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PubMed2005

Effects of lesions of the nucleus accumbens core on choice between small certain rewards and large uncertain rewards in rats.

BACKGROUND: Animals must frequently make choices between alternative courses of action, seeking to maximize the benefit obtained. They must therefore evaluate the magnitude and the likelihood of the available outcomes. Little is known of the neural basis of this process, or what might predispose individuals to be overly conservative or to take risks excessively (avoiding or preferring uncertainty, respectively). The nucleus accumbens core (AcbC) is known to contribute to rats' ability to choose large, delayed rewards over small, immediate rewards; AcbC lesions cause impulsive choice and an impairment in learning with delayed reinforcement. However, it is not known how the AcbC contributes to choice involving probabilistic reinforcement, such as between a large, uncertain reward and a small, certain reward. We examined the effects of excitotoxic lesions of the AcbC on probabilistic choice in rats. RESULTS: Rats chose between a single food pellet delivered with certainty (p = 1) and four food pellets delivered with varying degrees of uncertainty (p = 1, 0.5, 0.25, 0.125, and 0.0625) in a discrete-trial task, with the large-reinforcer probability decreasing or increasing across the session. Subjects were trained on this task and then received excitotoxic or sham lesions of the AcbC before being retested. After a transient period during which AcbC-lesioned rats exhibited relative indifference between the two alternatives compared to controls, AcbC-lesioned rats came to exhibit risk-averse choice, choosing the large reinforcer less often than controls when it was uncertain, to the extent that they obtained less food as a result. Rats behaved as if indifferent between a single certain pellet and four pellets at p = 0.32 (sham-operated) or at p = 0.70 (AcbC-lesioned) by the end of testing. When the probabilities did not vary across the session, AcbC-lesioned rats and controls strongly preferred the large reinforcer when it was certain, and strongly preferred the small reinforcer when the large reinforcer was very unlikely (p = 0.0625), with no differences between AcbC-lesioned and sham-operated groups. CONCLUSION: These results support the view that the AcbC contributes to action selection by promoting the choice of uncertain, as well as delayed, reinforcement.

Animals↗
PubMed1985

Forebrain origins and terminations of the medial forebrain bundle metabolically activated by rewarding stimulation or by reward-blocking doses of pimozide.

Using [14C]-2-deoxyglucose autoradiography, we determined which forebrain and diencephalic areas showed metabolic alterations in response to unilateral electrical stimulation of the posterior medial forebrain bundle at parameters chosen to produce a just-submaximal rewarding effect. At these parameters, only a few areas were activated. There was no detectable activation anterior or dorsal to the genu of the corpus callosum. Just anterior to the anterior commissure, there was strong activation of the vertical limb of the diagonal band of Broca, with a focus in the nucleus of the diagonal band. Just posterior to the anterior commissure, there was strong activation of compartment "c" of the medial forebrain bundle (MFB), with weaker activation of the bed nucleus of the stria terminalis and the medial preoptic area. At midhypothalamic levels, the dorsolateral, dorsomedial, and ventral MFB all showed activation. There was bilateral suppression of activity in the lateral habenula. Activation appeared to end in the anterior ventral tegmental area of Tsai. Reward-blocking doses of the neuroleptic pimozide activated the caudate and the lateral habenula but did not alter any of the unilateral effects of stimulation. Using longer pulse durations and/or shifting the site of stimulation to the substantia nigra activated many of the systems not activated in the first experiment, including all of the major dopaminergic projection systems, proving the capacity of the technique to reveal activation of these systems. The results permit one to define a discrete projection system that merits electrophysiological investigation as a likely substrate for the rewarding effect of MFB stimulation. They also suggest that dopaminergic projection systems may not form part of the reward pathway itself.

Animals↗
PubMed1988

The contribution of the rewarded and the non-rewarded stimulus in visual discrimination learning in mice.

The relative contribution of the rewarded and non-rewarded stimulus in the learning of a visual discrimination task in various species is unclear. A number of different parameters have been suggested as influencing the importance of the one over the other, among them the type of reinforcement. Our results show that with both positive reinforcement (using water as reward after a correct choice, and no reinforcement after an incorrect choice) and negative reinforcement (electroshock punishment after an incorrect choice) mice use the position of the incorrect stimulus as a cue for the discrimination. Mice trained by positive reinforcement without the added negative reinforcement of blocking the door on which the incorrect stimulus is projected, do not learn a brightness discrimination task. This suggested that the added negative reinforcement of the closed door had a strong influence on the learning behaviour in our experiments.

Animals↗
PubMedDate not supplied

Carbon monoxide exposure reduces the rewarding quality of brain-stimulation reward in rats.

The effect of carbon monoxide (CO) exposure on hypothalamic brain-stimulation reward (BSR) was examined. Rats were trained in a procedure that daily determined their stimulus duration threshold (SDT), that is, the shortest electrical stimulus to the posterior lateral hypothalamus that would support discrete-trial leverpress responding for BSR. After a stable SDT baseline was established using a single response lever, rats were exposed to 0, 5, 10, 20, and 40 ml/kg pure CO by IP injection. The SDT was significantly elevated by the 40 ml/kg exposure (corresponding to approximately 65% carboxyhemoglobin in the blood) compared to control exposures of an equal volume. No change was observed in response rate at any dose in this 1-lever task. No tolerance was observed when 40 ml/kg CO exposure was repeated on alternating days for 14 exposures, but a small reduction in response rate was observed in this procedure. When rats of a second group were required to alternate responses on two levers some distance apart, SDT was elevated by the highest exposure (40 ml/kg) as before. Additionally, response rate was also significantly suppressed by the highest exposure in this 2-lever task. The results support the view that CO has a direct effect on brain reward systems assessed by the SDT task. Response rate changes due to CO exposure may be due to both direct effects on brain reward systems and other effects such as hypoxia-induced fatigue.

Animals↗
PubMed2006

Lidocaine inactivation of the ventral pallidum affects responding for brain stimulation reward more than it affects the stimulation's reward value.

The ventral pallidum (VP) supports self-stimulation and has anatomical connections that suggest it could be linked to medial forebrain bundle (MFB) self-stimulation. Dorsal VP appears to be more related to dorsal striatopallidum and thus to cognitive control of movement, while ventral VP appears to be more related to linking motivation to action. In this study we challenged MFB self-stimulation by temporarily inactivating dorsal and ventral VP. We assessed changes in performance capacity and stimulation reward value using the rate-frequency curve shift paradigm. VP inactivation, especially in the ventral aspect of the VP ipsilateral to the stimulation site, was more likely to substantially impair maximum response rate than to affect the frequency required to maintain half-maximal responding. These effects were transient, typically disappearing within 20 min following inactivation. Contralateral inactivation was relatively ineffective and bilateral inactivation was surprisingly less effective than ipsilateral inactivation alone, although bilaterally symmetric injection sites were largely confined to the dorsal VP. The fact that inactivation-induced changes in maximum response rate were more prominent than changes in the frequency required to maintain half-maximal responding suggests a role for the ventral VP in linking reward to responding rather than detecting or computing reward value.

Anesthetics, Local↗
PubMed1999

Choosing between small, likely rewards and large, unlikely rewards activates inferior and orbital prefrontal cortex.

Patients sustaining lesions of the orbital prefrontal cortex (PFC) exhibit marked impairments in the performance of laboratory-based gambling, or risk-taking, tasks, suggesting that this part of the human PFC contributes to decision-making cognition. However, to date, little is known about the particular regions of the orbital cortex that participate in this function. In the present study, eight healthy volunteers were scanned, using H(2)(15)0 PET technology, while performing a novel computerized risk-taking task. The task involved predicting which of two mutually exclusive outcomes would occur, but critically, the larger reward (and penalty) was associated with choice of the least likely outcome, whereas the smallest reward (and penalty) was associated with choice of the most likely outcome. Resolving these "conflicting" decisions was associated with three distinct foci of regional cerebral blood flow increase within the right inferior and orbital PFC: laterally, in the anterior part of the middle frontal gyrus [Brodmann area 10 (BA 10)], medially, in the orbital gyrus (BA 11), and posteriorly, in the anterior portion of the inferior frontal gyrus (BA 47). By contrast, increases in the degree of conflict inherent in these decisions was associated with only limited changes in activity within orbital PFC and the anterior cingulate cortex. These results suggest that decision making recruits neural activity from multiple regions of the inferior PFC that receive information from a diverse set of cortical and limbic inputs, and that the contribution of the orbitofrontal regions may involve processing changes in reward-related information.

Adult↗
PubMed1990

Effect of lesions of areas of brain--stimulation reward of one region of brain on operant behaviour for receiving electrical stimulation into sites of another region and on operant behaviour for food reward.

It was aimed to study the effects of lesions of a self-stimulation (SS) area of one region of brain on the SS of another region, and on feeding behaviour in adult Wistar rats (males). The two regions proposed for study were the lateral hypothalamus (LH) and the substantia nigra-ventral tegmental area (SN-VTA). The objective was to elucidate whether each region had its own neural organization for SS behaviour or not, and whether the neural substrates of SS behaviour and feeding behaviour were one, or separate. Four bipolar electrodes were implanted bilaterally in LH and SN-VTA in each rat, and their SS pedal press rates for rewarding electrical stimulations were characterised. The rats were also trained in operant conditioning paradigm for receiving reward of food grains in FR-30 schedule. Their free-field food intake in home cages was measured. Later, electrolytic lesions of the four electrode sites were made one after another at 2-day intervals through the same biopolar electrodes. After each lesioning, the SS of the same and of the other electrode sites, and the operant performance of FR-30 food reward schedule, and daily free-field food intake (in home cage) were determined. Lesions of the LH SS site always disrupted SS-of contralateral LH but not of SN-VTA SS. Lesions of SN-VTA had not modified contralateral SN-VTA SS. A study of effects of ipsilateral lesions of LH SS site on SN-VTA SS, or of lesions of SN-VTA SS site on LH SS, revealed a range of changes, as were also effects on the FR-30 operant performance and daily food intake. Medium size lesions of SS area made in one region affected the SS of that area but not usually the SS of the other region. Large lesions of one region affected the SS of the other regions also. With large lesions, feeding behaviour also was affected, firstly of the operant type and secondly the free-field type.

Animals↗
PubMed2006

Reward value coding distinct from risk attitude-related uncertainty coding in human reward systems.

When deciding between different options, individuals are guided by the expected (mean) value of the different outcomes and by the associated degrees of uncertainty. We used functional magnetic resonance imaging to identify brain activations coding the key decision parameters of expected value (magnitude and probability) separately from uncertainty (statistical variance) of monetary rewards. Participants discriminated behaviorally between stimuli associated with different expected values and uncertainty. Stimuli associated with higher expected values elicited monotonically increasing activations in distinct regions of the striatum, irrespective of different combinations of magnitude and probability. Stimuli associated with higher uncertainty (variance) elicited increasing activations in the lateral orbitofrontal cortex. Uncertainty-related activations covaried with individual risk aversion in lateral orbitofrontal regions and risk-seeking in more medial areas. Furthermore, activations in expected value-coding regions in prefrontal cortex covaried differentially with uncertainty depending on risk attitudes of individual participants, suggesting that separate prefrontal regions are involved in risk aversion and seeking. These data demonstrate the distinct coding in key reward structures of the two basic and crucial decision parameters, expected value, and uncertainty.

Adult↗
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↗
PubMed2001

A concept of welfare based on reward evaluating mechanisms in the brain: anticipatory behaviour as an indicator for the state of reward systems.

In this review we attempt to link the efficiency by which animals behave (economy of animal behaviour) to a neuronal substrate and subjective states to arrive at a definition of animal welfare which broadens the scope of its study. Welfare is defined as the balance between positive (reward, satisfaction) and negative (stress) experiences or affective states. The state of this balance may range from positive (good welfare) to negative (poor welfare). These affective states are momentary or transient states which occur against the background of and are integrated with the state of this balancing system. As will be argued the efficiency in behaviour requires that, for instance, satisfaction is like a moving target: reward provides the necessary feedback to guide behaviour; it is a not steady-state which can be maintained for long. This balancing system is reflected in the brain by the concerted action of opioid and mesolimbic dopaminergic systems. The state of this system reflects the coping capacity of the animal and is determined by previous events. In other words, this integrative approach of behavioural biology and neurobiology aims at understanding how the coping capacity of animals may be affected and measured. We argue that this balancing system underlies the economy of behaviour. Furthermore we argue that among other techniques anticipation in Pavlovian conditioning is an easy and useful tool to assess the state of this balancing system: for estimating the state of an animal in terms of welfare we focus on the conditions when an animal is facing a challenge.

Journal Article↗
PubMed2001

Mouse strain differences in opiate reward learning are explained by differences in anxiety, not reward or learning.

Gene-targeting techniques to produce null mutations provide a powerful method for evaluating the contribution of particular candidate genes involved in motivation. The embryonic stem cell lines in which homologous recombination is undertaken are derived from 129 mice, but because of the impoverished performance of 129 mice on a number of behavioral tasks, mice chimeric for the mutation are often bred with a C57BL/6 mouse strain. Thus, an examination of both parental strains is important in the study of the knock-out mice. Although the C57BL/6 behavioral phenotype is well documented, details of the 129 phenotype have not been the focus of study until recently. We investigated opiate motivation in both 129/SvJ and C57BL/6J mouse strains to determine whether, and under what circumstances, the 129/SvJ mouse exhibited motivated behavior toward opiates. 129/SvJ mice required both drug and contextual cues to demonstrate morphine conditioned place preferences on test day, whereas C57BL/6J mice required only contextual cues to express opiate place conditioning. Pentobarbital and diazepam but not saline, cocaine, or naloxone could substitute for morphine on test day in 129/SvJ mice, demonstrating that morphine indeed has rewarding motivational valence in the 129/SvJ mouse strain. This critical, interoceptive cue in 129/SvJ mice on test day may be the anxiolytic properties of the effective drugs. Therefore, some deficits observed in 129 mice and mice harboring this genetic background may be attributed to high levels of anxiety during the retrieval period rather than to sensory, learning, or motivational deficits.

Animals↗
PubMedDate not supplied

Rewarding clinical competence in the ICU: using outcomes to reward performance.

The rising acuity of hospitalized patients requires that critical care nurses maintain a high level of clinical expertise. Expert skill levels (critical thinking, technical skills, and interpersonal skills) of clinicians improve patient outcomes that translates into savings for the institution through shorter length of stay and decreased frequency of re-admissions. The authors outline the steps to follow in developing a theory-based career advancement plan that encourages and rewards clinical competence.

Career Mobility↗