物质成瘾及其戒除:基于反转学习的视角

Substance Addiction and Its Withdrawal: A Perspective of Reversal Learning

物质成瘾与反转学习损伤密切相关,成瘾者往往不能灵活地适应变化的刺激—结果的联结,这可能进一步加剧成瘾者的物质使用。近年来研究发现,物质成瘾者的反转学习相关的腹外侧前额和背外侧前额等脑区激活异常,这些异常与成瘾者的冲动性和强迫性有关。此外,个体的反转学习能力对其成瘾行为具有一定预测性。今后应增加对不同类型物质成瘾者的反转学习脑机制及物质相关线索对成瘾者反转学习影响的研究,并且进一步探讨成瘾者的冲动性和强迫性对其反转学习的调节及个体反转学习能力对其成瘾行为的预测。

Substance addiction has been a worldwide problem characterized by the lack of control over the use of substances in spite of increasingly negative consequences. It not only damages the addicts＇ physical and mental health, but also threatens the social stability. There is evidence that reversal learning plays an important role in the occurrence and development of addiction. Reversal learning is the ability to update the stimulus- outcome associations according to the changing environment. It has to do with people＇s social and emotional behavior. In a classical reversal learning task, subjects are presented with two visual stimuli simultaneously. One is accompanied by a reward and the other accompanied by a punishment. Subjects are required to choose the stimulus that could bring the reward to them through trial-error learning. After a period of time, the stimulus previously associated with reward will lead to punishment, whereas the stimulus previously associated with punishment will lead to reward. Then the subjects need to establish the new stimulus-outcome associations. However, the research on reversal learning in substance addiction has showed that addicts usually have problem with adapting their choice to reward contingencies. Once they learned that a specific stimulus has a certain outcome, they may struggle to learn that the same stimulus is later associated with a different outcome. Specifically, substance users may continue to attribute positive outcomes to some stimuli even in conditions when it has changed. These findings have also been confirmed by studies on laboratory animals. The present paper reviews the research on addicts＇ reversal learning： First of all, although a few studies reported that there was no reversal learning deficits in certain substance addicts （e.g., heroin users）, most studies showed impaired reversal learning among substance addicts. In addition, there are two forms of reversal learning deficits： perserveration and excessive switching, respectively reflecting impulsivity and compulsivity. In the next place, anomalous activities in reversal-specific brain areas, such as the ventrolateral prefrontal cortex （VLPFC） and the dorsolateral prefrontal cortex （DLPFC）, have been found among the substance addicts compared with the controls. Such results provided evidence for understanding behavioral impairment from a physiological perspective. What＇s more, the findings of reversal learning in the context of substance-related stimuli are mixed, which may derive from different types of reversal learning tasks. In the end, the reversal learning ability could predict addictive behavior. Individuals with poor reversal learning are more likely to use addictive substances. However, there are still some unclear issues needed to be further explored in the future： （1） The brain mechanism of reversal learning deficits in different types of substance addicts; （2） The influences of substance-related stimuli on addicts＇ reversal learning; （3） The effects of the addicts＇ impulsivity and compulsivity on their reversal learning; （4）The predictive power of reversal learning on addictive behavior. All in all, understanding the key role of reversal learning in substance addiction is not only rather meaningful for understanding the mechanism of addiction, but also can provide a new direction for treatment and prevention of substance addiction.