Hill Daniel F, Hickman Robert W, Al-Mohammad Alaa, Stasiak Arkadiusz, Schultz Wolfram
Department of Physiology, Development and Neuroscience , University of Cambridge, Cambridge CB2 3DY, United Kingdom.
bioRxiv. 2024 May 10:2023.01.20.524896. doi: 10.1101/2023.01.20.524896.
The dopamine reward prediction error signal is known to be subjective but has so far only been assessed in aggregate choices. However, personal choices fluctuate across trials and thus reflect the instantaneous subjective reward value. In the well-established Becker-DeGroot-Marschak (BDM) auction-like mechanism, participants are encouraged to place bids that accurately reveal their instantaneous subjective reward value; inaccurate bidding results in suboptimal reward ('incentive compatibility'). In our experiment, male rhesus monkeys became experienced over several years to place accurate BDM bids for juice rewards without specific external constraints. Their bids for physically identical rewards varied trial by trial and increased overall for larger rewards. In these highly experienced animals, responses of midbrain dopamine neurons followed the trial-by-trial variations of bids despite constant, explicitly predicted reward amounts. Inversely, dopamine responses were similar with similar bids for different physical reward amounts. Support Vector Regression demonstrated accurate prediction of the animals' bids by as few as twenty dopamine neurons. Thus, the phasic dopamine reward signal reflects instantaneous subjective reward value.
多巴胺奖励预测误差信号已知是主观的，但迄今为止仅在总体选择中进行了评估。然而，个人选择在不同试验中会有所波动，因此反映了即时主观奖励价值。在成熟的贝克尔 - 德格鲁特 - 马尔沙克（BDM）类拍卖机制中，鼓励参与者出价，以准确揭示其即时主观奖励价值；出价不准确会导致奖励次优（“激励相容性”）。在我们的实验中，雄性恒河猴经过数年的训练，在没有特定外部约束的情况下，能够准确地对果汁奖励进行BDM出价。它们对物理上相同的奖励的出价在每次试验中都有所不同，并且对于更大的奖励总体上会增加。在这些经验丰富的动物中，尽管奖励量恒定且明确可预测，但中脑多巴胺神经元的反应仍跟随出价的逐次试验变化。相反，对于不同物理奖励量的相似出价，多巴胺反应相似。支持向量回归表明，仅用二十个多巴胺神经元就能准确预测动物的出价。因此，阶段性多巴胺奖励信号反映了即时主观奖励价值。
