Flagel Shelly B, Akil Huda, Robinson Terry E
Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, USA.
Neuropharmacology. 2009;56 Suppl 1(Suppl 1):139-48. doi: 10.1016/j.neuropharm.2008.06.027. Epub 2008 Jun 21.
Drugs of abuse acquire different degrees of control over thoughts and actions based not only on the effects of drugs themselves, but also on predispositions of the individual. Those individuals who become addicted are unable to shift their thoughts and actions away from drugs and drug-associated stimuli. Thus in addicts, exposure to places or things (cues) that has been previously associated with drug-taking often instigates renewed drug-taking. We and others have postulated that drug-associated cues acquire the ability to maintain and instigate drug-taking behavior in part because they acquire incentive motivational properties through Pavlovian (stimulus-stimulus) learning. In the case of compulsive behavioral disorders, including addiction, such cues may be attributed with pathological incentive value ("incentive salience"). For this reason, we have recently begun to explore individual differences in the tendency to attribute incentive salience to cues that predict rewards. When discrete cues are associated with the non-contingent delivery of food or drug rewards some animals come to quickly approach and engage the cue even if it is located at a distance from where the reward will be delivered. In these animals the reward-predictive cue itself becomes attractive, eliciting approach towards it, presumably because it is attributed with incentive salience. Animals that develop this type of conditional response are called "sign-trackers". Other animals, "goal-trackers", do not approach the reward-predictive cue, but upon cue presentation they immediately go to the location where food will be delivered (the "goal"). For goal-trackers the reward-predictive cue is not attractive, presumably because it is not attributed with incentive salience. We review here preliminary data suggesting that these individual differences in the tendency to attribute incentive salience to cues predictive of reward may confer vulnerability or resistance to compulsive behavioral disorders, including addiction. It will be important, therefore, to study how environmental, neurobiological and genetic interactions determine the extent to which individuals attribute incentive value to reward-predictive stimuli.
滥用药物对思想和行为的控制程度各不相同，这不仅取决于药物本身的作用，还取决于个体的易感性。那些成瘾的个体无法将他们的思想和行为从药物及与药物相关的刺激中转移出来。因此，对于成瘾者来说，接触以前与吸毒相关的场所或事物（线索）往往会引发再次吸毒行为。我们和其他人推测，与药物相关的线索获得维持和引发吸毒行为的能力，部分原因是它们通过巴甫洛夫式（刺激-刺激）学习获得了激励动机特性。在包括成瘾在内的强迫行为障碍中，此类线索可能被赋予了病理性激励价值（“激励显著性”）。出于这个原因，我们最近开始探索个体在将激励显著性赋予预测奖励的线索的倾向上的差异。当离散线索与食物或药物奖励的非偶然发放相关联时，一些动物即使线索位于离奖励发放地点有一段距离的地方，也会很快接近并与线索互动。在这些动物中，奖励预测线索本身变得具有吸引力，引发对它的接近，大概是因为它被赋予了激励显著性。形成这种条件反应类型的动物被称为“信号追踪者”。其他动物，即“目标追踪者”，不会接近奖励预测线索，但在线索出现时，它们会立即前往食物将被发放的地点（“目标”）。对于目标追踪者来说，奖励预测线索没有吸引力，大概是因为它没有被赋予激励显著性。我们在此回顾初步数据，这些数据表明，在将激励显著性赋予预测奖励的线索的倾向上的这些个体差异，可能导致对包括成瘾在内的强迫行为障碍的易感性或抵抗力。因此，研究环境、神经生物学和基因相互作用如何决定个体将激励价值赋予奖励预测刺激的程度将很重要。
