The role of brain stimulation priming effects in self-deprivation

Choice of brain stimulation reward (BSR) over biologically necessary substances in some self-stimulating animals is referred to as self-deprivation. In several recent papers, it has been argued that this phenomenon is produced by the rewarding aspects of the brain stimulation. This conclusion is partially based on data showing that self-deprivation and brain stimulation reward increase and decrease in a similar manner in response to changes in the brain stimulation parameters. However, the priming aspects of the brain stimulation also fluctuate with changes in stimulation parameters. Therefore, changes in the priming rather than the rewarding aspects of the brain stimulation could be responsible for self-deprivation. To determine whether the priming effects of brain stimulation play an important role in self-deprivation, rats with bipolar stimulating electrodes were given the choice between BSR and food. Time-outs were enforced within each BSR/food competition session. Since priming effects decay over time, increasing time-out length should have decreased self-deprivation due to decay of priming. It was found that time-out length did not affect the degree of self-deprivation. It was concluded that self-deprivation is not mediated by the priming aspects of brain stimulation.     

Measuring threshold shifts for brain stimulation reward using the method of limits.

Thresholds determined from the frequency of pulses and the current for rewarding brain stimulation were obtained from rats with lateral hypothalamic electrodes. The threshold, defined as the frequency or current corresponding to one-half the maximum response rate, was interpolated from reward summation functions. Daily trials of both ascending and descending sequences of frequency and current yielded no significant difference between order of presentation. While there was more variability in the maximum response rates across the sessions, neither frequency- nor current-based threshold evaluations yielded significant rate effects. Our findings suggest that the threshold procedure is generally not influenced by the sequence of delivery of stimulus values and, thus, may be regarded as a reliable measure of the reinforcing properties of brain-stimulation reward.     

Preference paradigm: provides better self-stimulation reward discrimination than a rate-dependent paradigm

To obtain a better understanding of how well the Y-maze preference test paradigm indexes electrical brain stimulation reward, the present experiment compared the abilities of this rate-independent paradigm and a rate-dependent paradigm to assess the rewarding effectiveness of brain stimulation. The rate-dependent paradigm used was an operant chamber. The results showed that over a wide range of stimulation parameters the rate-independent paradigm provided a better assessment of the rewarding effectiveness of the brain stimulation than did the rate-dependent paradigm.     

Runway performance of rats for brain-stimulation or food reward: effects of hunger and priming.

In a runway paradigm, pretrial electric stimulation of the brain (ESB), food deprivation, and to a lesser extent water deprivation increased the running speed of rats to an ESB reward. The trial-by-trail course of the change in running speed after the manipulation of food deprivation resembled the steplike performance effect seen when pretrial priming ESB is changed rather than the incremental learning effect seen when the response contingent ESB is changed. In a second experiment, pretrial ESB enhance rats' performance for an ESB reward, but act in opposing directions rats' performance for a food reward. Implications for Deutsch's model of self-stimulation are discussed.     

Reinforcement contrast effects on the rewarding and aversive components of intracranial stimulation

Rats performing a free-operant locomotor response in a shuttlebox to initiate and then escape medial diencephalic stimulation were tested daily on a randomized sequence of three stimulation intensities. In spite of a 1-hr interval between stimulation intensity changes, substantial and graded reinforcement contrast effects were obtained. “Elation” effects were obtained both on the rewarding (latency to initiate) and the aversive (latency to escape) components of stimulation whereas “depression” effects were found only on the measure of reward.     

奖赏性线索启动和调控视觉搜索额顶网络的神经机制

近期关于奖赏性信息与视觉搜索任务的交互作用研究体现在两个层面, 其一是施加外部奖赏能够影响被试的视觉搜索反应时和正确率, 其二是搜索目标本身具有奖赏特性也能够影响行为反应。但是, 奖赏性信息对负责视觉搜索的额顶注意网络的动态启动和调控作用仍不清楚。本研究结合Posner空间预提示范式和视觉搜索范式, 采用快速事件相关功能磁共振成像技术, 分别操纵线索提示阶段的线索奖赏属性(奖赏性vs.非奖赏性)和线索空间注意属性(有效提示目标位置vs.无效提示目标位置), 并操纵目标搜索阶段的目标属性(奖赏性vs.非奖赏性), 探讨以下两个核心问题：(1)在线索提示阶段, 奖赏性线索产生的自上而下注意准备信号的神经基础, 以及该神经基础与传统的空间注意准备信号的异同; (2)在目标搜索阶段, 奖赏性线索对负责视觉搜索的额顶注意网络产生的启动和调控作用, 重点考察对正确的奖赏性信息的定向过程和对错误的奖赏性信息的重新定向过程。     

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.     

Delayed backward conditioning of place preference induced by wheel running in rats

Backward conditioning of place preference has been obtained in hungry rats when wheel running (the rewarding US) is followed immediately by exposure to a distinctive chamber (the CS). We tested whether such backward conditioning would occur with a 10-min delay. In each of four paired exposures, a period of wheel running (2 or 22 h, in separate experiments) was followed by 10 min in the home cage and then 30 min in the CS chamber. Control rats were put in the CS chamber without wheel running. In other similar experiments, a 0-, 10-, or 30-min delay separated wheel running from exposure to the CS chamber. Reliable conditioned place preference (CPP) occurred when the delay was 0 or 10 but not 30 min. The strength of CPP decreased as the delay increased. These findings imply that the reward process initiated by wheel running remains active for some time after running stops. They support the view that the suppression of feeding produced by wheel running in hungry rats (activity anorexia) is mediated by this reward process.     

Wild capuchin monkeys anticipate the amount of ripe fruit in natural trees

Tropical forests have a high diversity of tree species which have very low densities and vary across time in their seasons of peak fruiting and maturation rates. As evidence of the ability of primates to track or anticipate changes in fruit production at individual trees, researchers have used the increased speed of primate groups toward more rewarding food patches. We analyzed the speed of approach to natural trees of wild capuchin monkeys under the effect of scramble competition, after excluding any plausible visual, olfactory and auditory cues. We conducted all-day group follows of three habituated capuchin groups at Iguazú National Park, Argentina, collecting data on ranging behavior and patterns of visits to fruit trees in relation with their location and fruit availability. Travel speed varied according to the expected reward at a feeding tree, increasing as rewards increased from low values, but decreasing again at very high values. Also, travel speed varied with time of day, decreasing from the time of first activity as the monkeys became less hungry, and increasing again toward late afternoon. Measures of unripe fruit cover did not explain variation in travel speed at any distance from a focal tree. Our data imply that, after excluding sensory cues, capuchins appear to anticipate time-varying ripe fruit quantity of natural resources, suggesting that they use memory of tree location and anticipation of fruit maturation. We also confirm that speed is a good measure about expectations of resources, as has been shown in previous studies.     

Putting behavior on hold decreases reward value of need-instrumental objects outside of awareness

We examined whether cues that put impulsive behavior towards rewarding objects on hold reduces the value of the rewarding objects outside of conscious awareness. We manipulated the reward value of water by making participants thirsty, or not. Next, a bottle of water was subliminally presented in a go/no-go task, and paired with either go cues or no-go cues (putting behavior on hold). Subsequently, as a measure of reward value of water, participants estimated the size of water objects. Results showed that repeatedly withholding behavior towards water reduced the perceived size of water objects, but only when participants were made thirsty. These results suggest that withholding impulsive behavior towards objects that serve basic needs nonconsciously reduces reward value of these objects. Implications for nonconscious behavior regulation are briefly discussed.     

The impact of monetary stimuli on object-based attention

Previous research has implied that monetary reward to target location (a reward for spatial properties) can affect object-based attention, but no study has directly investigated the influence of monetary objects (a reward for object properties) on object-based attention. Thus, it is unclear whether and how monetary objects can affect object-based attention. To experimentally investigate this problem, this study adapted the well-established two-rectangle paradigm. In Experiment 1, either two 100-yuan notes or two 1-yuan notes were presented to participants. We found an object-based effect with faster responses to targets at an uncued position on the cued object compared to those at an equidistant position on the uncued object; the effect was similar in 100-yuan and 1-yuan note trials. In Experiment 2, two notes (one 100-yuan and one 1-yuan) were simultaneously presented to participants, and cue location (100-yuan, 1-yuan) was manipulated. We found a greater object-based effect when the cue appeared on the 100-yuan note than on the 1-yuan note. These results suggest that the rewarding property of objects can affect object-based attention by means of altering object salience.     

Neural substrate for brain stimulation reward in the rat: cathodal and anodal strength-duration properties.

The trade-off between current strength and duration of a stimulating pulse was studied for the rewarding and priming effects of brain stimulation reward (BSR). With cathodal pulses, strenght-duration functions for BSR had chronaxies of .8-3 msec. No differences were observed between the results for rewarding and priming effects. With anodal pulses. strength-duration curves were parallel to the cathodal curves at pulse durations of .1-5 msec, but at pulse durations greater than 5 msec the anodal curves showed a greater drop in required current intensity than did the cathodal curves. The parallel portion of the anodal curves was interpreted as due to anode-make excitation, and the drop at longer pulse durations was interpreted as due to anode-break excitation. Cathodal strength-duration functions for the motor effect elicited through the BSR electrodes had chronaxies of .15-.48 msec. Measurements of the latency of the muscle twitch confirmed that anode-make and anode-break excitation occurred, the latter becoming evident at pulse durations as brief as .3-.4 msec. The results provide quantitative characterization of cathodal and anodal strength-duration properties of the neural substrate for BSR and are discussed in terms of their value in guiding electrophysiological investigation of that substrate.     

焦虑情绪对奖赏学习的影响

焦虑是在我们日常生活中占据重要地位的一种情绪, 对人类的决策行为能够产生显著影响。探讨决策研究的重要领域--奖赏学习, 可以帮助我们更深入地认识焦虑情绪在决策过程中扮演的角色。过往研究者较少关注焦虑对奖赏学习的潜在影响, 而且已有研究在实验技术和任务范式方面存在一定的局限性。考虑到奖赏学习概念的复杂性, 为了全面地考察个体焦虑水平与奖赏学习的关系, 本文作者建议设置不同类型的奖赏学习情境, 例如概率学习、联结学习、逆向学习和社会学习等。在上述各类不同任务中, 个体焦虑水平对奖赏学习能力的影响模式可能并不一致, 有待研究者们进行深入探讨。     

The Environmental Reward Observation Scale (EROS): development, validity, and reliability

Researchers acknowledge a strong association between the frequency and duration of environmental reward and affective mood states, particularly in relation to the etiology, assessment, and treatment of depression. Given behavioral theories that outline environmental reward as a strong mediator of affect and the unavailability of an efficient, reliable, and valid self-report measure of environmental reward, we developed the Environmental Reward Observation Scale (EROS) and examined its psychometric properties. In Experiment 1, exploratory factor analysis supported a unidimensional 10-item measure with strong internal consistency and test-retest reliability. When administered to a replication sample, confirmatory factor analysis suggested an excellent fit to the 1-factor model and convergent/discriminant validity data supported the construct validity of the EROS. In Experiment 2, further support for the convergent validity of the EROS was obtained via moderate correlations with the Pleasant Events Schedule (PES; MacPhillamy & Lewinsohn, 1976). In Experiment 3, hierarchical regression supported the ecological validity of the EROS toward predicting daily diary reports of time spent in highly rewarding behaviors and activities. Above and beyond variance accounted for by depressive symptoms (BDI), the EROS was associated with significant incremental variance in accounting for time spent in both low and high reward behaviors. The EROS may represent a brief, reliable and valid measure of environmental reward that may improve the psychological assessment of negative mood states such as clinical depression.     

The relationship between reward and probability: Evidence that exploration may be intrinsically rewarding

ABSTRACT

The probability of an event occurring and the reward associated with the event can both modulate behaviour. Response times are decreased to stimuli that are either more rewarding or more likely. These two factors can be combined to give an Expected Value (EV) associated with the event (i.e., probability of the event x reward magnitude). In four experiments we investigate the effect of reward and probability on both saccadic and manual responses. When tested separately we find evidence for both a reward and probability effect across response types. When manipulations of reward magnitude and probability of the event were combined, the probability modulations dominated and these data were not well accounted for by the EV. However, a post-hoc model that included an additional intrinsic reward associated with responding provided an excellent account for the data. We argue that reward consists of both an explicit and intrinsic component. In our task, the saccadic and manual responses are linked to the information provided by the targets and the goals of the task, and successful completion of these is in itself rewarding. As a result, targets associated with a higher probability of being presented have a higher intrinsic reward.     

Grouping, chunking, memory, and learning

An example of grouping is dividing a long series of digits into two or more smaller units by, for example, pausing for a short time between items within groups but for a longer time between groups. Grouping, virtually neglected in animal learning, was examined in each of five rat investigations reported here in which a series of two or more runway trials was either grouped together with or apart from a terminal large reward trial. It was found that running speed on early small reward trials in the series was greater when prior trials were grouped together with rather than apart from the terminal large reward trial and this when the intertrial interval was short, 20 sec, or long, 20 to 40 min. Three possible explanations of the present findings were examined: a reward schedule view, a rule-learning view, and an anticipation view based on memory. The most feasible of these explanations, it was suggested, was the anticipation view. According to this view, when prior trials are grouped together with a terminal large reward, there is a tendency for the rat to anticipate the terminal large reward well before its scheduled occurrence, elevating running speed on earlier small reward trials. Such anticipation occurs, it was suggested, because when trials are grouped together the memory of each reward event in the series is retrieved on each subsequent trial, including the remote terminal large reward trial, where it becomes a signal for large reward. Thus the present results implicate not merely adjacent associations—associations between adjacent events—but also the highly controversial remote associations—associations between two events separated not only in time but by one or more intervening events as well.     

Polysynaptic potentiation at different levels of rat olfactory pathways following learning

This study was aimed at investigating the consequences of learning on late polysynaptic components of evoked field potential signals recorded in parallel at different levels of the olfactory pathways. For this, evoked field potentials induced by electrical stimulation of the olfactory bulb were recorded simultaneously in the anterior piriform cortex, the posterior piriform cortex, the lateral entorhinal cortex, and the dentate gyrus. The different parameters of late components were measured in each site before and after completion of associative learning in anesthetized rats. In the learning task, rats were trained to associate electrical stimulation of one olfactory bulb electrode with the delivery of sucrose (positive reward) and stimulation of a second olfactory bulb electrode with the delivery of quinine (negative reward). In this way, stimulation of the same olfactory bulb electrodes used for inducing field potentials served as a discriminative cue in the learning paradigm. The data confirmed previous observation that learning was associated with a lowering in late-component-1 intensity of induction in the posterior piriform cortex. The use of simultaneous recording allowed us to further specify the consequences of learning on late-component distribution in the studied network. Indeed the data showed that whereas before learning, late component 1 was rather uniformly distributed among the recorded sites; following learning, its expression was facilitated preferentially in the posterior piriform cortex and lateral entorhinal cortex. Furthermore, learning was accompanied by the emergence of a new late component (late component 2), which occurred simultaneously in the four recording sites. The possible involvement of potentiation of polysynaptic components in recognition and/or consolidation processes will be discussed.     

Extinction of a running response as a function of reinforcement magnitude

Four groups of rats were trained on different sucrose solutions in a straight runway. Terminal running speed was a monotonic function of reinforcement magnitude. After training each group was subdivided, one subgroup being extinguished under spaced, the other under massed conditions. In spaced extinction the animals trained on non extreme reward magnitudes showed most resistance to extinction. It was concluded that resistance to extinction is an inverted U-shaped function of reinforcement magnitude found in training. The massed extinction trials were conducted with a very short inter-trial interval. The animals showed an immediate drop in running speed followed by a gradual recovery and a subsequent decline. The number of trials taken to reach the peak recovery speed was a function of reinforcement magnitude found in training. Results on both massed and spaced extinction trials were interpreted in terms of the facilitatory and inhibitory effects of momentary and conditioned frustration.     

The effect of central and peripheral field stimulation on the rise time and gain of human optokinetic nystagmus

We wished to examine the spatial (gain) and temporal (rise time) properties of human optokinetic nystagmus (OKN) as a function of stimulus velocity and field location. Stimuli were either M-scaled random dots or vertical stripes that moved at velocities between 20-80 deg s(-1). Three field conditions were examined: full field; a 20 deg central field; and a 12.5 deg central-field mask. OKN gain was found to be significantly affected by stimulus velocity and stimulus location, with the higher stimulus velocities and the 12.5 deg central-field mask giving lower gains. Steady-state gains for all three field conditions were not found to be affected by prior adaptation to stationary or moving stimuli. The 63% rise time was found to be significantly affected by the stimulus velocity, whereas this was not the case for the 90% rise time. Neither rise time was found to be significantly affected by the field location. These results indicate that, although the effectiveness (gain) of peripheral retina is lower than that of the central retina during optokinetic stimulation, the peripheral retina has access to common mechanisms responsible for the fast component of OKN.     

The interaction of hunger and thirst in the rat

Two groups of rats were given a series of trials in an enclosed runway with a food reward at the end, one group being run hungry, the other hungry plus thirsty. Then each group was split into three sub-groups: one run hungry, the second thirsty and the other hungry plus thirsty, in each case without food reward.

It was found that, whereas on the rewarded runs the extra, “irrelevant,” thirst increased running speed, on unrewarded runs it had the opposite effect and slowed up performance. Thus on unrewarded runs the two sub-groups running thirsty, and hungry plus thirsty, ran as slowly as those running hungry. Differences were found not to depend on whether the animals had been hungry or hungry plus thirsty on previous rewarded runs.

The interaction of primary needs therefore depends on the external situation. This can be accounted for in terms of the Pavlovian theories of mutual induction and conditioning, but not in terms of Hull's theory of “irrelevant drives.”