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PubMed1996

Conditioned whisking in the rat.

The rat's mystacial vibrissae are active during exploratory and discriminative behaviors, with individual vibrissae serving as elements in a receptive array scanned across object surfaces. To facilitate neurobehavioral analysis of this sensorimotor system, we have developed an experimental paradigm that confines vibrissa movements to a defined physical location, makes possible on-line monitoring of "whisking" activity, and brings such activity under associative control using operant conditioning procedures. Rats were secured, and movements of an identified bilaterally homologous pair of vibrissae (right and left gamma straddlers) were detected by laser-based photodetectors. Subjects were maintained on a water deprivation schedule, and whisker movements were monitored during adaptation to the test situation and after the clipping of other vibrissae on both sides of the snout. Rats were reinforced with water delivery for emitting vibrissa movements in the presence of a conditioned stimulus (tone) whose presentation was made contingent upon a prior period of nonwhisking. The rate and temporal distribution of vibrissa movements were brought under experimental control by means of interval and ratio reinforcement schedules. Although the procedures provide minimal information about the kinematics or topography of conditioned vibrissa movements, they permit the investigator to manipulate response parameters normally under the voluntary control of the animal in a preparation amenable to neurophysiological analysis.

Animals↗
PubMed1967

Attention and temporal discrimination: factors controlling responding under a cyclic-interval schedule.

Pigeons were exposed to a cyclic schedule in which each cycle was composed of twelve 1-min fixed intervals followed by four 3-min fixed intervals; four such cycles comprised an experimental session. The pigeons responded at a much higher average rate during the 3-min intervals than during the 1-min intervals. Other effects were a depression of responding during the first short interval of each cycle and a shortening of postreinforcement pause during the second short interval. The main effect is attributable to a relatively fixed pattern of responding after reinforcement; this pattern consisted in a pause of approximately constant duration followed by responding at an approximately constant rate until the next reinforcement, resulting in much higher average response rates during the longer interreinforcement intervals. The other effects seem attributable to relatively slight differences between the pattern of responding characteristic of later long intervals and the pattern during later short intervals of each cycle. A major implication is that the pigeon is largely insensitive to the sequential properties of many interval-reinforcement schedules. A description of interval-schedule "frustration" phenomena in terms of the inhibitory effects of reinforcement is discussed in relation to these results.

Animals↗
PubMed1992

Choice between delayed reinforcers in an adjusting-delay schedule: the effects of absolute reinforcer size and deprivation level.

Choice between two reinforcers differing in magnitude and delay was investigated in rats using an adjusting-delay discrete-trials schedule in which the two reinforcers were associated with two levers (A and B). The delay to Reinforcer A (the smaller reinforcer) was always 2 sec, whereas the delay to Reinforcer B was varied in accordance with the distribution of choices in successive blocks of trials. In Experiment 1, the mean delay to the large reinforcer during the last 5 of 60 training sessions was greater when the rats were maintained at 80% than when they were maintained at 90% of their free-feeding body weights. In Experiment 2, the delay to the larger reinforcer was greater when the two reinforcers consisted of one and two 45-mg food pellets than when they consisted of three and six pellets. The results are consistent with a model of "self-control" which posits hyperbolic relations between reinforcer value and reinforcer magnitude, and between reinforcer value and delay of reinforcement.

Animals↗
PubMed1996

NMDA-induced lesions of the nucleus accumbens or the ventral pallidum increase the rewarding efficacy of food to deprived rats.

The role of the nucleus accumbens (NAC) and ventral pallidum (VP) in food reward modulation was investigated using Heyman's [24] curve fitting approach in food deprived rats. All rats were maintained at 80% normal body weight, and trained to lever press for food reinforcement. Each rat was tested daily with a series of four variable-interval (VI) reinforcement schedules (80, 40, 20, and 10 s) designed to approximate an exponential distribution, and randomly administered in ascending or descending order. The maximum response rate (Rmax) and the reinforcement rate required to maintain half-maximal responding (Re50) were recorded for each rat's daily test session. Following the establishment of baseline responding, the excitotoxin N-methyl-D-aspartic acid (NMDA) was bilaterally administered into the NAC (30 micrograms per side) or VP (20 micrograms per side) over a 10 min period. Both groups displayed substantial damage to the intended structure, with the lateral regions typically sustaining more damage than medial regions, and minor damage to surrounding areas. When tested at three weeks post-lesion, a suppression of motor activity was evident in all animals when compared to pre-lesion baseline. Moreover, in almost all rats, Re50 decreased, suggesting that the rewarding efficacy of food had increased. These data are surprising, given the extensive literature on the relationship between damage in the NAC and loss of reward efficacy. However, based on pharmacological and anatomical findings, both brain regions have been divided into several subregions. Behavioral studies suggest that these subregions may differentially regulate reward and motor functions. The results from the present study suggest that (1) both the NAC and VP are involved in the modulation of food reward, (2) that lateral subregions in each structure may function to dampen food reward efficacy, and (3) that medial subregions may enhance food reward.

Animal Feed↗
PubMed2000

A cautionary note regarding drug and brain lesion studies that use swimming pool tasks: partial reinforcement impairs acquisition of place learning in a swimming pool but not on dry land.

Spatial tasks are used widely in neurobiological studies because it is thought that they provide an unbiased assessment of the integrity of neural structures that mediate spatial learning. For example, in the Morris swimming pool place task, animals are required to locate a hidden platform in a swimming pool in relation to environmental cues. Treatments that result in an animal's failure to find the platform are assumed to reflect defects in the function of neural systems involved in spatial learning. The present study demonstrates, however, that an animal's reinforcement history can contribute to its spatial performance. Animals were trained in the Morris place task with the platform present on 100, 75 or 50% of trials. Relative to the 100% group, the 75% group was impaired in place acquisition, and the 50% group failed to learn. Even placing the 50% group animals onto the platform at the completion of an unsuccessful trial failed to improve acquisition. Animals trained to search for food on an identical dry maze problem were not affected by similar reinforcement schedules. The present findings demonstrate that the Morris swimming pool place task does not provide an unbiased assessment of spatial learning: A treatment effect may be confounded with reinforcement history. The results are discussed in relation to widespread applications of the Morris place task to neurobiological problems.

Analysis of Variance↗
PubMed1979

Chained schedules of avoidance: Reinforcement within and by avoidance situations.

Four rats were exposed to chained schedules with variable-cycle avoidance in both links. Responding in the initial link cancelled shocks scheduled once per minute and, according to a conjoint fixed-ratio schedule, produced a terminal link where scheduled shock rates varied from 0 to 8 shocks per minute in different conditions of the experiment. Response rates in the terminal link increased as a function of the scheduled shock rate. Response rates in the initial link, on the other hand, decreased as a function of the shock rate actually received (rather than scheduled) in the terminal link. While consistent with other studies of aversive control, these results differ from those obtained in chained schedules of positive reinforcement in that increases in reinforcement within the terminal link of the chain did not systematically increase the reinforcing value of that link.

Journal Article↗
PubMed1998

Behavioral effects of nicotine, amphetamine and cocaine under a fixed-interval schedule of food reinforcement in rats chronically exposed to caffeine.

Epidemiological surveys demonstrate that caffeine, the main psychoactive ingredient of coffee, is a positive correlate in drug abuse. To characterize the behavioral nature of caffeine interactions with other psychomotor stimulants, we examined the effects of chronic caffeine exposure on the behavioral responses to nicotine, amphetamine, cocaine, the selective D1 agonist SKF-82958 and the selective D2 receptor agonist NPA, in rats responding under a fixed interval (FI) schedule of food reinforcement. Following stabilization of rates and temporal patterns of responding (mathematically expressed as quarter-life values, QL), twenty-one Sprague-Dawley rats responding under a 5-min FI schedule of food reinforcement were divided into two groups; one (twelve rats) maintained on tap water (control) and the other (nine rats) on caffeine (3 mg/ml added to the drinking water). Following the substitution of caffeine solution for tap water, behavior was temporarily disrupted as evidenced by decreases in responding and QL values which reached a maximum after 72 h (rate 60% and QL 30% below baseline levels). Rats developed complete tolerance to these effects of caffeine over 5 days of caffeine exposure. After response rate and QL values stabilized, effects of drugs were evaluated. Nicotine (0.01-1.0 mg/kg; SC), amphetamine (0.1-5.6; IP), and cocaine (1.0-17; IP) each produced biphasic dose-dependent changes in response rate with maximum increases in response rate following intermediate doses and decreases in response rates following higher doses. The increase in rates of responding produced by amphetamine or cocaine (but not nicotine) were greater (P<0.05) in caffeine-drinking than in water-drinking rats. Both SKF-82958 (0.001-0.3 mg/kg; IP) and NPA (0.0001-0.1; IP) produced only dose-dependent decreases in rates of responding. Caffeine-drinking rats were less sensitive to the rate-depressant effects of SKF-82958 (P<0.05) than water-drinking rats. However, similar changes (P>0.05) were produced by NPA in both groups. Except for amphetamine, the remaining drugs produced similar (P>0.05) dose-dependent decreases in QL values in water- and caffeine-drinking rats. Amphetamine produced smaller decreases in QL values in caffeine-drinking rats than in water-drinking rats (P<0.05). Chronic exposure to caffeine produced complete insurmountable tolerance to the response-rate increasing (stimulant) effects of acute caffeine (3.0-17 mg/kg; IP) in caffeine-drinking rats. In conclusion, our study revealed that chronic caffeine exposure potentiates the behavioral response to amphetamine and cocaine but not to that of nicotine in rats responding under a FI schedule of food reinforcement. Thus, it is likely that these effects are mediated through different pharmacological mechanisms.

Amphetamine↗
PubMed1970

Observational learning in monkeys.

Observer monkeys were housed next to demonstrator monkeys that were conditioned to respond on a multiple reinforcement schedule whose components were fixed-ratio 32, variable-interval 3-min, and extinction 5-min followed by an additional 30 sec of extinction during which every response started a new 30-sec interval. After observational periods from 113 to 210 hr long, during which observers could not perform the response and were given no extrinsic reinforcers, their first-response latencies to fixed ratio and variable interval were as short as the demonstrators; and their rates of responding were well above pre-observational baseline levels. About 8 hr later, a temporal pattern of responding appropriate to the multiple schedule emerged, including non-emission of responses during extinction. Controls lacking the chance to observe did not develop typically patterned responding after 60 hr in one case and, in two other cases, after 80 hr during which, on two occasions, every one of 50 responses was reinforced. In a second experiment, the stimulus lights associated with fixed ratio and variable interval were presented simultaneously. Subjects chose one of the schedules by responding to one of the levers beneath the lights. All subjects initially chose fixed ratio. Seeing the demonstrators switch to variable interval, due to increases in the fixed-ratio requirement, had no effect upon observers, which continued to choose fixed ratio.

Journal Article↗
PubMed1986

The curve-shift paradigm in self-stimulation.

Eleven rats were trained to press a lever in an operant chamber in order to earn rewarding trains of cathodal rectangular pulses of fixed intensity and variable frequency. The rate-frequency functions were examined under administration of two neuroleptics (pimozide and chlorpromazine) and three manipulations that interfered with bar pressing (muscular relaxation with methocarbamol, increased lever weight, and limitation of maximum response rates by an F1 reinforcement schedule). Chlorpromazine, and pimozide at low dosages produced a near parallel shift of the rate-frequency functions on the logarithmic axis of pulses, suggesting that these drugs decreased the reinforcing efficacy of the stimulation. The three conditions that interfered with bar-pressing decreased the asymptotic rates and produced small or moderate lateral shifts. Changes in the reinforcing efficacy of the stimulation following the above manipulations were inferred from the shift in the number of pulses required at zero and half-maximal performance (theta 0 and M50 indices, respectively). In the cases of the manipulations that interfered with bar-pressing, M50 indicated a larger artifactual change in the efficacy of the stimulation, compared to theta 0. This phenomenon was mainly due to the fact that the asymptote of the altered functions was shifted towards higher pulse numbers.

Animals↗
PubMed1979

Food deprivation increases oral and intravenous drug intake in rats.

Rats given continuous access to etonitazene hydrochloride in their drinking water (5 micrograms per milliliter) more than doubled their drug intake while deprived of food. Another group of rats with implanted jugular catheters self-administered etonitazene (10 micrograms per kilogram) intravenously on a continuous reinforcement schedule, and the number of infusions increased significantly on days when they were deprived of food. These results suggest that feeding condition may be a powerful determinant of drug-reinforced behavior.

Administration, Oral↗
PubMed1980

Recall (versus recognition) of taste and immunization against aversive taste anticipations based on illness.

Two experiments show that, after taste-aversion conditioning, rats can use external retrieval cues to recall or anticipate the aversive taste solution and avoid its location without making contact with the flavor. They also show that the rat's avoidance of a conditioned aversive taste and its consumption of the aversive flavored solution can be attenuated by giving it prior runway training in which taste reward is given inconsistently on a partial reinforcement schedule.

Animals↗
PubMed1995

Oral self-administration of etonitazene in rhesus monkeys: use of a fading procedure to establish etonitazene as a reinforcer.

The establishment of orally delivered etonitazene (a potent opioid) as a reinforcer, was studied in eight rhesus monkeys. Initially, when given concurrent access to 2.5 micrograms/ml etonitazene and the water vehicle, five of the monkeys rejected the drug, whereas the other three monkeys consumed more drug solution than water. The five monkeys that rejected the drug solution underwent an acquisition phase to establish the drug as a reinforcer. A fading procedure was used to transfer control of responding from a 2% (wt/vol) ethanol solution to a 2.5 micrograms/ml etonitazene solution. Initially, responding was maintained by contingent deliveries of 2% ethanol. Next, across blocks of six or more sessions, increasing amounts of etonitazene were added in steps to the 2% ethanol solution. Subsequently, the 2% ethanol solution was decreased in steps to zero, leaving only the 2.5 micrograms/ml etonitazene present. When the fading procedure was completed, dose of etonitazene was varied by increasing the volume delivered, first under fixed ratio (FR 4) and then under an FR 8 reinforcement schedule. The same dose manipulations were made with the three monkeys who did not undergo the fading procedure because they preferred etonitazene over water when first tested. Etonitazene was established as a reinforcer for six of the eight monkeys because drug deliveries exceeded vehicle deliveries across a range of drug doses.

Administration, Oral↗
PubMed1994

Behavioral effects of enantiomers of dizocilpine under two "counting" procedures in rats.

Stereoisomers of the N-methyl-D-aspartate antagonist dizocilpine (MK-801) were studied to determine whether behavioral effects on complex operants depend on reinforcement loss accompanying behavioral disruption. Rats earned food pellets if the run of consecutive left-lever presses preceding a trial-terminating right-lever press approximated a target of 12. A percentile schedule reinforced any run closer to the target than two-thirds of the runs on the most recent 24 trials. Once the sequence was learned, half the subjects were shifted to a procedure that yoked reinforcement for each length run to the probability that length generated pellets during asymptototic percentile performance. Although these two procedures generate similar control run and reinforcement distributions, disrupting behavior reduced reinforcement probability far more under the yoked than the percentile procedure. Despite this difference in drug-induced reinforcement loss, both enantiomers produced similar dose-related decreases in run length and response rate under both procedures, with the (-) isomer approximately one log unit less potent than the (+) isomer. The absence of differential effects under these procedures diminishes the likelihood that reinforcement loss contributes to dizocilpine's effects, indirectly bolstering claims that dizocilpine directly affects learning.

Animals↗
PubMedDate not supplied

Ethanol self-administration in ALKO rats: I. Effects of selection and concentration.

The ALKO Alcohol Accepting (AA) rats and Alcohol Non-Accepting (ANA) rats were used to study the relationship between ethanol preference in a two-bottle choice paradigm and oral ethanol self-administration in an operant conditioning paradigm. Ethanol served as a positive reinforcer in the preferring AA line. Under a continuous reinforcement schedule (FR 1), ethanol deliveries were consistently greater than water (vehicle) deliveries and varied as an orderly inverted U-shaped function of ethanol concentration. Conversely, in nonpreferring ANA animals, ethanol did not serve as a reinforcer. Findings obtained with the AA rats were compared with those obtained with Sprague-Dawley rats. Sprague-Dawley rats maintained higher levels of responding and greater ethanol intake, relative to AA rats, at all concentrations of ethanol tested. The data are consistent with evidence that genotype is a critical factor in determining the extent to which ethanol serves as a reinforcer. The results also suggest that ethanol preference and the maintenance of ethanol reinforced behavior under operant conditions appear to have some common mechanisms. However, since the selection for ethanol preference in AA rats apparently did not maximize the maintenance of ethanol-reinforced behavior in an operant paradigm, ethanol drinking behavior in the preference paradigm may not be completely generalizable to that observed in the operant model.

Animals↗
PubMed1992

Brain-stimulation reward: a model for the study of the rewarding effects of abused drugs.

The robustness of the findings of the BSR effects of abused substances indicates that almost any technique used to measure these effects will be useful. The simplest procedure, however, of selecting a single intensity of stimulation and determining the effects of drugs on the rate of response for that selected intensity is fraught with difficulty in interpretation. More than 25 years ago the interpretation of changes in response rate as a reflection of changes in the reward value of the stimulation was challenged (Hodos and Valenstein 1962). Today it is rare to see a single stimulation intensity used in a published manuscript. However, most studies still use procedures of which rate of response is an integral part. Because animals will press a lever more than 80 times per minute and--on a continuous reinforcement schedule--receive as many as 80 stimulations a minute, conclusions about the specificity of the effects of drugs are difficult. The results of BSR experiments on mechanisms of action of abused substances clearly indicate that the reinforcing effect of most, if not all, such substances is probably the result of activation of a reward system that originates in the cell bodies of the ventral tegmental area and courses rostrally to the limbic and frontal projection sites of the mesocortical system. Thus, we believe, the technique has clearly fulfilled its promise as a "window on the brain" (Olds 1977).

Animals↗
PubMedDate not supplied

Periadolescent alcohol alters adult behavioral characteristics in the rat.

Long-Evans hooded rats were given 5% alcohol (EtOH), 10% EtOH or tap water as sole fluid from postnatal day 21 (P21) to P70. The 10% EtOH group drank 26% less and 10% EtOH males gained 7.6% less weight than the tap water control group. There were no significant consumption or weight differences between 5% EtOH and control subjects. At P105, 35 days after the conclusion of alcohol dosing, we conducted several behavioral tests. Males in the 10% group drank 67.8% more alcohol than controls in a two-bottle preference test. On a DRL-20-s operant reinforcement schedule, a difficult timing task dependent upon limbic structures, subjects in the 10% group had higher barpress rates, while those in the 5% group had lower barpress rates than controls. On this task, 10% females received fewer reinforcements, while both 5% and 10% males earned more reinforcements than controls. Efficiency ratios were lowest for 10% females and highest for 5% males. Males in the 5% group had shorter latencies than controls to find the platform in a Morris water maze and were significantly more likely than controls to initially find the platform. These data suggest that EtOH consumption during periadolescent development may have long-lasting neurobehavioral effects.

Age Factors↗
PubMed1999

EMG reactivity and oral habits among facial pain patients in a scheduled-waiting competitive task.

For individuals with temporomandibular disorder (TMD) it has been theorized that stressful events trigger oral habits (e.g., teeth grinding), thereby increasing masticatory muscle tension and subsequent pain. Recent research involving adjunctive behaviors found an increase in masseter surface EMG (sEMG) and oral habits when students with TMD symptomatology were placed on a fixed-time reinforcement schedule. The current study used a treatment-seeking community sample with TMD symptomatology in a competitive task designed to be a more naturalistic Fixed Time task. The experiment consisted of Adaptation, Free-Play, Scheduled-Play, and Recovery phases. During the Scheduled-Play phase participants played, and waited to play, an electronic poker game. Results indicated that masseter muscle tension in the Scheduled-Play phase was significantly higher (p < .001) than in any other phase. Moreover, during the Scheduled-Play phase masseter sEMG was higher (p < .001) when participants waited to play. Self-reported oral habits and overall affect were significantly higher (p's < .05) in the Free-Play and Scheduled-Play phases relative to Adaptation and Recovery. The observation that masseter sEMG was elevated during the Scheduled-Play phase relative to all other phases, and within the Scheduled-Play phase sEMG was highest while waiting, suggests that adjunctive oral habits may lead to TMD symptomatology.

Affect↗
PubMed1996

Signaled Delay of Reinforcement: Effects of Postconditioning Manipulation of Context Associative Strength on Instrumental Performance

Two experiments examined the influence of postconditioning treatments of contextual cues on instrumental responding acquired with a signaled delay of reinforcement schedule. In Experiment 1, mere exposure to the conditioning context after instrumental training resulted in an attenuated response rate during an extinction test. In the second experiment, responding was decreased by exposure to the contextual cues or sessions in which signaled noncontingent reinforcements occurred. The greatest response decrement, however, occurred following unsignaled noncontingent food presentations. The results are discussed with respect to the different roles of contextual cues on operant responding.

Journal Article↗