable interval reinforcement (V12') alternated with conflict components in which every response resulted in food delivery and footshock. Low doses of d-amphetamine selectively suppressed responding in the conflict component in a dose-dependent manner, whereas prefeeding suppressed responding in both components. Pretreatment with noradrenergic blocking agents (propranolol, phentolamine and phenoxybenzamine) did not diminish the suppressant effect of d-amphetamine, but this effect was reduced by pretreatment with alpha-methyl-para-tyrosine methylester and dopamine blockers (spiroperidol, haloperidol and clozapine) indicating that d-amphetamine was exerting its selective suppressant effect via the release of dopamine. It is suggested that the effects of low doses d-amphetamine on behaviour in conflict situations may provide a useful model for investigating the mode of action of neuroleptic drugs.

Regarding the functional equivalence of response-independent events and extinction

Rats were trained to press a lever for food according to a variable-interval (VI) 60-sec schedule of reinforcement. They were then divided into four groups and received 10 sessions of either extinction or response-independent pellets delivered according to a variable-time (VT) 30-, 60-, or 120-sec schedule. Leverpressing was reduced at approximately the same rate for subjects receiving extinction, VT 30- and VT 120-sec pellet deliveries. Relative to thse groups, the VT 60-sec group exhibited slower reductions in responding. Subjects in the three VT groups were most frequently observed to contact the food magazine, whereas, subjects in the extinction group typically faced away from the magazine and appeared to be sleeping.

MATCHING, CONTRAST, AND EQUALIZING IN THE CONCURRENT LEVER‐PRESS RESPONDING OF RATS1

Five rats pressed levers for food reinforces delivered by several concurrent variable-interval variable-interval schedules. The rate of reinforcement available for responding on one component schedule was held constant at 60 reinforcers per hour. The rate of reinforcement available for responding on the other schedule varied from 30 to 240 reinforcers per hour. The behavior of the rats resembled the behavior of pigeons pecking keys for food reinforcers. The ratio of the overall rates of responding emitted under, and the ratio of the time spent responding under, the two components of each concurrent schedule were approximately equal to the ratio of the overall rates of reinforcement obtained from the components. The overall rate of responding emitted under, and the time spent responding under, the variable component schedule varied directly with the overall rate of reinforcement from that schedule. The overall rate of responding emitted under, and the time spent responding under, the constant component schedule varied inversely with the overall rate of reinforcement obtained from the variable component. The local rates of responding emitted under, and the local rates of reinforcement obtained from, the two components did not differ consistently across subjects. But they were not exactly equal either.

Hypothalamic stimulation facilitates contralateral visual control of a learned response.

Rats that ate during hypothalamic stimulation were trained to press a lever for food only while receiving light signals from head-mounted lights. During stimulation, they pressed if the signal was visible to the eye contralateral to the electrode, but ignored the signal if it was visible only to the ipsilateral eye.

An opponent-process interpretation of postshock bursts in appetitive responding

While eight food-deprived rats pressed a lever for food during daily 1-h sessions, four CS-Shock2 trials were presented. Trials were preceded by either a Shock1 of .25, .50, .75 mA or no Shock1. It was found that the rate of appetitive responding during the CS was greater on Shock1-CS-Shock2 trials relative to CS-Shock2 trials. The data indicate that the phenomenon of postshock bursts in responding can occur in the absence of a signal for safety after shock. The results conform to the predictions of the opponent-process theory of motivation.

The Effects of Isolation Rearing on Behavioural Inhibition in the Rat

The possibility that isolation-rearing in the rat affects the development of inhibitory mechanisms was studied in a series of experiments. It was found that socially-isolated rats were (1) slower to learn both a lever-panel alternation, and a two-lever alternation schedule of reinforcement, (2) more persistent than controls in pressing a lever for food when a supply of identical “free food” was introduced into the operant chamber, but (3) similar to control rats in their response to preloading with food, a procedure which inhibited lever pressing to the same extent in the two groups. Finally, it was shown in a separate experiment that the effects of increased food deprivation on lever pressing in the presence of free food were qualitatively different from the effects of social isolation, and therefore the social/isolate difference cannot be interpreted as motivational. The possible contributions of neophobia to the difference are discussed. It is concluded that isolates may well suffer from a disinhibitory defect, but that there are probably other effects of isolation in addition.

Vulnerability of Developing Brain: Relative Effects of Growth Restriction during the Fetal and Suckling Periods on Behavior and Brain Composition of Adult Rats

Growth restriction was achieved by underfeeding mother rats during pregnancy and lactation. Offspring were either ( i ) adequately nourished during the fetal and suckling periods, (ii) undernourished during both, or (iii) and (iv) undernourished during one or the other period. All rats were fed ad libitum from weaning. The post- natally underfed animals were the most efficient at running a maze for a food reward. Differences in levels of motivation were sought using a Skinner box in which rats learned to press a lever for food. Normal rats had the lowest lever-pressing rate and those re stricted both pre- and postnatally had the highest. The tendency to inhibit movement to avoid an electric shock was weakest in normal rats and greatest in the doubly deprived animals. As in the Skinner box test, rats undernourished during only one period occu pied intermediate positions. This is taken to indicate that, with respect to these two measures of behavior, the effects of undernutrition in the fetal and suckling periods were additive. Evidence for an additive effect on physical brain growth is confined to fore- brain DNA-P content, which was substantially reduced by both periods of growth retardation. Cerebellum DNA-P and weights of cerebellum and forebrain were all much more affected by the postnatal treatment. J. Nutr. 103: 1327-1338, 1973.

Secondary reinforcement and information as determinants of observing behavior in monkeys (Macaca mulatta)

Responses on a food lever were reinforced on alternating Variable Ratio and Extinction schedules, while concurrent responses on an observing lever produced positive and negative cues correlated with the two schedules. In Experiment I the Variable Ratio requirement was reduced, thereby increasing the density of reinforcement in the presence of the positive cue but reducing average uncertainty as to the effective schedule. The result was a reduction in observing response rates. In Experiment II uncertainty was reduced through presentations of an informative light rather than primary reinforcement, and again the result was a decrease in observing behavior. In Experiment III presentations of the negative cue associated with nonreinforcement were discontinued, and omission of this presumably aversive stimulus again significantly reduced observing behavior. These results were interpreted as generally supporting an information analysis of observing behavior.

Group operant behavior in free-feeding squirrel monkeys.

Colony caged squirrel monkeys provided with ad lib. food lever pressed at high rates for Noyes pellets on CRF. 4 males had been hand shaped in individual chambers earlier but 7 females were naive; all but 2 females were observed pressing the bar on the first day.

Trial-and-error behaviour of inbred and F 1 hybrid mice

The trial-and-error behaviour of male C57 BL Tb A2 G Tb and F 1 mice was investigated in apparatus in which pressing a lever can release a pellet of food. A2 G Tb mice had the highest basic unrewarded pressing rate. C57 BL Tb mice learned to press the lever for food as readily as F 1 mice and more readily than A2 G Tb mice, despite being slowest to start pressing the lever. Response rates rose as the frequency of reward was reduced from one pellet every press to 1 : 50 presses. Hybrid mice tended to perform more efficiently than their inbred parents on the 1 : 5 and 1 : 10 schedules. The rate of pressing by A2 G Tb mice continued to increase on very low ratios of reward, but that of C57 BL Tb mice fell markedly. A2 G Tb mice tended to be the most efficient when restraint was rewarded (not pressing the lever during a delay before the arrival of the pellet), but their superiority disappeared on the longest delay. On extinction schedules, in which lever-pressing was no longer rewarded, the classes differed little. Over all, the hybrid mice were more efficient than either inbred parent strain.

Adventitious Punishment in Two Conditioned Suppression Procedures

9 male hooded rats were trained to press a lever for food on a variable interval schedule of reinforcement. They received 40 1-hr. sessions on 1 of 4 temporally defined schedules of conditioned suppression. A new procedure was then designed. Ss received 15 sessions in which electric shock occurred either at the end of programmed stimulus periods or contingent upon the first response emitted after onset of the last minute in stimulus. A significant punishment effect of contingent shock was observed ( p < .01) that was mostly due to shock closely following a whole sequence of responses. The usefulness of the behavioral baseline thus obtained for the study of psychotropic drugs is discussed.

Electrophysiological concomitants of simple operant conditioning in the rat

While rats learned to press a lever for food, both heart rate (HR) and subcortical EEGs developed significant bitonicity in the period ranging from a few seconds before to a few seconds after responses. The HR curve was an inverted-V, with the peak value located at the moment of response and falling off regularly on either side. EEGs recorded from septum, hippocampus, midbrain tegmentum, and central gray substance were electronically analyzed in a frequency band of 16–28 Hz. Bitonic EEGs, which were obtained from all placements except the motor cortex, were phased oppositely to HR (i.e. U-shaped), with the trough coinciding with the response. HR bitonicity develops earlier than EEG bitonicity, but both trends disappear very rapidly in extinction. Evidence is presented indicating that response-oriented, electrophysiological bitonicity is a neural correlate of reinforcement.

Conditioned suppression by a stimulus associated with nalorphine in morphine-dependent monkeys.

Three rhesus monkeys, physically dependent on morphine, were trained to press a lever for food on a fixed ratio of 10 responses. A tone, initially a neutral stimulus, was aperiodically presented every third or fourth session, 5 min before and after the intravenous injection of nalorphine, a morphine antagonist which produces an immediate withdrawal syndrome in morphine-dependent monkeys. After several sessions, conditioned suppression of food-lever response rate was observed. Conditioned bradycardia, emesis, and excessive salivation also occurred. In 40 to 45 sessions the conditioned suppression of food-lever response rate and the conditioned autonomic changes were extinguished by presenting pairings of a tone and saline injection. The monkeys were then reconditioned by presenting the tone aperiodically, every third or fourth session, 5 min before and after the intravenous injection of nalorphine. Results were similar to the initial conditioning sessions. Two rhesus monkeys not dependent on morphine were stabilized on a food schedule similar to that used for the first three monkeys. These monkeys showed no change in food-lever response rate during or after nalorphine injections.

Observational learning of a lever pressing response

Eighteen rats were taught to press a lever for food using either an observational technique or a shaping technique. The median number of sessions taken to learn was smaller when the observational technique was used.

Behavioural effects of a long-term treatment with meprobamate in cats

The action of meprobamate on conditioned behaviour was studied with cats. The subjects were trained to press a lever for food in a Skinner-☐ on a fixed-interval schedule of reinforcement. They develop a typical pattern of behaviour, characterized by a spontaneous temporal discrimination. Meprobamate increases the rate of responding and disrupts the temporal discrimination. These effects are similar to those obtained with chlordiazepoxide. Both effects are reduced and disappear with prolonged treatment (150 mg meprobamate daily). The tolerance extends to the general motor symptoms observed at the beggining of the treatment. When chlordiazepoxide is again administered after tolerance to meprobamate has developed, its effects on conditioned behaviour are still observed, though those on general motor behaviour are not (partial cross-tolerance). Animals treated with high doses show withdrawal reaction when the drug is no longer administered.

Action of chlordiazepoxide on two types of temporal conditioning in rats

The action of chlordiazepoxide on two kinds of behaviour involving a temporal component is studied. Rats were trained, in an operant conditioning situation to press a lever for food either on a fixed interval schedule of reinforcement or on a schedule of differential reinforcement of low rates of responding. In both cases, a temporal discrimination develops; in the first case, it is spontaneous, while it is the condition for reinforcement in the second case. Chlordiazepoxide increases the conditioned activity, as measured by the number of responses, and produces a disruption of timing behaviour. Both effects are more pronounced, and can be observed for smaller doses of the drug, under the fixed interval schedule, where the temporal discrimination is not the condition for reinforcement. Results are discussed in terms of drug behaviour interaction. The muscle relaxant action of chlordiazepoxide is hypotetically suggested as an explanation of its effects on timing behaviour.

Distinct "feeding" and "hunger motivating" systems in the lateral hypothalamus of the rat.

Electrodes were implanted in the middle hypothalamus of rats to determine the neural organization of the "feeding" centers. Stimulations of the farand midlateral hypothalamic area produced feeding responses in sated animals, but only the former caused sated animals to cross an electrified grill to press a lever for food. After lesions had been made in the medial forebrain bundle, however, stimulations in the far-lateral hypothalamic area resulted in feeding in sated animals but failure to cross the electrical barrier to press a lever for food. Simultaneous far-lateral and "satiety" center stimulations produced feeding in sated animals but failed to "motivate" grill-crossing behavior.