Schott Björn H, Niehaus Ludwig, Wittmann Bianca C, Schütze Hartmut, Seidenbecher Constanze I, Heinze Hans-Jochen, Düzel Emrah
Leibniz-Institute for Neurobiology, Brenneckestr. 6, Magdeburg 39118 , Germany.
Brain. 2007 Sep;130(Pt 9):2412-24. doi: 10.1093/brain/awm147. Epub 2007 Jul 11.
The ability to learn stimulus-reward associations on the basis of reward prediction errors critically depends on the mesolimbic dopaminergic system including the dopaminergic midbrain and the ventral striatum. It is known that healthy elderly and patients with Parkinson's disease are less proficient than healthy young adults in learning stimulus-reward contingencies, but it is unclear whether this is due to dysfunctional mesolimbic reward prediction or due to deficiency in processing the rewards per se. We used a well-established event-related fMRI reward-prediction paradigm to address this question. Young adults showed the well-replicated pattern of midbrain and ventral striatal activation for stimuli that predicted monetary reward when compared with stimuli that predicted neutral feedback. Also, as expected, the predicted reward feedback itself did not elicit a mesolimbic response. Healthy elderly subjects and unmedicated early-stage idiopathic Parkinson's disease patients showed the opposite pattern with an absent mesolimbic reward prediction response, but mesolimbic activation to the reward feedback itself. This suggests that the healthy elderly and Parkinson's disease patients were less proficient in learning the predictive value of the reward cues despite preserved mesolimbic processing of reward prediction errors. Parkinson's disease patients additionally displayed a relatively increased response of the anterior cingulate during reward feedback processing and diminished functional connectivity of the midbrain and ventral striatum. Our results are compatible with existing behavioural evidence that both groups exhibit a particularly pronounced deficit in learning from positive feedback and support the view that a tendency to underestimate expected values of reward cues might underlie this deficit. Furthermore, alterations in reward processing in Parkinson's disease extend beyond accelerated ageing effects and include altered connectivity within the mesolimbic system.
基于奖励预测误差学习刺激 - 奖励关联的能力严重依赖于中脑边缘多巴胺能系统，包括多巴胺能中脑和腹侧纹状体。已知健康老年人和帕金森病患者在学习刺激 - 奖励偶联方面不如健康年轻人熟练，但尚不清楚这是由于中脑边缘奖励预测功能失调，还是由于处理奖励本身存在缺陷。我们使用一种成熟的事件相关功能磁共振成像奖励预测范式来解决这个问题。与预测中性反馈的刺激相比，年轻人在预测金钱奖励的刺激下，中脑和腹侧纹状体激活呈现出反复出现的模式。同样，正如预期的那样，预测的奖励反馈本身并未引发中脑边缘反应。健康老年人和未用药的早期特发性帕金森病患者表现出相反的模式，即中脑边缘奖励预测反应缺失，但对奖励反馈本身有中脑边缘激活。这表明，尽管中脑边缘对奖励预测误差的处理得以保留，但健康老年人和帕金森病患者在学习奖励线索的预测价值方面不太熟练。帕金森病患者在奖励反馈处理过程中前扣带回的反应也相对增加，且中脑和腹侧纹状体的功能连接减弱。我们的结果与现有行为证据一致，即两组在从积极反馈中学习方面都表现出特别明显的缺陷，并支持这样一种观点，即低估奖励线索预期值的倾向可能是这种缺陷的基础。此外，帕金森病中奖励处理的改变超出了加速衰老的影响，还包括中脑边缘系统内连接的改变。
