奖赏敏感性在冲动性饮食行为中的作用

肥胖会导致癌症、心脏病、糖尿病等诸多健康问题,而冲动性饮食是肥胖的一个重要影响因素。厘清奖赏敏感性在冲动性饮食中的作用,有助于深入理解冲动性饮食行为。本文介绍了奖赏敏感性的概念、涉及的主要研究领域、生物学基础及测量;整理归纳出奖赏敏感性影响冲动性饮食的三种可能路径:通过注意力偏向影响对享乐性食品的感知、影响消费欲望及随后的自我控制;文章最后指出了基于奖赏敏感性对冲动性饮食进行拓展研究的可能方向。     

Discrimination between reinforced action patterns in the rat

Laboratory rats were rewarded for face-washing, rearing, or scratching by being given the opportunity to press retractable levers for food reward. Yoked control animals received the same number of lever presentations and food rewards, but did not have to face-wash, rear, or scratch to obtain the levers. The experimental animals showed increases in number of bouts of reinforced target behavior above control levels, and the total amount of time spent face-washing increased when a 1.5-sec criterion for reinforced bout length was introduced. The activities in this experiment were made to serve a discriminative as well as an instrumental function, since the cue to tell the rat which lever to press for reward when the levers were presented was the activity that the rat had engaged in to obtain lever presentation. In two separate experiments high levels of discrimination between behaviors were obtained. Discrimination was worse following scratching than after other actions, and scratching also showed relatively poor instrumental conditioning. The relationship between Pavlovian and instrumental conditioning processes in this situation is discussed.     

Using pavlovian higher-order conditioning paradigms to investigate the neural substrates of emotional learning and memory

In first-order Pavlovian conditioning, learning is acquired by pairing a conditioned stimulus (CS) with an intrinsically motivating unconditioned stimulus (US; e.g., food or shock). In higher-order Pavlovian conditioning (sensory preconditioning and second-order conditioning), the CS is paired with a stimulus that has motivational value that is acquired rather than intrinsic. This review describes some of the ways higher-order conditioning paradigms can be used to elucidate substrates of learning and memory, primarily focusing on fear conditioning. First-order conditioning, second-order conditioning, and sensory preconditioning allow for the controlled demonstration of three distinct forms of memory, the neural substrates of which can thus be analyzed. Higher-order conditioning phenomena allow one to distinguish more precisely between processes involved in transmission of sensory or motor information and processes involved in the plasticity underlying learning. Finally, higher-order conditioning paradigms may also allow one to distinguish between processes involved in behavioral expression of memory retrieval versus processes involved in memory retrieval itself.     

Emotional eating and Pavlovian learning: evidence for conditioned appetitive responding to negative emotional states

Appetitive learning has been demonstrated several times using neutral cues or contexts as a predictor of food intake and it has been shown that humans easily learn cued desires for foods. It has, however, never been studied whether internal cues are also capable of appetitive conditioning. In this study, we tested whether humans can learn cued eating desires to negative moods as conditioned stimuli (CS), thereby offering a potential explanation of emotional eating (EE). Female participants were randomly presented with 10 different stimuli eliciting either negative or neutral emotional states, with one of these states paired with eating chocolate. Expectancy to eat, desire to eat, salivation, and unpleasantness of experiencing negative emotions were assessed. After conditioning, participants were brought into a negative emotional state and were asked to choose between money and chocolate. Data showed differential conditioned responding on the expectancy and desire measures, but not on salivation. Specific conditioned effects were obtained for participants with a higher BMI (body mass index) on the choice task, and for participants high on EE on the unpleasantness ratings. These findings provide the first experimental evidence for the idea that negative emotions can act as conditioned stimuli, and might suggest that classical conditioning is involved in EE.     

What is in a word? No versus Yes differentially engage the lateral orbitofrontal cortex

The words "No" and "Yes" are involved in conditioning to prohibit or encourage behavior, respectively. The authors, therefore, hypothesized that these words would be attributed to endogenous valence, activating neuronal circuits involved with valence and emotional control. Functional MRI (fMRI) at 4 Tesla was used to record regional brain activity while participants were exposed to emphatic vocalizations of the words. Results showed that No and Yes were associated with opposite brain-behavior responses; while No was negatively valenced, produced slower response times, and evoked a negative signal in the right lateral orbitofrontal cortex (OFC), Yes was positively valenced, produced faster response times, and evoked a positive signal in a contiguous region of the OFC. Attribution of negative valence to No and trait anger control were associated with increased responsivity of the OFC to No. Inasmuch as sensitivity to the prohibitive command No develops during childhood through interaction with primary caregivers as the first social objects, our findings may implicate the lateral OFC in the neurobiology of emotion regulation and subsequent social development.     

Imitation of mother’s inappropriate food preference in weanling kittens

Experiments were performed on four mother cats and their 22 kittens from 7 litters. Each mother was trained to eat banana or mashed potato in the presence of meat pellets in order to get a hypothalamic stimulation reward. Eighteen of twenty-two weanling kittens which accompanied the mother during the session imitated the mother in eating banana or potato and ignored meat pellets. The imitation of the mother started not earlier than at 35 days of age and in most kittens (10 of 18) began between 49 and 56 days of age. The kittens which ate banana or potato with the mother also ate that food when tested alone after weaning at 9 to 27 weeks of age, either during 10 min sessions in the experimental compartment or during 24 hr tests in the home compartment. When banana was offered to 9 control 13–23 week old kittens (of three other mothers) who never before had eaten that food or had seen their mother eat it, 8 of them did not consume banana during three 24 hr tests. Some consumption, however, occurred in the ninth kitten during the third of these tests. It has been concluded that weanling kittens in the period of transition from maternal to independent feeding tend to imitate the mother in food preferences, even if the food chosen by the mother is unusual for their species. The food preferences acquired through the imitation of the mother may influence the food preferences at the later stages of life.     

Stimulus-driven and goal-driven effects on Pavlovian associative reward learning

It has been shown that pure Pavlovian associative reward learning can elicit value-driven attentional capture. However, in previous studies, task-irrelevant and response-independent reward-signalling stimuli hardly competed for visual selective attention. Here we put Pavlovian reward learning to the test by manipulating the extent to which bottom-up (Experiment 1) and top-down (Experiment 2) processes were involved in this type of learning. In Experiment 1, the stimulus, the colour of which signalled the magnitude of the reward given, was presented simultaneously with another randomly coloured stimulus, so that it did not capture attention in a stimulus-driven manner. In Experiment 2, observers performed an attentionally demanding RSVP-task at the centre of the screen to largely tax goal-driven attentional resources, while a task-irrelevant and response-independent stimulus in the periphery signalled the magnitude of the reward given. Both experiments showed value-driven attentional capture in a non-reward test phase, indicating that the reward-signalling stimuli were imbued with value during the Pavlovian reward conditioning phases. This suggests that pure Pavlovian reward conditioning can occur even when (1) competition prevents attention being automatically allocated to the reward-signalling stimulus in a stimulus-driven manner, and (2) attention is occupied by a demanding task, leaving little goal-driven attentional resources available to strategically select the reward-signalling stimulus. The observed value-driven attentional capture effects appeared to be similar for observers who could and could not explicitly report the stimulus–reward contingencies. Altogether, this study provides insight in the conditions under which mere stimulus–reward contingencies in the environment can be learned to affect future behaviour.     

Post-training amphetamine administration enhances memory consolidation in appetitive Pavlovian conditioning: Implications for drug addiction

It has been suggested that some of the addictive potential of psychostimulant drugs of abuse such as amphetamine may result from their ability to enhance memory for drug-related experiences through actions on memory consolidation. This experiment examined whether amphetamine can specifically enhance consolidation of memory for a Pavlovian association between a neutral conditioned stimulus (CS-a light) and a rewarding unconditioned stimulus (US-food), as Pavlovian conditioning of this sort plays a major role in drug addiction. Male Long-Evans rats were given six training sessions consisting of 8 CS presentations followed by delivery of the food into a recessed food cup. After the 1st, 3rd, and 5th session, rats received subcutaneous injections of amphetamine (1.0 or 2.0 mg/kg) or saline vehicle immediately following training. Conditioned responding was assessed using the percentage of time rats spent in the food cup during the CS relative to a pre-CS baseline period. Both amphetamine-treated groups showed significantly more selective conditioned responding than saline controls. In a control experiment, there were no differences among groups given saline, 1.0 or 2.0 mg/kg amphetamine 2 h post-training, suggesting that immediate post-training amphetamine enhanced performance specifically through actions on memory consolidation rather than through non-mnemonic processes. This procedure modeled Pavlovian learning involved in drug addiction, in which the emotional valence of a drug reward is transferred to neutral drug-predictive stimuli such as drug paraphernalia. These data suggest that amphetamine may contribute to its addictive potential through actions specifically on memory consolidation.     

Autonomic conditioning to monetary and social stimuli and aggression in children

Poor conditioning to punishment, such as loud tones or electric shock, has been proposed as an important factor involved in the etiology of aggressive and psychopathic behavior. However, it is not known whether the association holds when monetary or social stimulus is used as the unconditioned stimulus, and if aggressive individuals also have impaired conditioning to rewards. In this study, skin conductance responses in a conditioning task involving both monetary/social reward and punishment as unconditioned stimuli were assessed in 340 male and female 8‐ to 9‐year‐old children from the community. Children reported their reactive and proactive aggression using the Reactive and Proactive Aggression Questionnaire (RPQ; Raine et al., 2006). Results showed that monetary/social reward and punishment were effective in eliciting physiological classical conditioning in children, and that reduced reward conditioning was associated with high levels of proactive aggression in particular. Findings highlight the importance of distinguishing between reactive and proactive aggression when examining antisocial behavior in children, and suggest that reward‐oriented treatment programs may not be effective for children with more proactive, instrumental aggressive behavior.

     

The operation of an acquired drive in satiated rats

A series of four short experiments indicates that the behaviour of satiated rats in a runway, at the end of which they have previously been rewarded, differs significantly from the behaviour of satiated rats without previous reward in the experimental situation. The former group reach the end box more quickly after having been put in the starting box of the runway and if provided with food in the end box proceed to eat it, although they have just refused similar pieces of food in their home cages. This is shown not to be due to defective satiation or the operation of fear in the control group. When runs and feeding in the end box are separated during the training period, the previously rewarded group still shows a more vigorous response on satiated trials, indicating that it is a reward expectancy about the goal box rather than a running habit which has become “functionally autonomous”, acting as a situation-specific drive.     

Context extinction following conditioning with delayed reward enhances subsequent instrumental responding

In Experiment 1, delayed reward generated low response rates relative to immediate reward delivered with the same frequency. Lister rats exposed to delayed reward subsequently responded at a higher rate in extinction if they received nonreinforced exposure to the conditioning context after instrumental training and prior to test, compared with animals that received home cage exposure. In Experiment 2, a signaled delay of reinforcement resulted in higher rates than an unsignaled delay. Nonreinforced exposure to the conditioning context elevated response rate for subjects in the unsignaled condition relative to a home cage group, but had no effect on response rates for subjects that had received the signaled delay. In Experiment 3, following an unsignaled reinforcement delay, groups receiving either no event or signaled food in the context responded faster in extinction than groups receiving no context exposure or unsignaled food.     

Influencing food preferences of children by ‘if-then’ type instructions

Three experiments were conducted to examine the effects which ‘if-then’ instructions of the type ‘if you eat X’, then you will get Y, have on the evaluation of the foods addressed in the ‘if’ and the ‘then’ parts of the instructions, respectively. Based on research on intrinsic motivation it was hypothesized that liking for food X that one is induced to eat by means of ‘if-then’ instructions will be impaired, whereas liking for food Y offered as a reward for the consumption of X will be enhanced. Experiment 1 revealed an enhancement of liking effect for the ‘then’food lasting for at least six weeks, but no impairment of liking for the ‘if’ food. Experiment 2 explored the possibility of reducing children's dislike for foods by means of paradoxical ‘if-then’ instructions presenting the disliked food in the ‘then’ position as a reward for the consumption of another food. No significant effects were obtained in this study. Experiment 3 examined the effects of introducing yet unknown foods to children by means of ‘if-then’ instructions. Results revealed that liking for the new food is impaired when it is the ‘if’food, but is enhanced when it is offered in the ‘then’ position. Discussion is centered on the possibility that the effects of ‘if-then’ instructions are more pronounced in single trial compared to multi-trial treatment conditions.     

Linking Pavlovian Disgust Conditioning and Eating Disorder Symptoms: An Analogue Study

Although the experience of disgust is commonly endorsed among women with eating disorders, it remains unclear how to best model this emotion in relation to disordered eating. The present study sought to identify potential disgust conditioning abnormalities that may underlie the development of eating disorder symptoms. Individuals high and low in eating disorder symptoms (HED, n = 19; LED, n = 18) completed a Pavlovian conditioning procedure in which one neutral food item (conditioned stimulus; CS +) was followed by disgusting videos of individuals vomiting (unconditioned stimulus; US) and another neutral food item (CS–) was not reinforced with the disgusting video. Following this acquisition procedure, there was an extinction procedure in which both CSs were presented unreinforced. The results showed that ratings of disgust, fear, and willingness to eat the CS + and CS- did not significantly vary as a function of the conditioning phase for the LED group. However, the HED group rated the CS + as significantly more disgusting and fear inducing than the CS- after the acquisition phase and this pattern persisted after extinction. These conditioning effects were also observed to be significantly larger for disgust compared to fear. The HED group also reported being significantly less willing to eat the CS + compared to the CS- after the acquisition phase and this pattern also persisted after extinction. In the full sample, only discriminant disgust responding after acquisition was associated with the amount of calorie consumption over the 24-hour period after conditioning. These findings suggest that eating disorder symptoms may result from a heightened proneness to associate disgusting outcomes with otherwise neutral food items. This pattern of disgust learning may reinforce food avoidance in eating disorders and appears to be difficult to fully unlearn.     

Observations on the initiation of eating of new food by weanling kittens

The reaction to a new food and the initiation of its consumption were studied in daily sessions in 19 weanling kittens from four litters at 30–39 days of age. The new food consisted of canned tuna for two litters and cereal (cooked cream of wheat with 3% addition of vegetable oil and broth flavor) for the other two litters. Each litter was divided into two groups. One group was offered the new food in the presence of the mother which had been consuming it (eating cereal had to be induced in the mothers by the hypothalamic stimulation reward method). Another group of kittens received the same food in the absence of the mother. It was found that the kittens which had been offered the new food in the presence of the mother showed only a short-lasting orienting reaction and started to eat the new food on the first or second day (with a mean delay of 0.2 days). On the other hand, the kittens which had been offered the new food in the absence of the mother showed a strong orienting reaction and started to eat the new food only after several daily sessions (with a mean delay of 4.8 days). No significant difference was found between the number of days of delay in eating by kittens offered tuna and by kittens offered cereal in the absence of the mother. The initiation of consumption of the new food by these kittens was preceded by a period of playing with the plate on which the food had been placed. Additional observations showed that the fourto five-month old kittens that had eaten cereal during early training preferred that food over meat pellets; the other kittens of the same age that had eaten tuna, but no cereal, during early training refused to eat cereal when it was offered to them when they were hungry.     

Memory for time of training modulates performance on a place conditioning task in marmosets

In rodents, the expression of a reward-conditioned place preference (CPP) is regulated in a circadian pattern such that the preference is exhibited strongly at the circadian time of prior training but not at other circadian times. Because each animal is trained only at a single circadian phase, the concept of time as a context cue is derived from a rhythmic internal state rather than learned explicitly from the external cues. We now report that the same “time memory” is expressed following context conditioning in the common marmoset (Callithrix jacchus). Animals were trained at a specific time to discriminate between an unpaired context and a context paired with food reward. Marmosets were then tested for preference at circadian times that were either the same or different from the training time. Preference was expressed only when training and testing times matched. The results show that time of day learning can be generalized to this new world primate implying that a similar circadian mechanism might regulate craving for reward in diverse mammals including human beings.     

网络游戏成瘾与海洛因成瘾存在相同的神经机制吗?——基于MRI的证据

网游成瘾与海洛因成瘾具有许多相似的临床表现,但其神经机制是否相同还不得而知。综合近5年来的MRI研究发现,两类成瘾存在部分相同区域的脑结构和功能损害,且在成瘾线索诱发下二者的4个成瘾相关环路(认知控制环路、奖赏环路、动机环路和记忆-学习环路)均出现了广泛而增强的脑区激活反应。但海洛因成瘾的脑损害区域偏向更高级的认知控制环路和奖赏环路,损害范围也更广(4个环路的功能连通性均降低),而网游成瘾的脑损害主要发生在相对低级的记忆-学习环路和动机环路,损害范围也较窄(功能连通性降低只发生在认知控制和记忆-学习环路之间)。这些结果说明,两类成瘾行为的神经机制既有相同点,又有差异性。     

Role of dopamine,the frontal cortex and memory circuits in drug addiction: insight from imaging studies

Drug addiction is characterized by a set of recurring processes (intoxication, withdrawal, craving) that lead to the relapsing nature of the disorder. We have used positron emission tomography to investigate in humans the role of dopamine (DA) and the brain circuits it regulates in these processes. We have shown that increases in DA are associated with the subjective reports of drug reinforcement corroborating the relevance of drug-induced DA increases in the rewarding effects of drugs in humans. During withdrawal we have shown in drug abusers significant reductions in DA D2 receptors and in DA release. We postulate that this hypodopaminergic state would result in a decreased sensitivity to natural reinforcers perpetuating the use of the drug as a means to compensate for this deficit and contributing to the anhedonia and dysphoria seen during withdrawal. Because the D2 reductions are associated with decreased activity in the anterior cingulate gyrus and in the orbitofrontal cortex we postulate that this is one of the mechanisms by which DA disruption leads to compulsive drug administration and the lack of control over drug intake in the drug-addicted individual. This is supported by studies showing that during craving these frontal regions become hyperactive in proportion to the intensity of the craving. Craving is also associated with activation of memory circuits including the amygdala (implicated in conditioned learning), hippocampus (implicated in declarative learning), and dorsal striatum (implicated in habit learning) all of which receive DA innervation. We therefore postulate that dopamine contributes to addiction by disrupting the frontal cortical circuits that regulate motivation, drive, and self-control and by memory circuits that increase the motivational salience of the drug and drug-associated stimuli.     

Pubertal status associations with reward and threat sensitivities and subcortical brain volumes during adolescence

Adolescence is characterized by complex developmental processes that impact behavior, biology, and social functioning. Two such adolescence-specific processes are puberty and increases in reward sensitivity. Relations between these processes are poorly understood. The present study focused on examining unique effects of puberty, age, and sex on reward and threat sensitivities and volumes of subcortical brain structures relevant for reward/threat processing in a healthy sample of 9–18 year-olds. Unlike age, pubertal status had a significant unique positive relationship with reward sensitivity. In addition, there was a trend for adolescent females to exhibit higher threat sensitivity with more advanced pubertal development and higher reward and threat sensitivity with older age. Similarly, there were significant puberty by sex interaction effects on striatal volumes, i.e., left nucleus accumbens and right pallidum. The present pattern of results suggests that pubertal development, independent of chronological age, is uniquely associated with reward hypersensitivity and with structural differences in striatal regions implicated in reward processing.     

Where is the chocolate? Rapid spatial orienting toward stimuli associated with primary rewards

Some stimuli can orient attentional resources and access awareness even if they appear outside the focus of voluntary attention. Stimuli with low-level perceptual salience and stimuli with an emotional content can modulate attention independently of voluntary processes. In Experiment 1, we used a spatial cuing task to investigate whether stimuli that are controlled for their perceptual salience can modulate the rapid orienting of attention based exclusively on their affective relevance. Affective relevance was manipulated through a Pavlovian conditioning paradigm in which an arbitrary and affectively neutral perceptual stimulus was associated with a primary reward (i.e., a chocolate odor). Results revealed that, after conditioning, attentional resources were rapidly oriented toward the stimulus that was previously associated with the reward. In Experiment 2, we used the very same conditioning procedure, but we devaluated the reward after conditioning for half of the participants through a sensory-specific satiation procedure. Strikingly, when the reward was devaluated, attention was no longer oriented toward reward-associated stimuli. Our findings therefore suggest that reward associations rapidly modulate visual processing independently of both voluntary processing and the perceptual salience of the stimulus. This supports the notion that stimuli associated with primary rewards modulate rapid attention orienting on the basis of the affective relevance of the stimulus.     

Positive expectancies and perceived impaired control mediate the influence of reward drive and rash impulsiveness on alcohol use

Recent factor analytic studies indicate that the broad trait of impulsivity comprises at least two distinct dimensions with regard to substance use. Thus, a two-factor model of impulsivity, comprising reward drive (i.e., sensitivity to rewarding stimuli) and rash impulsiveness (i.e., rash behaviour devoid of forethought), has been proposed. It is argued that distinct cognitive processes may mediate the association of these impulsivity factors with alcohol use. Specifically, it was hypothesised that drinking expectancies would mediate the association between reward drive and alcohol use, and that perceived impaired control would mediate the effect of rash impulsiveness on alcohol. Utilising established scales, 132 participants aged 18 to 70 years were surveyed in order to assess the capacity of the two-factor model to differentially predict alcohol use through distinct cognitive mediators. The hypotheses were supported, providing support for a two-factor approach. Thus, reward drive and rash impulsiveness appear to influence alcohol use through distinct cognitive processes.