Department of Psychology, University of British Columbia, Vancouver, Canada.
Human Vision and Eye Movement Laboratory, Departments of Medicine (Neurology), Ophthalmology and Visual Science, University of British Columbia, Vancouver, Canada.
Parkinsonism Relat Disord. 2019 Sep;66:189-194. doi: 10.1016/j.parkreldis.2019.08.014. Epub 2019 Aug 26.
Clinical evidence suggests that Parkinson's Disease (PD) patients are risk averse. Dopaminergic therapy has been reported to increase risk tolerance, but the underlying mechanisms are unclear. Some studies have suggested an amplification of subjective reward value, consistent with the role of dopamine in reward value coding. Others have reported value-independent risk enhancement. We evaluated the value-dependence of the effects of PD and its therapy on risk using tasks designed to sensitively measure risk over a wide range of expected values.
36 patients with idiopathic PD receiving levodopa monotherapy and 36 healthy matched controls performed two behavioural economic tasks aimed at quantifying 1) risk tolerance/aversion in the gain frame and 2) valuation of potential gains relative to losses. PD patients performed the tasks on and off their usual dose of levodopa in randomized order; controls performed the same tasks twice.
Relative to the controls, unmedicated PD patients showed significant value-independent risk aversion in the gain frame, which was normalized by levodopa. PD patients did not differ from controls in their valuation of gains relative to losses. However, across both tasks and regardless of medication, choices of the patients were more determined by expected values of the prospects than those of controls.
Dopamine deficiency in PD was associated with risk aversion, and levodopa promoted riskier choice in a value-independent manner. PD patients also showed an increased sensitivity to expected value, which was independent of levodopa and does not appear to result directly from dopamine deficiency.
临床证据表明帕金森病（PD）患者是风险规避者。多巴胺能治疗已被报道能增加风险容忍度，但潜在的机制尚不清楚。一些研究表明，主观奖励价值的放大，与多巴胺在奖励价值编码中的作用一致。另一些研究报告了与价值无关的风险增强。我们使用旨在在广泛的预期价值范围内敏感地测量风险的任务，评估了 PD 及其治疗对风险的影响的价值依赖性。
36 名接受左旋多巴单药治疗的特发性 PD 患者和 36 名健康匹配的对照者进行了两项行为经济学任务，旨在定量测量 1）在收益框架中风险容忍/回避和 2）相对于损失的潜在收益的估值。PD 患者在随机顺序下接受常规剂量的左旋多巴治疗或不接受治疗，而对照组则两次完成相同的任务。
与对照组相比，未经治疗的 PD 患者在收益框架中表现出显著的与价值无关的风险回避，而左旋多巴使这种回避正常化。PD 患者在相对于损失的收益估值方面与对照组没有差异。然而，在两个任务中，无论是否接受治疗，患者的选择更多地取决于预期价值，而不是对照组。
PD 中的多巴胺缺乏与风险回避有关，而左旋多巴以与价值无关的方式促进了更冒险的选择。PD 患者还表现出对预期价值的敏感性增加，这与左旋多巴无关，似乎也不是直接由多巴胺缺乏引起的。
