Willner P, Benton D, Brown E, Cheeta S, Davies G, Morgan J, Morgan M
Centre for Substance Abuse Research, Department of Psychology, University of Wales, Swansea, UK.
Psychopharmacology (Berl). 1998 Apr;136(3):272-83. doi: 10.1007/s002130050566.
This study consisted of two experiments, one in rats and one in human volunteers, that used the identical progressive ratio (PR) operant procedure. In both experiments, responding was reinforced under a progressively increasing work requirement, and different groups of subjects received reinforcers that varied in sweetness. In experiment 1, rats were subjected to chronic mild stress, a well-validated animal model of depression. Performance under the PR schedule increased in subjects reinforced with conventional precision pellets (which contain 10% sucrose) or very sweet pellets, but not in subjects reinforced with sugar-free pellets. In experiment 2, volunteers were subjected to a depressive musical mood induction. Performance under the PR schedule increased in subjects reinforced with chocolate buttons, but not in subjects reinforced with with buttons made from the relatively unpalatable chocolate substitute carob. In experiment 2, depressive mood induction also increased chocolate craving, as measured by a novel questionnaire, and there were significant correlations between chocolate craving and chocolate-reinforced PR performance. These results suggest that performance under the PR schedule provides a measure of craving rather than reward, and that craving for sweet rewards is increased by depressive mood induction in both animal and human models. Implications for the interpretation of pharmacological studies using the PR procedure are also discussed.
本研究包括两项实验，一项以大鼠为对象，另一项以人类志愿者为对象，均采用相同的渐进比率（PR）操作性程序。在两项实验中，反应在逐渐增加的工作要求下得到强化，不同组别的受试者接受甜度不同的强化物。在实验1中，大鼠遭受慢性轻度应激，这是一种经过充分验证的抑郁症动物模型。在PR程序下，用传统精确颗粒（含10%蔗糖）或非常甜的颗粒强化的受试者表现有所提高，但用无糖颗粒强化的受试者则没有。在实验2中，志愿者接受抑郁情绪音乐诱导。在PR程序下，用巧克力纽扣强化的受试者表现有所提高，但用相对难吃的巧克力替代品角豆制成的纽扣强化的受试者则没有。在实验2中，通过一份新颖的问卷测量发现，抑郁情绪诱导也增加了对巧克力的渴望，并且对巧克力的渴望与巧克力强化的PR表现之间存在显著相关性。这些结果表明，PR程序下的表现提供了一种对渴望而非奖励的衡量，并且在动物和人类模型中，抑郁情绪诱导都会增加对甜味奖励的渴望。还讨论了对使用PR程序的药理学研究解释的影响。
