Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3DY, United Kingdom.
J Neurosci. 2010 Jan 13;30(2):534-44. doi: 10.1523/JNEUROSCI.4009-09.2010.
Animals depend on a large variety of rewards but their brains have a limited dynamic coding range. When rewards are uncertain, neuronal coding needs to cover a wide range of possible rewards. However, when reward is likely to occur within a specific range, focusing the sensitivity on the predicted range would optimize the discrimination of small reward differences. One way to overcome the trade-off between wide coverage and optimal discrimination is to adapt reward sensitivity dynamically to the available rewards. We investigated how changes in reward distribution influenced the coding of reward in the orbitofrontal cortex. Animals performed an oculomotor task in which a fixation cue predicted the SD of the probability distribution of juice volumes, while the expected mean volume was kept constant. A subsequent cue specified the exact juice volume obtained for a correct saccade response. Population responses of orbitofrontal neurons that reflected the predicted juice volume showed adaptation to the reward distribution. Statistical tests on individual responses revealed that a quarter of value-coding neurons shifted the reward sensitivity slope significantly between two reward distributions, whereas the remaining neurons showed insignificant change or lack of adaptation. Adaptations became more prominent when reward distributions changed less frequently, indicating time constraints for assessing reward distributions and adjusting neuronal sensitivity. The observed neuronal adaptation would optimize discrimination and contribute to the efficient coding of a large variety of potential rewards by neurons with limited dynamic range.
动物依赖于多种奖励，但它们的大脑动态编码范围有限。当奖励不确定时，神经元编码需要覆盖可能奖励的广泛范围。然而，当奖励很可能在特定范围内发生时，将敏感性集中在预测范围内将优化对小奖励差异的辨别。克服广泛覆盖和最佳辨别之间的权衡的一种方法是动态地使奖励敏感性适应可用的奖励。我们研究了奖励分布的变化如何影响眶额皮层中的奖励编码。动物执行眼球运动任务，其中固定线索预测果汁量概率分布的 SD，而预期平均量保持不变。随后的线索指定了正确扫视反应获得的确切果汁量。反映预测果汁量的眶额皮层神经元的群体反应表现出对奖励分布的适应。对单个反应的统计检验表明，四分之一的价值编码神经元在两种奖励分布之间显著改变了奖励敏感性斜率，而其余神经元则没有明显变化或缺乏适应。当奖励分布变化不频繁时，适应变得更加明显，这表明评估奖励分布和调整神经元敏感性存在时间限制。观察到的神经元适应将优化辨别，并有助于神经元在有限的动态范围内对多种潜在奖励进行有效编码。
