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At least 631 records · Page 35Linked to original sources
PubMed1988

Effects of electrical stimulation of brain reward sites on release of dopamine in rat: an in vivo electrochemical study.

Behavioral studies suggest that mesencephalic dopamine neurons mediate the rewarding effects of electrical stimulation of the medial forebrain bundle. Yet there is little direct evidence that rewarding electrical stimulation actually activates dopamine-containing neurons. The purpose of the present study was to determine, using in vivo electrochemistry, if electrical stimulation applied to lateral hypothalamic or ventral tegmental reward sites would elicit changes in extracellular levels of dopamine. In vivo high speed chronoamperometric recordings were performed in anesthetized rats that had been previously trained to respond for rewarding electrical stimulation of the medial forebrain bundle or ventral tegmental area. We found that a single 500 msec train of pulses elicited a small transient electrochemical signal, the magnitude of which was dependent on the pulse duration and frequency. This signal was potentiated by inhibition of dopamine reuptake. Prolonged electrical activation with a self-stimulation-like regimen resulted in the gradual accumulation of an electroactive compound, tentatively identified as dihydroxyphenylacetic acid (DOPAC). Taken together, the data reported here support the idea that rewarding electrical stimulation causes the release of dopamine.

Animals↗
PubMed2003

Effects of a reward downshift on the consummatory behavior and flower choices of bumblebee foragers.

Insect foragers often exhibit flower constancy, the tendency to visit single flower types rather than sample alternative flowers that provide equal or higher levels of reward. We employed a negative incentive contrast procedure to examine whether a decrease of sucrose concentration in a regularly visited flower type affects bumblebee (Bombus impatiens) consummatory or choice behavior. Subjects were trained to enter a test arena where they foraged on a single, red, artificial flower that contained 140 microl of sucrose solution. Subjects were reinforced with a concentration of either 0.50 or 0.20 sucrose solution in 20 trials and in 12 subsequent test trials subjects were given a choice between a red and yellow flower that each contained 140 microl of 0.20 sucrose solution. Subjects that experienced a downshift of reward showed an abrupt disruption in consumption of sucrose solution from the red flower. These subjects were also significantly more likely to visit the novel yellow flower than subjects that were reinforced with 0.20 sucrose solution in red flowers in all trials. However, the effects of the downshift of reward were transient and appeared to disrupt consummatory behavior more strongly than flower preferences. These results support the idea that bumblebee foragers form expectations of reward in flowers--as is implied by the results of studies of honeybees--and suggest that unrealized expectations of reward may cause foragers to sample alternative flowers or to fly considerable distances in search of particular types of flowers.

Animals↗
PubMed2000

Risk-sensitive foraging in rats: the effects of response-effort and reward-amount manipulations on choice behavior.

The literature on risk-sensitive foraging theory provides several accounts of species that fluctuate between risk-averse and risk-prone strategies. The daily energy budget rule suggests that shifts in foraging strategy are precipitated by changes in the forager's energy budget. Researchers have attempted to alter the organism's energy budget using a variety of techniques such as food deprivation, manipulation of ambient temperatures, and delays to food reward; however, response-effort manipulations have been relatively neglected. A choice preparation using a wheel-running response and rats examined risk-sensitive preferences when both response effort and reward amounts were manipulated. Concurrently available reinforcement schedules (FI/60 and VI/60) yielded equivalent food amounts per unit time in all treatments. Two levels of response effort (20 or 120 g tangential resistance) and two levels of reward amount (three or nine pellets) were combined to form four distinct response-effort/reward-amount pairings. Increasing reward amounts significantly shifted choice toward the FI schedule in both response-effort conditions. The incidence of choice preference and the magnitude of shifts in choice were greater for the high response-effort conditions than for the low response-effort conditions. Implications of the significant interaction between response effort and reward amount are discussed in terms of a general energy-budget model.

Journal Article↗
PubMed1996

Retroactive interference effects of surprising reward omission on serial spatial memory.

Reward omission was used to produce retroactive interference in a serial delayed-alternation task. Rats were given forced choices in 3 T mazes presented in succession followed by free choices in which the alternate arm in each maze was rewarded. Nonreward during the delay between forced- and free-choice runs produced a decrement in performance (i.e., retroactive interference) in comparison to reward during the delay. Interference in retention of the first maze in a list occurred when the second maze contained surprising reward or omission (i.e., an outcome contrary to previous training in that maze) in comparison to expected reward or omission. In addition to producing retroactive interference, omission sometimes increased alternation in the maze in which it occurred. These results support a differential rehearsal hypothesis of spatial memory.

Animals↗
PubMed1994

Competition and summation between rewarding effects of sucrose and lateral hypothalamic stimulation in the rat.

Rats were offered a forced choice between a train of brain stimulation that varied in strength from trial to trial and a fixed standard reward. This standard reward consisted of an intraoral sucrose infusion presented either alone or paired with an equipreferred train of brain stimulation. Postingestional effects were minimized by opening a gastric cannula. The presence of a sucrose standard led the subjects to forgo trains of brain stimulation for which they had responded when the sucrose was absent. The strength of the brain stimulation required to balance the compound reward exceeded the stimulation strength required to balance a reward consisting of sucrose alone. These results imply that the rewarding effects of brain stimulation and intraoral sucrose can be evaluated in a common system of measurement and combined.

Animals↗
PubMed1996

Destruction of the medial forebrain bundle caudal to the site of stimulation reduces rewarding efficacy but destruction rostrally does not.

Rats with an electrode in the medial forebrain bundle (MFB) in or near the ventral tegmental area and another at the level of the rostral hypothalamus sustained large electrolytic lesions at either the rostral or the caudal electrode. The rewarding efficacy of stimulation through the other electrode was determined before and after the lesion. Massive damage to the MFB in the rostral lateral hypothalamus (LH) generally had little effect on the rewarding efficacy of more caudal stimulation, whereas large lesions in the caudal MFB generally reduced the rewarding efficacy of LH stimulation by 35-60%. Similar reductions were produced by knife cuts in the caudal MFB. These results appear to be inconsistent with the hypothesis that the reward fibers consist either of descending or ascending fibers coursing in or near the MFB. It is suggested that the reward fibers are collaterals from neurons with both their somata and their behaviorally significant terminals located primarily in the midbrain.

Animals↗
PubMed2006

Amphetamine lowers brain stimulation reward (BSR) threshold in alcohol-preferring (P) and -nonpreferring (NP) rats: regulation by D-sub-1 and D-sub-2 receptors in the nucleus accumbens.

Differences in the mesolimbic dopamine (DA) pathway that regulates alcohol preference may also increase sensitivity to the reinforcing effects of other drugs of abuse. In the present study, the curve-shift (rate-frequency) paradigm was used to quantify the interaction of amphetamine with the rewarding effects of lateral hypothalamic brain stimulation reward (BSR) in alcohol-preferring (P) and -nonpreferring (NP) rats. The role of D-sub-1 and D-sub-2 DA receptors of the nucleus accumbens (NAcc) in mediating the reward-potentiating effects of amphetamine was also determined. Animals were tested with randomly administered amphetamine (0.25, 0.75, 1.25 mg/kg ip), DA-receptor antagonists (SCH 23390 [2.0 microg, 5.0 microg]; eticlopride [2.0 microg, 5.0 microg]), or a combination of the 2 (SCH 23390 [2.0 microg, 5.0 microg] + 0.75 mg/kg amphetamine; eticlopride [2.0 microg, 5.0 microg] + 0.75 mg/kg amphetamine). Amphetamine produced comparable dose-related leftward shifts in the rate-frequency function for both P and NP rats, with a greater than 60% reduction observed in BSR threshold. On intervening days, baseline threshold was unaltered between tests and similar between rat lines. Unilateral infusion in the NAcc of either the D-sub-1 or D-sub-2 receptor antagonist produced rightward shifts in the rate-frequency function of amphetamine, completely reversing-attenuating its reward-enhancing effects. The results demonstrate that amphetamine produces similar threshold-lowering effects in both P and NP rats and that the reward-potentiating effects of amphetamine do not correlate with alcohol preference under the conditions of the present study.

Alcohol Drinking↗
PubMed2004

A longitudinal study comparing the effort-reward imbalance and demand-control models using objective measures of physician utilization.

BACKGROUND: The objectives of this study were to compare the predictive validity of the demand-control and effort-reward imbalance models using objective measures of physician utilization. METHODS: Self-reports for psychosocial work conditions were obtained in interviews with 1,028 workers using the demand-control and effort-reward imbalance models. Physician utilization outcomes were obtained through linkage to the British Columbia Linked Health Database. Outcomes were any visit to a physician for mental health reasons and 30 or more physician visits for any reason. The predictive validity of both models was compared in a longitudinal study using logistic regression. RESULTS: Neither job strain nor effort-reward imbalance predicted either outcome. However, low esteem reward and low status control increased the risk for 30 or more physician visits by, respectively, approximately 60% and 30%. CONCLUSIONS: In a sample of middle-aged blue-collar current and ex-sawmill workers in Western Canada, followed prospectively, after controlling for sociodemographic and workplace confounders, and reducing the potential for adverse health selection into high-stress jobs, low esteem reward and low status control were associated with a significantly greater risk for 30 or more physician visits for any reason.

Adult↗
PubMed2004

Transient inactivation of the rat nucleus accumbens does not impair guidance of instrumental behaviour by stimuli predicting reward magnitude.

The involvement of the nucleus accumbens (NAc) in the determination of reaction times (RTs) of instrumental responses by the expectancy of future reward was investigated. A simple RT task demanding conditioned lever release was used, in which the upcoming reward magnitude (5 versus 1 pellet) was signalled in advance by discriminative cues. In rats which acquired the task, RTs of instrumental responses were significantly shorter to the discriminative cue predictive of high reward magnitude. Inactivation of the NAc by lidocaine had no effect on RTs and their determination by cue-associated reward magnitudes, and did not affect the rate of correct responses. In keeping with an earlier study, intra-NAc infusion of amphetamine decreased RTs, impaired RT determination by cue-associated reward magnitudes and reduced the rate of correct responses. The unexpected finding that lidocaine inactivation of the NAc had no effect parallels previous data showing that lesions of NAc did not impair RT performance, while manipulation of intra-NAc glutamate or dopamine transmission impaired various aspects of RT performance in comparable tasks. It is suggested that experimental manipulations such as transient and permanent inactivation, which almost completely inhibit NAc neuronal output, allow alternative routes to be used to effectively control behaviour in the task employed here.

Animals↗
PubMed2006

Individual differences in decision making: Drive and Reward Responsiveness affect strategic bargaining in economic games.

BACKGROUND: In the growing body of literature on economic decision making, the main focus has typically been on explaining aggregate behavior, with little interest in individual differences despite considerable between-subject variability in decision responses. In this study, we were interested in asking to what degree individual differences in fundamental psychological processes can mediate economic decision-making behavior. METHODS: Specifically, we studied a personality dimension that may influence economic decision-making, the Behavioral Activation System, (BAS) which is composed of three components: Reward Responsiveness, Drive, and Fun Seeking. In order to assess economic decision making, we utilized two commonly-used tasks, the Ultimatum Game and Dictator Game. Individual differences in BAS were measured by completion of the BIS/BAS Scales, and correlations between the BAS scales and monetary offers made in the two tasks were computed. RESULTS: We found that higher scores on BAS Drive and on BAS Reward Responsiveness were associated with a pattern of higher offers on the Ultimatum Game, lower offers on the Dictator Game, and a correspondingly larger discrepancy between Ultimatum Game and Dictator Game offers. CONCLUSION: These findings are consistent with an interpretation that high scores on Drive and Reward Responsiveness are associated with a strategy that first seeks to maximize the likelihood of reward, and then to maximize the amount of reward. More generally, these results suggest that there are additional factors other than empathy, fairness and selfishness that contribute to strategic decision-making.

Journal Article↗
PubMed1994

Synergistic effects of ethanol and cocaine on brain stimulation reward.

The effects of two widely abused drugs, ethanol and cocaine, were examined alone and in combination on intracranial reward processes. In agreement with previous research, higher doses of both cocaine and ethanol alone produced facilitation of behavior maintained by brain stimulation reward. Low intraperitoneal doses of ethanol and cocaine, which alone did not affect performance, were found to reduce stimulation reward threshold and modestly increase response rate. The enhancement of brain stimulation reward by the combination of ethanol and cocaine suggests that both drugs may produce their rewarding effects through common neuronal substrates and that they may potentiate the abuse of each other.

Animals↗
PubMed2003

Building blocks of self-control: increased tolerance for delay with bundled rewards.

Impulsive choice can be defined as temporary preference for a smaller-sooner reward (SS) over a larger-later reward (LL). Hyperbolic discounting implies that impulsive choices will occur less when organisms choose between a series of SSs versus LLs all at once than when they choose between single SS versus LL pairs. Eight rats were exposed to two conditions of an intertemporal choice paradigm using sucrose solution as reward. In both conditions, the LL was 150 microl delayed by 3 s, while the SS was an immediate reward that ranged from 25-150 microl across sessions. Preference for the LL was greater when the chosen reward was automatically delivered three times in succession (bundled) than when it was chosen singly and delivered after each choice. For each of the 8 rats, the estimated SS amount that produced indifference was higher in the bundled condition than in the single condition. Because bundling in humans may be based on the perception that one's current choice is predictive of future choices, the data presented here may demonstrate an important building block of self-control.

Animals↗
PubMed1995

Dopamine D1-like receptor agonists impair responding for conditioned reward in rats.

The dopamine (DA) D1-like receptor agonist SKF 38393 has been reported to impair responding for conditioned reward. SKF 38393 is a partial agonist and it is possible that the impairment occurred because it prevented endogenous DA from having its full impact on the D1-like receptor. The present experiments evaluated this possibility by examining the effects of several D1-like agonists with differing efficacy at stimulating adenylate cyclase. Male rats (n = 203) were trained in a procedure with three distinct phases. During the pre-exposure phase the rats were exposed for five 40min sessions to an operant chamber containing two levers; one produced a lights-off and the other a tone stimulus (3s). This was followed by the conditioning phase, four sessions during which the levers were removed and the rats received pairings of the lights-off stimulus (80 per day) with food, presented according to a variable time 45s schedule. The test phase included two sessions during which the levers were present and the number of responses made on each lever was calculated as a ratio of the number of responses made during pre-exposure. Drugs were administered prior to each test session. No-injection and saline groups showed a higher ratio of responding for the lights-off than the tone stimulus, indicating that the lights-off stimulus had become a conditioned reward. The full D1-like agonist SKF 82958 (0.01-1.0mg/kg, s.c.) and the partial agonists SKF 81297 (0.01-1.0mg/kg), SKF 77434 (0.01-5.0mg/kg) and CY 208-243 (0.01-1.0mg/kg) impaired responding for conditioned reward at one or more of the highest doses. Results suggest that the impairments previously seen with SKF 38393 are not attributable to the partial agonist action of that drug, and continue to support the hypothesis that responding for conditioned reward is dependent on a reward-related DA signal at the D1-like receptor.

Journal Article↗
PubMed1999

Extinction after regular and irregular reward schedules in the infant rat: influence of age and training duration.

Greater persistence in extinction is observed following inconsistent reward compared to that observed following consistent reward, an effect termed the partial reinforcement extinction effect (PREE). We report three experiments in which the extinction rates of random partially reinforced (PRF) or continuously reinforced (CRF) infant rat pups were compared to the extinction rate of pups trained with an alternative and regular schedule of partial reinforcement, known as patterned single alternation (PSA). In PSA, subjects learn to alternate speed of responding in anticipation of the regular alternation of reward and nonreward trials in the straight alley runway. In Experiment 1, 17-day-old PSA subjects showed CRF-like extinction rates; whereas in Experiment 2, in which extinction was initiated early in training prior to the onset of the PSA discrimination, PSA subjects showed prolonged, PRF-like extinction curves. In contrast, 12-day-old pups in Experiment 3 showed no reward-schedule-related differences in extinction, despite differences in behavior during acquisition. These results prompt a modification of Amsel's (1962) model of discrimination learning, and suggest the existence of a dissociation between different types of reward-related expectancies in the younger subjects.

Age Factors↗
PubMed2005

Functional neuroanatomical substrates of altered reward processing in major depressive disorder revealed by a dopaminergic probe.

CONTEXT: The pathophysiology of major depressive disorder (MDD) includes disturbances in several neuroanatomical substrates and neurotransmitter systems. The challenge is to elucidate the brain mechanisms of MDD behavioral symptoms, chiefly those of anhedonia. OBJECTIVES: To visualize the neuroanatomical substrates implicated in altered reward processing in MDD, using functional magnetic resonance imaging in combination with a dopaminergic probe (a 30-mg dose of oral dextroamphetamine sulfate) to stimulate the brain reward system; and to test the hypothesis that a hypersensitive response to dextroamphetamine in MDD involves the prefrontal cortex and the striatum. DESIGN AND INTERVENTIONS: Among subjects with MDD and healthy control subjects, functional magnetic resonance imaging data were collected before and after single-blind administration of dextroamphetamine. SETTING: Subjects were recruited through local newspaper advertisements and by word of mouth. PARTICIPANTS: Twelve depressed subjects (mean age, 34.83 years; male-female ratio, 6:6) met criteria for MDD according to the DSM-IV, were not taking antidepressants, and had no comorbid Axis I disorders. Twelve control subjects (mean age, 29.33 years; male-female ratio, 5:7) were healthy volunteers without a history of Axis I disorders. MAIN OUTCOME MEASURES: Functional magnetic resonance imaging blood oxygen level-dependent activation was measured during a controlled task, and dextroamphetamine-induced subjective effects were assessed using the Addiction Research Center Inventory. RESULTS: Subjects with MDD had a hypersensitive response to the rewarding effects of dextroamphetamine (2-fold increase; t(21) = 2.74, P = .01), with altered brain activation in the ventrolateral prefrontal cortex and the orbitofrontal cortex and the caudate and putamen (F(1,44) = 11.93, P = .001). CONCLUSION: Dopamine-related neuroanatomical substrates are involved in altered reward processing in MDD, shedding light on the neurobiology of the anhedonic symptoms in MDD and suggesting these substrates as future therapeutic targets.

Adult↗
PubMed2007

Separate brain regions code for salience vs. valence during reward prediction in humans.

Predicting rewards and avoiding aversive conditions is essential for survival. Recent studies using computational models of reward prediction implicate the ventral striatum in appetitive rewards. Whether the same system mediates an organism's response to aversive conditions is unclear. We examined the question using fMRI blood oxygen level-dependent measurements while healthy volunteers were conditioned using appetitive and aversive stimuli. The temporal difference learning algorithm was used to estimate reward prediction error. Activations in the ventral striatum were robustly correlated with prediction error, regardless of the valence of the stimuli, suggesting that the ventral striatum processes salience prediction error. In contrast, the orbitofrontal cortex and anterior insula coded for the differential valence of appetitive/aversive stimuli. Given its location at the interface of limbic and motor regions, the ventral striatum may be critical in learning about motivationally salient stimuli, regardless of valence, and using that information to bias selection of actions.

Adult↗
PubMed2005

Hippocampal theta activity and behavioral sequences in a reward-directed approach locomotor task.

Hippocampal rhythmic slow wave activity (theta) has been implicated in the processing of stimuli associated with movement. This study determined whether the theta rhythm showed phase relationships or changes in amplitude and frequency with the onset of stimuli and behavioral sequences in a skilled locomotor approach task. Rats with bipolar electrodes spanning CA1 approached a stall, turned to enter it, approached and depressed a treadle, waited 1.35 s, and approached a milk reward located forward either to the right or to the left. Auditory cues indicated the location of the reward during the waiting period and at the reward onset. A video capture system (20-ms sampling) was synchronized to the hippocampal recording system (10-ms sampling). Behavioral events identified by motion analysis were used to generate averages of hippocampal slow wave activity, theta peak amplitudes, and intervals between peaks. Theta activity at 8-10 Hz was almost continuous during the behavioral sequences. Phase relations with stimuli or movement onsets occurred infrequently and were not consistent across the four subjects. Theta peak amplitude and frequency decreased as the rat slowed locomotion in the stall and reached the treadle. Onset of locomotion directed to a reward location occurred on a positive peak of averaged theta activity. When locomotion had short latencies, increases in theta frequency appeared after the onset but, when it had longer latencies, frequency increases appeared 200 ms before onset. The results indicate that the execution of instrumental movement modulates both theta amplitude and frequency, and that the preparation for locomotion modulates theta frequency.

Action Potentials↗
PubMed2005

Tiagabine reduces ethanol reward in C57BL/6 mice under acute and chronic administration regimens.

Three experiments conducted on male C57BL/6 (B6) mice examined the effects of subcutaneous injections of the GABA uptake inhibitor, tiagabine, on appetitive (lever responding) and consummatory behavior (fountain contacts) of food restricted B6 mice for 12% ethanol and water rewards (Exp-1), and for food reward (Exp-2) delivered on a fixed ratio 4 schedule of reinforcement. Effects of acute injections (1,3,6,9 mgkg) and chronic administration (6,9 mg/kg) was examined. Exp-3 examined tiagabine effects on the voluntary consumption of continuously available 12% ethanol, and on the interactive effects of tiagabine and ethanol on motor activity of non-food restricted B6 mice. Results of Exp-1 and Exp-2 indicated that tiagabine can reduce appetitive behavior for ethanol reward with no evidence of tolerance upon chronic exposure. Tiagabine doses that reduced ethanol reward had less effect on behavior maintained by either water or food, and had no effect on motor activity. In contrast to the absence of tolerance to its effect on appetitive behavior for ethanol, mice rapidly developed tolerance to tiagabine's initial reduction of the consummatory response for ethanol (Exp-1), and the intake of freely available ethanol exceeded pre-tiagabine levels after several daily injections (Exp-3). Importantly, mice developed tolerance to tiagabine's sedative effect after three daily injections and its sedation was not enhanced when combined with ethanol, an effect consistent with the lack of a tiagabine + ethanol interaction previously reported for humans. The results of the experiments suggest that in addition to reducing alcohol withdrawal symptoms, tiagabine might also reduce the potency of ethanol-conditioned cues that drive appetitive behavior for ethanol.

Alcohol Drinking↗